Impulse buying: A systematic literature review and future research directions

This paper performs a comprehensive analysis of academic research on impulse buying following a systematic literature review approach. Drawing on the TCCM framework suggested by Paul and Rosado-Serrano, we synthesize the impulse buying literature and develop a future research agenda. Accordingly, this review synthesizes impulse buying research in terms of theory development, context, characteristics, and methodologies to examine the development of the literature over time. This systematic review shows that impulse buying research is fragmented and still developing due to its transition from a traditional retail environment into different online channels. Furthermore, this paper proposes a conceptual framework based on the literature synthesis, presenting antecedents and mediators of impulse buying behaviour. Finally, this review identifies overlooked areas in impulse buying literature and provides insightful directions to advance research in the domain. Overall, this research effort makes a significant contribution to consumer behaviour literature, specifically to impulse buying literature.


| INTRODUCTION
Innovations, such as self-service kiosks, product exchange offers, credit cards and monthly instalment schemes, have significantly simplified shopping for consumers (Dekimpe et al., 2020;Sheth, 2021).
Consequently, impulsive, recreational and frivolous purchasing has become enjoyable and effortless. Hence, impulse buying has emerged as a topic of great interest to academics and practitioners.
Researchers define impulse buying as an unplanned and unintended purchase made rapidly, on the spot, without much reflection, preceded by exposure to a stimulus and a sudden and powerful buying urge (Beatty & Ferrell, 1998;Zheng et al., 2019). While utilitarian considerations largely shape planned and habitual purchasing, high-arousal emotions and hedonic motives characterize impulse buying .
Marketers and retailers traditionally utilize external stimuli, such as in-store promotions and advertising, to trigger impulse shopping Yi & Jai, 2020). From consumers' perspective, a moderate level of impulse buying is considered a socially acceptable recreational activity and is relatively harmless. However, excessive levels of this behaviour can be detrimental to shoppers and lead to financial and psychological hardships .
Today impulse buying accounts for a large proportion of sales within the modern retail industry Zhang et al., 2020). In the United States alone, impulse purchases generate $17.78 billion in annual profit for retailers, with consumers spending on average $5400 per year on unplanned purchases (Tran, 2019). The COVID-19 crisis has led to a surge in impulse shopping. Recent polls indicate that American consumers' average monthly spending on impulse purchases has increased by 18% since the beginning of the pandemic (Keenan, 2021;Li Cain, 2020). Despite the detrimental effect of COVID-19 on the global economy, experts attribute 20% of spending in the retail sector's sales to impulse purchases (Repko, 2020).
The above statistics suggest the increasing importance of impulse buying in the global retail industry. Hence, the impulse buying phenomenon has attracted interest from researchers, who have taken diverse perspectives on the subject and employed different conceptualizations and methods. Although many studies have been conducted on impulse buying, the literature on the topic is still highly fragmented (Kimiagari & Malafe, 2021;Li et al., 2021). In particular, impulse buying has been investigated by academics from different research disciplines, including marketing , information systems , business and management (Ahmed et al., 2020) and tourism ). Yet, the research findings are inconsistent and divided, preventing a complete understanding of factors affecting impulse buying behaviour.
Moreover, impulse buying researchers have employed a diverse range of underpinning theories, indicating that theoretical perspectives in the domain are fragmented and still emerging. Therefore, a synthesis of theories and models used in impulse buying research will benefit the literature and aid its progress. Finally, global technological and marketing innovations and trends resulted in the transition of impulse buying from a traditional in-store retail environment into different online channels-electronic commerce, social commerce, and mobile commerce. Consequently, the literature investigating impulse buying on these online platforms needs to be synthesized to determine the future research trajectory.
The fragmented state of impulse buying literature can be remedied by a comprehensive discussion of research in this domain and an analysis of its current dynamics. The research will benefit from a synthesis of factors affecting impulse buying, theoretical perspectives adopted in the literature, and sub-domains investigating impulse buying on different online platforms. Thus, a state-of-the-art synthesis of impulse buying research is essential to assess the development of the literature and identify avenues for future research in the domain. Paul and Criado (2020) suggest conducting a structured systematic literature review to consolidate expanding and dispersed knowledge in a domain. Structured review synthesizes the literature in terms of theories, contexts, characteristics, and methods, providing concrete future research suggestions to advance a field of research (Paul & Criado, 2020). Therefore, the structured review approach is appropriate for summarizing and systematically evaluating the research in the impulse buying domain (Chan et al., 2017).
A few literature reviews have been written on impulse buying over the years. The two systematic reviews published in the domain (i.e., Mandolfo & Lamberti, 2021;Xiao & Nicholson, 2013) have a narrow scope and do not synthesize the impulse buying research in terms of years of publication, commonly used theories, and constructs. For instance, the most recent systematic review written by Mandolfo and Lamberti (2021) examined only research methods used in the impulse buying domain. Hence, the existing systematic reviews do not provide an up-to-date, state-of-the-art synthesis of the impulse buying literature. Thus, a lack of an up-to-date systematic literature review on impulse buying warrants a need to systematically review the literature to provide a state-of-the-art synthesis of impulse buying research.
Therefore, this research aims to systematically review the impulse buying literature and identify gaps, opportunities, and future research directions in this domain. This comprehensive analysis consolidates impulse buying research from a marketing perspective and includes its newest branches, for example, mobile commerce and social commerce. This review has the following three research objectives. The The remainder of this review is structured as follows. The next section describes the methodology employed by this research effort.
It is followed by the findings and discussion section, which presents the synthesis of impulse buying literature. Next, future research directions are provided, followed by theoretical and practical implications and a conclusion.  (Paul & Criado, 2020). Our review synthesizes the impulse buying literature, identifies research gaps, and proposes future research directions following the systematic literature review approach. Paul and Criado (2020) recognize three categories of systematic reviews: domain-based, theory-based, and method-based. This review follows the domain-based approach, synthesizing and extending a body of literature in one domain or topic area (Palmatier et al., 2018).
A structured systematic literature review technique is a reliable tool for synthesizing research, as it rigorously follows pre-set guidelines and scientific methods which are reproducible and explicit (Gopalakrishnan & Ganeshkumar, 2013;Paul & Criado, 2020

