The role of epidermal growth factor‐containing topical products on recovery and post‐inflammatory hyperpigmentation prevention after laser surgeries: A systematic review and meta‐analysis

Post‐inflammatory hyperpigmentation (PIH) is a common complication after laser surgeries. Recent studies applied epidermal growth factor (EGF) on the lasered area after laser surgery to decrease the incidence of PIH with controversial results. Therefore, a comprehensive literature review of randomized controlled trials (RCTs) was conducted to investigate the issue.

Post-inflammatory hyperpigmentation (PIH) is a reactive process of increased melanin and abnormal distribution of melanin which usually secondary to inflammatory skin disease, infections, allergic reactions, mechanical trauma, drug reactions, and phototoxic reactions, particularly in those with darker skin types. 1,2Recently, PIH has also become a major concern for patients undergoing laser treatment for cosmetic purposes.Laser treatments, such as fractional carbon dioxide (FrCO 2 ) and neodymium yttrium aluminum garnet (QS Nd: YAG) lasers, can cause damage to the basal cell layer, leading to PIH. 3 Studies have found that the incidence of PIH after 532/1064 nm QS Nd: YAG laser surgery ranged from 10% to 50% in Asian patients, 4,5 with FrCO 2 laser showing a higher occurrence rate of 95.8%. 6Once it occurs, PIH can persist for several months and have psychological impacts on patients. 7Thus, the prevention of PIH is crucial in the context of cosmetic laser treatments.
Several attempts have been addressed to the prevention of PIH after laser treatment.Previous research has shown the effectiveness of topical products containing several plant extracts and phytochemicals, hydroquinone, azelaic acid, kojic acid, retinoids, and corticosteroids in preventing PIH, but these can come with potential side effects including irritation, infections, contact dermatitis, and poor wound healing. 8,9More effective and safer drugs are needed to prevent PIH.Recently, some researchers applied EGF on the lasered area after laser surgery to decrease the occurrence of PIH and promote the wound healing process with controversial results.Therefore, a systematic review and meta-analysis were conducted to summarize the available evidence from the existing literatures.

| Data sources and searches
The review protocol for this study was registered with PROSPERO on June 4, 2023 (CRD 42023428403).Two independent reviewers independently conducted literature searches following the preferred reporting items for systematic reviews and meta-analyses guidelines.The databases searched included PubMed, Embase, the Cochrane Library, and the Web of Science.The search aimed to identify randomized controlled trials (RCTs) examining the role of EGF-containing topical products on recovery and prevention of PIH after laser therapy.The search encompassed articles published from the inception of the databases until June 2023.The search strategy combined keywords such as "laser," "epidermal growth factor," "EGF," "rhEGF," "post-inflammatory hyperpigmentation," "hyperpigmentation," and "pigmentation."

| Inclusion and exclusion criteria
Inclusion criteria for this review were as follows: (1) The search was limited to studies published in the English language involving clinical research conducted on humans.(2) The subjects of the studies were patients who underwent the same laser treatment.(3) In the study group, individuals received EGF-containing products after the laser procedure, while the control group received EGF-free agents.(4) The outcomes of interest included PIH, wound healing, or both.
The following types of studies were excluded from the review: (1) comments, patents, case reports, or reviews.(2) Studies that lacked necessary data and could not be concluded by reaching out to corresponding authors or using available data.(3) Research that did not involve human subjects.These criteria were applied to ensure that only relevant and valid studies were included in the review.

| Data collection
The titles, abstracts, and full text of studies in the retrieved literatures were screened to determine whether they fulfilled our selection criteria.Two authors independently extracted the data from the eligible studies and discussed these with a third author in cases of disagreement.Information recorded included study ID, research type, country, Fitzpatrick type, laser parameters, detection instrument, follow-up interval, sex, and age of the EGF and control groups, etc.The incidence of PIH in each group was collected to evaluate the effect of PIH prevention.Melanin index (MI) variations were extracted for subgroup analysis for investigating dynamic changes of the pigment.Wound healing process was determined subjectively by erythema index (EI) and trans-epidermal water loss (TEWL) which represented skin barrier function.Subjective measurement was the satisfactory score of the patients.