| Topic selection
We adopt the structured systematic review method to review the extant literature on impulse buying. Topic selection is a crucial step in writing an impactful literature review (Paul & Criado, 2020). Paul and Criado (2020) advise that a systematic review on a selected topic should not have been recently published unless it proposes new contributions or research agenda. Accordingly, a search via Google Scholar identified 14 literature reviews in the impulse buying domain (see Table 1).
For instance, the most recent narrative review by Mathur (2019) examined impulse buying definition and antecedents based on just 19 impulse buying studies. Further, four out of the 14 review papers adopted a meta-analysis approach (i.e., Amos et al., 2014;Iyer et al., 2020;Paul et al., 2022;Zhao et al., 2021). For example , Paul et al. (2022) conducted a meta-analysis of 33 empirical papers to identify common antecedents of consumers' buying urge. However, a meta-analysis is a different method from a structured systematic review. While both systematic review and meta-analysis examine a volume of previous research, the former synthesizes previous findings while the latter makes a statistical assessment of extant quantitative studies (Pati & Lorusso, 2018;Paul & Criado, 2020;Piper, 2013 Xiao & Nicholson, 2013). However, two out of the four systematic reviews (i.e., Abdelsalam et al., 2020;Chan et al., 2017) do not assess the entire volume of impulse buying literature but are limited to electronic commerce and social commerce contexts. Accordingly, two systematic reviews have a main focus on impulse buying (i.e., Mandolfo & Lamberti, 2021;Xiao & Nicholson, 2013). However, these papers are limited in scope. For instance, Xiao and Nicholson (2013) systematically reviewed the literature to identify impulse buying antecedents and consequences. Their study examined 183 peerreviewed journal articles published between 1940 and 2011 and is therefore outdated. A significant number of studies have been published since 2011, and impulse buying research has progressed much since then.
Thus, it does not provide an up-to-date, state-of-the-art synthesis of impulse buying literature.
The systematic review by Mandolfo and Lamberti (2021) investigated only research methods used in impulse buying literature by examining 54 journal articles published between 1982 and 2020. Although Mandolfo and Lamberti (2021) conducted their review recently, they have not provided a state-of-the-art synthesis of impulse buying literature. In particular, their review synthesizes only methods used in the literature. However, a structured systematic review also needs to synthesize theories, constructs, and contexts used in the domain (Paul & Rosado-Serrano, 2019). Thus, the extant structured reviews on impulse buying have a limited scope and do not examine the development of the impulse buying domain over the years, commonly used theories, and constructs. Accordingly, an up-to-date structured systematic review on impulse buying does not exist, resulting in an ambiguous state of research. Hence, a structured systematic review is needed to synthesize the literature on impulse buying.

| Search strategy
After choosing a topic, databases and keywords for the article search have to be selected. The following sections explain how we chose them.

| Keywords selection
This review followed the strategy suggested by Talwar et al. (2020) for identifying keywords for article search. Accordingly, as a first step, a search was performed via the Google Scholar platform using "impulse buying" as a search word. Next, the papers within the first 100 results were downloaded and screened. Their titles, abstracts and keywords were assessed to generate a new list of keywords for this review's literature search.
Based on the screening results, it was found that the most frequently used keywords in the papers' titles, abstracts and keyword lists are 'impulse buying', 'impulse purchasing', 'impulse shopping', 'impulsive buying', 'impulse purchase' and 'urge to buy impulsively'.
Thus, these keywords were collected and used to search for relevant papers across all the databases 1 . Hence, any papers with these keywords identified in the title, abstract or keyword list were included in this review with due consideration paid to the inclusion and exclusion criteria explained in the next section.

| Journal selection and inclusion/exclusion criteria
To select relevant academic articles for this review, inclusion and exclusion criteria were outlined consistent with past research (Nanda & Banerjee, 2021;Paul & Rosado-Serrano, 2019). Accordingly, an article eligible for this review should (1) be a scholarly work, (2) be written in English, (3) be published in a peer-reviewed journal and (4) have a focus on impulse buying. Additionally, to ensure the quality of the journals, consistent with previous systematic review papers (Goyal & Kumar, 2021), the Australian Business Dean Council (ABDC) journal quality list and impact factor in Journal Citation Reports (JCR) were used as proxies. Accordingly, papers were considered for this review only if published in journals listed as A or A* The authors did not provide information on the number of studies examined in their review. The number of papers is based on relevant references provided in the authors' reference list. b The year range was identified based on the earliest and latest reference used in the literature review process.
in ABDC or journals with an impact factor of one or above in JCR.
Only papers published in these journals were considered highquality research outputs.
The initial search of selected databases using specified keywords yielded a total of 1971 papers. The first step was to remove duplicate papers. Here, duplicate papers were the extra copies of papers downloaded multiple times from the same or different databases. Accordingly, 535 duplicate papers were excluded from further screening.
Then, inclusion and exclusion criteria were employed for the remaining 1436 papers. The first criterion was to remove non-scholarly work.
Non-scholarly work is publications in non-academic sources (e.g., newspapers, blogs, and trade journals). Therefore, 64 papers from non-scholarly sources were removed.

| FINDINGS AND DISCUSSIONS
The details of the 183 selected articles (i.e., author [s] with the year of publication, title and journal of publication) are presented in Table A1 (Appendix). All the papers were reviewed to examine the development of impulse buying research over time (this review's first objective) and propose a comprehensive conceptual framework (this review's second objective). The synthesis of impulse buying research is discussed in the following sections.

| Development of impulse buying research over the years
The initial step of the systematic literature review process involves breaking down the articles in terms of their year of publication. Such period-based distribution of papers in a domain allows us to examine the growth of a research topic over time. Additionally, it helps identify and track developments in the literature. The first academic paper on impulse buying was published in 1950 . Accordingly, this was considered the starting year for the systematic literature review. Hence, this review includes research papers published between 1950 and 2021. Figure  free-market economic model adopted by many countries worldwide, which drastically increased the rate and frequency of impulse buying (Vohs & Faber, 2007

| Journals of publication
As the next step of this synthesis, journals that published impulse buying papers were examined.

| Authorship
Next, the most cited contemporary impulse buying research was examined. Accordingly, Table 3

| Research setting
Next, this systematic review synthesizes the countries where the academic studies were carried out. Only empirical papers were Year-wise growth of impulse buying research considered for this research setting analysis where the data (i.e., sample) were drawn from a country. Eleven empirical studies were conducted in multiple countries, usually to examine cultural differences (Cakanlar & Nguyen, 2019;    The current review also synthesizes the data collection techniques used in impulse buying research. In terms of data collection methods, Table 5

| Theoretical perspectives
This review also synthesized the theories and models used in impulse buying research. have also been used in multiple studies. Table 6 demonstrates the diverse range of theoretical perspectives used in impulse buying research which possibly indicates that theoretical perspectives for impulse buying research are still emerging and progressing. A brief articulation of the repeatedly used theoretical perspectives follows.