| Statistical analysis
The Review Manager software, version 5.3, was used to statistically analyze all data.The pooled odds ratios (ORs) and 95% confidence intervals (CIs) of the incidence of PIH in both groups were calculated.For continuous data such as variations of MI, EI, TWEL, and patients' satisfactory scores, the standard mean difference (SMD) was used if outcomes were comparable.Heterogeneity among the included studies was assessed using p and I 2 .The Mantel-Haenszel (M-H) fixed-effect model was used for studies without heterogeneity (p > 0.1, I 2 ≤ 50%), and a random effect model was used for studies that showed significant heterogeneity (p ≤ 0.1, I 2 > 50%).A p value <0.05 was considered statistically significant.

| Quality assessment
The quality assessment was performed based on the Cochrane Risk assessment tool to assess the risk of bias for each study by two independent authors.The assessment tool was used to evaluate the validity of the included studies according to criteria including random sequence creation, allocation concealment, blinding, insufficient data, selective reporting, and other biases.Each bias was rated low, unclear, and high risk.Inconsistencies were resolved through discussion.

| Literature search
A total of 128 studies were identified from four databases.Duplicate studies, reviews, case reports, patents, and other irrelevant articles were excluded after screening the titles and abstracts.Upon further review, seven literatures fulfilled the eligibility criteria.Figure 1 shows the flow chart of literature screening.

| Study characteristics
A total of seven studies were included, of which five were split-face self-RCTs and two were RCTs involving different individuals.The study population was derived from Korea and Thailand, specifically targeting individuals with Fitzpatrick skin types III-V.A total of 169 participants were involved in the analysis, with 85 individuals experiencing pigmentary disorders, 64 with atrophic scars, and 20 with wrinkles.Among the participants, approximately 79.9% were women.Patients in the EGF groups and controls were comparable before laser treatment.Detailed characteristics of the included studies can be found in Table 1 of the review.

| The incidence of PIH
Five of seven studies report the incidence of PIH after the laser surgery in both the EGF group and the control group.PIH in four of five studies was assessed on 8 weeks after the laser, while one study was assessed on 35 days.Marked heterogeneity (p = 0.12, I 2 = 45%) was observed across these studies; therefore, a M-H fixed-effect model was used.The pooled data showed that there was no significant difference in both groups (OR 0.64, 95% CI 0.33 ~ 1.25, p = 0.19; shown in Figure 2).Subgroup analysis of different laser modalities was conducted to investigate the effect on PIH prevention.The outcome revealed no statistically significant difference between QS Nd: YAG laser (OR 0.49, 95% CI 0.21 ~ 1.15, p = 0.10; shown in Figure 3) and FrCO 2 laser (OR 1.00, 95% CI 0.34 ~ 2.98, p = 1.00; shown in Figure 3).

| Patients' satisfactory
The analysis of patients' satisfaction scores using Visual Analogue Scales (VAS) showed low heterogeneity across the studies (p = 0.10, I 2 = 48%).Therefore, a M-H fixed-effect model was used.The results demonstrated that the overall satisfaction scores in the EGF group were significantly higher than that in the control group (SMD 0.49, 95% CI 0.22 ~ 0.76, p = 0.0004; shown in Figure 4).

F I G U R E 1
The flow chart of literature screening.Abbreviations: MGF, multigrowth factor-containing cream; NA, not available.

| Changes in MI
The meta-analysis of two studies reported no significant difference in MI variations between the EGF groups and control groups at week 2 after laser therapy (SMD 0.01, 95% CI −0.40 ~ 0.43, p = 0.95, Figure 5A).However, the result of four studies showed that at month 1 after therapy, the EGF groups had a significant

| Changes in EI and TWEL
The pooled data of three studies reporting EI variations at day 3 after laser surgery did not find a significant difference between the EGF groups and the controls (SMD 0.05, 95% CI −0.83 ~ 0.93, p = 0.91, Figure 6A).Similarly, the analysis of two studies reporting EI variations at day 7 also did not show any significant difference between two groups (SMD 0.17, 95% CI −0.26 ~ 0.60, p = 0.44, Figure 6B).
The analysis of two studies reporting TWEL variations at 3 and 7 days after laser therapy did not indicate a statistical difference between the EGF groups and the controls.No significant difference was observed on the 3rd day after laser therapy (SMD −0.40, 95% CI −0.83 ~ 0.04, p = 0.07, Figure 7A), as well as on the 7th day after laser therapy (SMD −1.57, 95% CI −4.24 ~ 1.11, p = 0.25; Figure 7B).

| Risk of bias assessment
Figure 8 shows the quality rating of the seven included studies.The color green indicates a low risk of bias, while yellow indicates an unclear risk.In this case, five studies did not describe random sequence generation, two studies did not illustrate allocation concealment, and four studies did not provide information on blinding of participants.No high-risk studies were identified.

| DISCUSS ION
This meta-analysis included a total of seven RCTs involving 169 patients to assess the effectiveness of EGF on recovery and prevention of PIH after laser treatment.The results showed that the incidence of PIH in the EGF group was lower than that in the control group, although the difference was not statistically significant.However, at the 1st month after the laser, the patients on the EGF side had a significant decrease in MI.In addition, the patients on the EGF side rated significantly higher satisfactory scores.There was no significant difference as regard to changes in MI at the 2nd week and 2nd month, EI, and TEWL at days 3 and 7 between the two groups, respectively.The use of FrCO 2 and QS Nd: YAG lasers did not show a significant difference in preventing PIH.
The QS Nd: YAG laser, which is based on the selective photothermal hypothesis, allows laser light to enter the dermis, absorb energy, and selectively remove melanin. 16While the FrCO 2 laser targets water and therefore might cause more damage compared to the QS Nd: YAG lasers.However, both FrCO 2 and QS Nd: YAG lasers may cause PIH. 17 Inflammatory mediators produced by laser-induced keratinocyte injury include prostaglandin D2, thromboxane B2, leukotriene C4, prostaglandin E2, leukotriene D4, leukotriene E4, and leukotriene B4, etc., can expand the volume of melanocytes, increase the number of melanocyte dendrites, enhance tyrosinase activity, and stimulate melanogenesis. 1,18In addition, lasers can induce heat in the epidermis and thus cause pigment dispersion, which is Recently, researchers have explored the application of topical anti-pigmentation agents to reduce PIH incidence after laser surgery.
According to research findings, hydroquinone, retinoic acid, corticosteroids, and tranexamic acid were effective in preventing PIH by inhibiting melanogenesis and melanosome transfer, increasing keratinocyte turnover, anti-inflammatory and anti-oxidative effects.
However, it is important to note that these agents may also have potential side effects such as additional inflammatory response which resulting in poor wound healing. 8,9Epidermal growth factor is an important regulatory mediator secreted by platelets, macrophages, and fibroblasts.Recent researches highlights the action of EGF on the melanogenesis. 19A cell experiment by Yun et al. 18 suggested that EGF reduced melanogenesis in conditioned medium of laser-treated keratinocytes, possibly by affecting prostaglandin E2 expression and tyrosinase activity.Additionally, the reduction of pro-inflammatory cytokines and the antioxidant effect of EGF may contribute to its anti-melanogenesis properties. 20Lyons et al. 21conducted a study where topical EGF serum was applied twice a day for 8 weeks, resulting in a decrease in melasma in 73.4% of cases without any reported side effects.These findings suggest that EGF could have played a role in reducing melanin production associated with hyperpigmentation.
The evaluation of PIH can be done using the MI, which measures the difference in absorption between melanin and hemoglobin at specific wavelengths. 22In this study, the PIH assessments of the included literatures were all performed at 7 ~ 8 weeks after surgery, and we observed no significant difference between two groups, which was consistent with MI variations at the 2nd month after the laser.However, we noticed a significant decrease in MI at the 1st month after the laser, which suggested the application of an EGF-containing cream had a significant inhibitory effect on MI at the 1st month following the laser procedure.This timeframe aligns with the peak occurrence of PIH in clinical practice.Research conducted by Chen et al. 23 demonstrated that the highest occurrence of PIH was reported 1 month after laser treatment, with most cases resolving within 6 months.A recent meta-analysis by Feng et al.   investigating the effects of tranexamic acid in addition to laser treatment showed similar results, where the inhibitory effect on melanin, as measured by MI, was notable at week 4.However, decreases in MI scores were not as apparent at months 2, 3, and 6. 24 Epidermal growth factor also plays a crucial role in promoting the proliferation and migration of keratinocytes in the process of dermal wound healing. 10Researches have been confirmed the efficacy of EGF to accelerate acute wound healing such as superficial seconddegree burn wounds, traumata, and surgical wounds. 25However, we observed no significant improvement with regard to post-laser EI and TWEL, which are recognized as one of the accurate and noninvasive methods to monitor skin wound healing. 26The assumption was that the vehicle used in most studies has high viscosity, which may affect the delivery of EGF into the wound columns. 14A study by Olesen et al. 27 showed a greater degree of microscopic treatment zones filling in the liquid form compared to gel and cream formulations after FrCO 2. In addition, topically applied EGF may diffuse rapidly from the site of injury, making it difficult to reach therapeutically relevant concentrations in the wound environment. 28Recently, the use of more effective biomaterials to deliver EGF has been recommended.Kim et al. 29  This study has several limitations.Firstly, the small sample size is one of the main drawbacks of this research.Secondly, there were marked heterogeneities between the groups in terms of the underlying disease and the laser wavelengths used.These variations may have influenced the outcomes and introduced additional sources of bias.
Furthermore, the follow-up time across the included studies was inconsistent, and most of them had insufficient evaluation periods.This limits our understanding of the long-term effects of the EGF on recovery and PIH prevention after laser treatments.Given these limitations, it is important to interpret the results with caution.Further prospective RCTs with larger sample sizes, rigorous methodologies, and longer follow-up periods are needed to definitively establish the issue.