| Stimulus-Organism-Response framework
Proposed by Mehrabian and Russell (1974) and extended by Jacoby  3.5.4 | Regulatory focus theory Higgins (1997) proposed regulatory focus theory (RFT) as a new goalpursuit theory, positing that people engage in approach or avoidance behaviour based on their self-regulatory orientation: either promotionfocused or prevention-focused. Promotion-focused individuals are driven by positive outcomes, seeking achievement and growth, while prevention-focused individuals look for security and focus on avoiding adverse outcomes (Higgins, 1997;Verplanken & Sato, 2011). Drawing on the RFT, Lin et al. (2018) found that promotion focus induces impulse buying and leads to post-purchase satisfaction, while prevention focus hinders impulse buying behaviour.

| Construal level theory
Research shows that the psychological distance between a consumer and a product determines impulse buying behaviour ( to an abstract perception (high-level construal) of that object. Conversely, the proximal psychological distance between an object and an individual leads to a more concrete perception (low-level construal) of that object (Liberman et al., 2007). Drawing on the CLT, Vonkeman et al. (2017) found that website cues can simulate a real shopping situation through their interactivity and vividness, decreasing the construal level, triggering an affective state in a consumer, and resulting in an impulsive urge.

| Latent state-trait theory
The latent state-trait (LST) theory articulates that human behaviour is determined by environmental characteristics (states), individual factors (traits) and interaction between these variables (Steyer et al., 1999). LST has been utilized in impulse buying research, including electronic commerce  and social commerce  contexts. Drawing on the LST, Wells et al. (2011) have shown that website quality (i.e., environmental characteristic) with the moderating effect of consumer impulsiveness (i.e., individual trait) trigger impulse buying. Similarly,  uncovered that the interaction between information quality of advertising and the number

| Flow theory
Flow theory posits that an individual engaged in an activity can enter a flow state, making the person experience positive emotions of great enjoyment and reduced self-consciousness (Csikszentmihalyi & Csikzentmihaly, 1990;Jackson & Marsh, 1996). Koufaris (2002) applied flow theory to online consumer behaviour and suggested shopping enjoyment as a major construct facilitating the buying process. Drawing on the flow theory,  reported that when consumers enjoy browsing a shopping website, they can experience positive emotions and time distortion, leading to increased exposure to marketing stimuli and impulse buying.

| Frequently used variables
The second objective of this systematic review is to develop a conceptual model depicting the antecedents and mediators of impulse buying behaviour. Accordingly, Table 7 presents the synthesis of the  Research links impulse buying proclivity to several consumer traits. The key consumer characteristics are personality traits.
Self-control is another consumer-related factor affecting impulse buying. A common cause of impulsive purchasing is a consumer's inability to resist buying temptation or exercise self-control (Baumeister, 2002). Self-control allows individuals to resist impulses and focus on long-term goals (De Ridder & Gillebaart, 2017). Consumers who possess low self-control are more likely to buy on impulse when shopping Xu et al., 2020).
Consumer resources are significant predictors of impulse buying (Atulkar & Kesari, 2018;Krishna et al., 2021). A shopping trip budget determines a consumer's buying power, and a larger budget can trigger positive emotions resulting in impulse buying (Badgaiyan & Verma, 2015;. Thus, consumers with extra money to spend are more likely to experience positive affect and make impulsive purchases (Beatty & Ferrell, 1998;.

Sociodemographic factors
Demographic variables are also prominent impulse buying predictors Normative and interpersonal influences strongly affect impulse buying behaviour Peck & Childers, 2006). Normative influence refers to social norms which set behavioural expectations for an individual to follow (Rook & Fisher, 1995).
peers, or a companion of the opposite gender in a shopping group, and friendly store staff, positively influence impulse buying (Badgaiyan & Verma, 2015;Cheng et al., 2013).

Marketing mix
Product-related factors (i.e., product type, features, packaging, and price) are among the major predictors of impulse buying behaviour . Products can either be hedonic and offer an enjoyable experience or utilitarian, providing functional benefits (Chen & Wang, 2016;Okada, 2005). Hedonic products are more likely to be bought on impulse (Chen & Wang, 2016;Kacen et al., 2012).
Retailers can also attract consumer attention and instigate impulse buying behaviour by running sales promotion activities Miao et al., 2019). Sales promotions provide utilitarian (money-saving) or hedonic (entertainment) benefits to consumers, with the combination of the two having the strongest effect on impulse buying . Promotions that provide immediate rewards to shoppers are especially effective in inciting impulse buying (Liao et al., 2009;Luo et al., 2021). For instance, price discounts and reductions speed up consumer decision-making and prompt impulse purchases (Chen & Wang, 2016). Research also shows that free shipping (Dawson & Kim, 2010), cash refund promotions (Chen & Wang, 2016), bundle offers  and added donations (Jeffrey & Hodge, 2007) can effectively stimulate impulse buying behaviour.
Store atmosphere prompts impulse buying by generating positive emotions of pleasure, shopping enjoyment and hedonic motives in consumers Nghia et al., 2021). The store layout, lighting, cleanliness, crowding and employee assistance create an appropriate atmosphere for impulse shopping (Badgaiyan & Verma, 2015;Mohan et al., 2013).
In an online context, e-store elements and their design facilitate impulse buying. Research shows that the quality of a website influences impulse purchasing (Akram, Hui, Kaleem Khan, et al., 2018;Kimiagari & Malafe, 2021). Specifically, shopping websites provide task-relevant and mood-relevant cues to consumers . Task-relevant cues of navigability, ease of use and information fit-to-task influence impulse buying (Kimiagari & Malafe, 2021;Xiang et al., 2016). Mood-relevant cues make the process of browsing enjoyable for consumers .
For instance, the visual appeal of a website and high-tempo music can trigger impulse purchases by stimulating shoppers' pleasure and arousal during browsing Zhang et al., 2020).

Online peer influence
Online reviews can trigger impulse buying urges during browsing Chen, Lu, et al., 2019). They also increase positive affect, enticing impulse buying if the review is of good quality, that is, highly useful to a consumer and originating from a credible source . In particular, online reviews with a strong hedonic message are more effective in triggering impulse buying than those that emphasize utilitarian information Zhang et al., 2018).
While browsing social commerce platforms, consumers are likely to encounter and interact with various social cues and engage in impulse buying as a result (Kimiagari & Malafe, 2021;Zafar et al., 2020). Posts and comments on social media make shoppers feel connected to an online community activating emotions of pleasure and arousal and leading to impulse buying Ju & Ahn, 2016;Zhao et al., 2019). Furthermore, digital celebrities' endorsements on social media can induce impulse buying among young adults during hedonic browsing Vazquez et al., 2020;.

Emotional response
Consumers' emotional responses play a key role in the impulse buying process Yi & Jai, 2020). For instance, emotions of pleasure, enjoyment and arousal mediate the effect of both store environment and promotional messages on impulse buying Zhang et al., 2021). Further, affect can mediate the relationship between consumer-related factors and impulse buying Liu et al., 2019). Additionally, impulse buying is often prompted by a flow experience activated by productrelated stimuli or the process of browsing Zhu et al., 2020). Overall, consumers' emotional responses mediate the T A B L E 6 (Continued)

Pre-purchase stage
Before making an impulse purchase, consumers experience an urge to buy impulsively Beatty & Ferrell, 1998).
Hence, researchers have used impulsive urge as a proxy measure of the actual impulse buying behaviour (e.g., Vonkeman et al., 2017;Yang et al., 2021). However, empirical research shows that impulsive urge does not guarantee a purchase but rather acts as a precursor and a mediating variable for the final impulse purchase Mohan et al., 2013;Yi & Jai, 2020).

| Designing an integrated conceptual framework
A conceptual framework has been developed integrating the most commonly used constructs in impulse buying research, that is, the antecedents and mediators of impulse buying behaviour. Figure 3 presents the framework.

| Domains in impulse buying research
In recent years, impulse buying has become a prominent research topic, following global technological and marketing innovations and trends. Impulse buying has been investigated in two broad domains of literature: traditional brick and mortar retailing and online retailing.
The latter dimension can be further divided into electronic commerce (e-commerce), social commerce (s-commerce) and mobile commerce (m-commerce), as illustrated in Figure 4 and Table 8. 3.8.1 | Traditional retailing-based impulse buying  conducted the first study in the traditional retailing domain and investigated the influence of impulse buying on holiday sales based on the type of store and product. However, early research has several conceptual and methodological shortcomings, that is, the definition and measurement of impulse buying were not well developed (Kollat & Willett, 1969;Rook, 1987;Weinberg & Gottwald, 1982). Hence, this research area remained stagnant and F I G U R E 3 Integrated conceptual framework largely ignored for decades. In the early 2000s, marketing and technological innovations increased the incidence of impulse buying leading to the re-emergence of interest in this research area. Hashmi et al.
(2020) conducted a recent study on impulse buying in the traditional retailing domain showing that store environment and hedonic shopping motives significantly influence shopping enjoyment and pleasure and stimulate impulse buying.

| Online retailing-based impulse buying
The emergence of the internet and digital technologies led to a new domain of impulse buying research: impulse buying in an online retail environment. Online impulse buying gained the attention of researchers due to its differences from traditional impulse buying (Jeffrey & Hodge, 2007). This research domain can be divided into three subdomains, that is, e-commerce, s-commerce and m-commerce.