| CON CLUS ION
The meta-analysis found a limited temporary inhibitory effect of EGF-containing topical products on PIH, with no significant effect on reducing post-laser erythema and promoting epidermal barrier repair.Further studies with larger sample sizes and rigorous methodologies are required to investigate the role of EGF in PIH prevention and alleviating the adverse effects of laser surgery.

DATA AVA I L A B I L I T Y S TAT E M E N T
The data that support the findings of this study are available from the corresponding author upon reasonable request.

E TH I C S S TATEM ENT
The review protocol for this study was registered with PROSPERO on June 4, 2023 (CRD 42023428403).All analyses were based on previous published studies, thus no ethical approval and patient con- decrease in MI scores compared to the control groups (SMD −1.57, 95% CI −2.83 ~ −0.31, p = 0.01, Figure 5B).At month 2, based on three studies, no significant difference in MI variations was observed between the two groups (SMD −0.62, 95% CI −1.76 ~ 0.53, p = 0.29; Figure 5C).

F I G U R E 2
Forest plot comparing the incidence of PIH after laser surgeries between EGF and control groups.F I G U R E 3 Subgroup analysis between QS Nd: YAG and FrCO 2 lasers.F I G U R E 4 Forest plot comparing the VAS of satisfactory scores at last visit between EGF and control treatment after laser surgery.| 387 YING et al.

F I G U R E 5
Forest plot compares the MI variations between EGF and control treatment at (A) week 2, (B) month 1, and (C) month 2. F I G U R E 6 Forest plot compares the EI variations between EGF and control treatment at (A) days 3 and (B) 7. F I G U R E 7 Forest plot compares the TWEL variations between EGF and control treatment at (A) days 3 and (B) 7. F I G U R E 8 Risk of bias summery of the seven included studies.| 389 YING et al. more commonly occurs in darker skin types.Our result of subgroup analysis also indicated no significant difference in the prevention of PIH between FrCO 2 and QS Nd: YAG laser modes.
employed the conjugation of EGF to hyaluronate, which resulted in delayed degradation and prolonged retention time of EGF, leading to significant improvements in skin tissue regeneration in the wound area.Altuntas et al. 30 utilized nanopillar chitosan-gelatin films for the topical delivery of EGF, which resulted in considerable improvements in wound closure and collagen thickness.These studies highlight the potential of utilizing innovative biomaterials for enhanced EGF delivery and wound healing outcomes.

Included studies Country Study type Diagnosis of subjects Fitzpatrick skin types Laser surgery Topical treatment after laser detection instruments Follow-up interval patients' satisfaction Sample size Mean age (year)
The characteristics of included studies.