E-commerce
Global e-commerce sales exceeded US$ 4.28 trillion in 2020 (Chevalier, 2021). Approximately 40% of purchases in this sector are impulsive (Stern, 2021). Furthermore, it is estimated that 80% of millennials regularly purchase impulsively from web stores (Johnson, 2018).

S-commerce
Retailers actively use social media platforms for their marketing activities.
For instance, 86.3% of businesses employ Facebook to conduct marketing activities (Guttman, 2020). Retailing on social networking sites is known as "social commerce" (s-commerce). S-commerce experiences rapid growth, with US sales in this sector increasing by 34.8% in 2021, F I G U R E 4 Domains in impulse buying research

M-commerce
The use of handheld devices for facilitating monetary transactions has increased immensely in the last decade, leading to the emergence of mobile commerce (m-commerce). In 2019, 65% of total retail website visits were by online shoppers who access the websites via smartphones, and 46% of those website visits proceeded to place an order (Coppola, 2021). M-commerce has made consumers more flexible in their shopping pursuits and generated more impulse buying opportunities (Chen & Yao, 2018). However, impulse buying research in the mcommerce context has been scarce, with just 13 studies identified by this review. The most recent article in this sub-domain has investigated the influence of consumers' perceived utilitarian and hedonic values on impulse buying on a mobile shopping platform .

General
Some online impulse buying studies are more general and not specific to a particular shopping context. Hence, this review places those articles in a separate sub-domain identified as 'general'. Kacen and Lee (2002) conducted a pioneer study in this area and investigated cultural and individual differences of impulse shoppers from a multi-country perspective. The latest research effort in this area investigated the role of shopping values and impulse buying tendencies in consumers' shopping wellbeing .

| FUTURE RESEARCH DIRECTIONS
Our review also proposes directions for future research in the impulse buying area that help accomplish the third research objective. Literature synthesis conducted in this review identified future research directions, which were then categorized using the TCCM framework adopted from Paul and Rosado-Serrano (2019). TCCM framework suggests organizing future research directions in four dimensions: Theories, Context, Characteristics and Methodologies. TCCM framework has been widely adopted for organizing future research directions in systematic literature review papers published in top-rated journals (Bhattacharjee et al., 2022;Billore & Anisimova, 2021).
Accordingly, the future research agenda for impulse buying research developed using the TCCM framework is discussed in detail below. A summary of future research directions is presented in Table 9.

| Theory development
The research. One such theoretical perspective is cue utilization theory. This theory posits that shoppers obtain extrinsic and intrinsic product information and evaluate it jointly to estimate product quality and make a purchase decision (Yan et al., 2019;Zhu et al., 2020). For instance, when the product is unfamiliar to consumers, they prioritize the most easily obtained cues (e.g., social cues) and rely on extrinsic cues provided by sellers (Kukar-Kinney & Xia, 2017;Yan et al., 2019;Zhu et al., 2020). Thus, T A B L E 9 Future research directions in impulse buying domain Theory development • Cue utilization theory can be applied to examine the interaction of extrinsic and intrinsic cues as antecedents of impulse buying. • Competitive arousal model can be employed to examine the mediating role of arousal in the impulse buying behaviour of consumers competing with other shoppers for time and quantity restricted deals.

Context
• Future researchers should examine impulse buying in various developed and developing countries for better generalizability of findings. • More studies need to investigate impulse buying in social commerce and mobile commerce contexts.

Characteristics
• Only a few specific sales promotion tactics employed in e-commerce have been tested in impulse buying research. Therefore, researchers need to examine whether prominent online sales tactics, such as flash sales and limited-edition products, stimulate impulse buying. • Future researchers need to examine how the absence of negative online reviews and average star ratings affect impulse buying. • Future research needs to examine whether specific negative emotional responses, for example, stress, anxiety and feeling of uncertainty, act as mediators in the impulse buying process. • More studies on the long-term consequences of impulse buying are needed. Future researchers can investigate the effect of hedonically rewarding online impulse purchases on the subjective wellbeing of consumers over time.

Methods
• Qualitative studies can explore novel factors that lead to impulse buying in the social commerce context.
• Mixed-method design is recommended for future impulse buying studies. A combination of qualitative and quantitative research should identify impulse buying antecedents in social commerce and validate the effects of these antecedents on impulse buying. the interaction of extrinsic and intrinsic cues as antecedents of impulse buying can be examined using the underpinnings of cue utilization theory.
The competitive arousal model is another promising theoretical approach that can be applied to impulse buying research. This theoretical perspective originates from a study investigating overspending in live auctions (Ku et al., 2005). According to the theory, perceived rivalry, social facilitation, time pressure and uniqueness of being first fuel auction participants' competitive arousal and impair their decision-making (Ku et al., 2005). Promotional messages emphasizing the scarcity of an offer may have a similar effect on consumers, leading to increased impulse buying . For example, when retailers highlight supply scarcity, they might trigger competitive arousal in shoppers and stimulate impulse purchases. The literature synthesis shows that arousal is among the prominent mediators of impulse buying Hashmi et al., 2020;Wu et al., 2021). Therefore, the application of competitive arousal theory could cast light on the role of emotional responses in impulse buying behaviour.

| Characteristics
The literature review shows that researchers primarily examined promotional and website stimuli, personality traits and cultural factors as antecedents of impulse buying. Hence, future research can examine whether specific sales promotional tactics used in e-commerce and online reviews can help trigger impulse buying. Researchers can also investigate the mediating role of negative emotional responses in the impulse buying process and the long-term consequences of impulse shopping on consumers' wellbeing. Characteristics-specific avenues for future research are described in more detail below.

| Impulse buying and online sales promotion tactics
Researchers have determined that sales promotions can stimulate impulse buying in a traditional retail environment Miao et al., 2019). However, only a few sales tactics employed in ecommerce have been tested in impulse buying research. In particular, Lo et al. (2016) found that several online sales techniques (i.e., buyone-get-one-free, group buying, limited time offers and limited quantities) influence impulse buying. Similarly,  examined the role of online bundle offers in driving impulse buying.
Nonetheless, some prominent sales tactics used in e-commerce have never been studied in the impulse buying domain. For example, the role of scarcity promotions used by online retailers has barely been covered. Examples of such scarcity promotional techniques that can be examined in the online impulse buying context include flash sales with countdown timers and limited-edition products. Tactics that incorporate time-limited free shipping (e.g., next-day delivery for purchase within a particular time frame) and guaranteed free returns also warrant investigation. Examining the above tactics and other online promotion techniques would provide practical guidance to marketers and e-retailers to trigger impulse purchases.

| Impulse buying and online social influence
With the emergence of social commerce, online social influence started shaping consumer behaviour and decision-making. Yet, consumers' online reviews posted on retailers' websites and social media platforms, as an online peer influence tool, have not been sufficiently examined in the impulse buying context. The literature briefly covered digital celebrities Zafar et al., 2020) and the number of likes , yet many other aspects of online social influence remain open for examination. For instance, the influence of the presence of negative and positive reviews and online ratings (e.g., average star rating) on impulse buying warrants investigation. Furthermore, hedonic and utilitarian values provided to shoppers by online reviews are likely to predict impulse buying. Additionally, the credibility (i.e., authenticity) of reviews potentially determined by the presence or absence of negative reviews might incite impulse purchases. Overall, online peer influence presents a promising area for future impulse buying research.

| Impulse buying and negative emotional responses
The outbreak of the COVID-19 pandemic has shown that consumers engage in panic buying and excessive stockpiling to cope with negative emotions of fear, stress, and anxiety Gupta et al., 2021;Naeem, 2021). Researchers also found that in times of crisis, uncertainty and isolation, consumers engage in herd behaviour, which leads to impulse purchases (Ahmed et al., 2020;Xiao et al., 2021). However, impulse buying research has primarily examined positive emotional responses, such as positive affect, enjoyment, and arousal, as mediators in the impulse buying process Wu et al., 2021;Zhang et al., 2020). Therefore, the question arises: do negative emotions also prompt impulse buying?
Specifically, future research needs to examine whether specific negative emotional responses, for example, stress, anxiety and feeling of uncertainty, act as mediators in the impulse buying process.

| Long-term consequences of impulse buying
Traditionally, a positive or negative view of impulse buying behaviour and its consequences for consumers depends on a researcher's academic discipline. For example, psychologists view impulse buying as harmful and believe it leads to compulsive shopping behaviour (Lawrence & Elphinstone, 2021). Conversely, marketers take a more lenient perspective and distinguish impulse buying from compulsive shopping, considering the former concept generally harmless and even benign . These opposing views result from the scarcity of research on the long-term consequences of impulse buying. Yet, extant literature mainly examined short-term and medium-term consequences of impulse buying, namely post-purchase emotions Togawa et al., 2019), customer loyalty Rao & Ko, 2021), word of mouth (Farah & Ramadan, 2020) and product return intention . As for long-term consequences, just a handful of studies examined coping strategies consumers adopt when dealing with postpurchase regret and guilt Spiteri Cornish, 2020).
Accordingly, future research needs to identify and examine other longterm consequences of impulse buying. For example, researchers can investigate the effect of hedonically rewarding online impulse purchases on the subjective well-being of consumers over time. Table 5 shows that impulse buying studies have predominately adopted quantitative research methods (162 out of 183 papers). Qualitative studies are extremely scarce in this research field, with just four articles identified by this review. Nevertheless, qualitative research is inductive and explorative and can effectively provide an in-depth understanding of an emerging phenomenon (Hoepfl, 1997;Van't Riet et al., 2001). For example, as the social commerce domain is still emerging, only a few antecedents of impulse buying specific to the social commerce environment have been identified (e.g., the influence of celebrities' social media posts).

| Methodologies
Thus, future research can adopt qualitative studies to explore novel factors influencing impulse buying in the social commerce context.
Further, mixed-method design has been overlooked in impulse buying research, with only five out of 183 studies adopting this approach. However, combining qualitative and quantitative data provides more insightful findings rather than using these methods individually (Hoepfl, 1997 In particular, the conceptual framework ( Figure 3) presented based on the synthesis of impulse buying literature suggested that store-related factors pertaining to online and offline shopping channels drive impulse buying. Notably, e-store design elements strongly influence impulse buying. Accordingly, online retailers should ensure that their web stores are easy to navigate and enjoyable to browse.
Seamless web store browsing leads to positive emotions, such as pleasure and flow experience, which prompt impulse buying. Hence, online retailers should make full use of e-store design, layout, and atmosphere. For example, providing customized product suggestions that include matching items and products bought by other shoppers can further boost online impulse purchases. Next, the checkout process during online shopping needs to be made easy for shoppers to conclude a purchase. For instance, web stores should allow for shopping without registration, tailor to shoppers' preferred payment methods and simplify the checkout steps to prevent consumers from changing their minds and abandoning the digital shopping cart.
The literature synthesis (i.e., the conceptual framework presented in Figure 3) also suggests that online peer influence predicts impulse buying in e-commerce. Hence, online reviews are an effective social influence tool in the marketer's arsenal. To increase impulse sales, online retailers can employ consumer reviews. For instance, online retailers can allow web shoppers to filter and categorize online reviews based on their preferences, such as showing the highest-rated and the most recent reviews. Further, e-retailers can allow for longer and more descriptive text in an online review and invite shoppers to use images and videos when sharing their experience with products.
Finally, this review identified the emergence of social and mobile commerce and their increased use by impulse shoppers, which can be an immense opportunity for marketers and retailers. E-retailers should utilize these trends and social networking sites to stimulate online impulse buying. Specifically, retailers can enhance their online presence on prominent social media platforms (e.g., Facebook and Instagram) and create interactive online content, increasing their reach and brand awareness.
To engage people browsing social media posts, marketing managers should use powerful online tools, such as likes, shares and comments on their posts and employ digital celebrities and social media influencers for endorsement. Further, retailers need to convert consumers' interest into actual sales by providing convenient direct product checkout on a social media platform or a direct link to the product page where the purchase can be completed. Moreover, mobile-friendly social commerce platforms can be used to maximize impulse purchases.

| CONCLUSION
This research effort has a few limitations that have to be acknowledged. This systematic literature review specified inclusion and exclusion criteria for selecting academic literature. Accordingly, the analysis and results of this review are restricted to articles that satisfy the defined criteria. Therefore, the findings cannot be generalized to the entire volume of impulse buying research. Further, this review considered papers written only in the English language. Therefore, studies conducted in other languages were out of the scope of this review.
Thus, these are the possible limitations of this review.
In conclusion, the purpose of this study was to systematically review

CONFLICT OF INTEREST
The authors declare no conflict of interest associated with this manuscript.

DATA AVAILABILITY STATEMENT
Data sharing is not applicable to this article as no new data were created or analyzed in this study.