An absence of imperfections: A proposed framework for defining, assessing, and achieving skin glow

Skin glow is a subcomponent of skin quality. It has become entrenched in the cosmeceuticals and aesthetics lexicons as a synonym for health and youth, but is not well‐defined as a scientific metric.


| INTRODUC TI ON
Skin glow has become firmly entrenched in the cosmeceuticals and aesthetics lexicons as a synonym for health and youth.A recent survey identified radiance as the fifth most common skin quality issue encountered by aesthetics practitioners, 1 and others note patients' use of terms such as radiance and healthy, glowing skin when seeking improvements. 2Flawless skin is strongly related to emotional well-being-it can influence a person's confidence and how they interact with others. 2,3It also symbolizes overall health and attractiveness.Established research supports a strong correlation between a variety of skin traits including skin condition, [4][5][6][7][8] color homogeneity, 9,10 different types of skin reflection (matte, oily) 11,12 and others' perceptions of an individual's health and vitality.To the consumer, glow is perceived to represent health, attractiveness, and youth. 13spite an increasing focus on the concepts of "skin quality" and "radiance" in the literature, there is no universal terminology to define these concepts, primarily because they each rely on a combination of physiological (objective) and psychological (subjective) attributes.Skin quality has most frequently been defined in the context of aging and rejuvenation, encompassing several descriptive parameters that vary by age group. 2 To this point, a photonumeric scale for evaluating facial skin quality in older females, includes signs of aging (elasticity, firmness, and wrinkles), as well as color (pigmentation, redness) and surface changes (roughness, pore size, and blemishes). 14Independently of aging, a literature review has defined skin quality based on multiple components of its visible, mechanical, and topographical attributes. 2 An international consensus defined skin quality as a combination of evenness of skin tone, skin surface, skin firmness, and skin glow. 15Within both of these papers, skin glow was identified as a subcomponent of skin quality, but it was not objectively defined.Goldie et al. opined that skin glow does not have individual parameters and instead defined it by presenting a list of synonyms (radiance, luminosity, brightness, vibrancy, and complexion). 15While Humphrey et al. identify radiance and the ability of the skin to glow or reflect light, noting this to be attribute to the visible quality of the skin that is depend upon hydration levels and the amount of dead/dry skin accumulation blocking light reflection. 2 With regard to the measurement of skin glow, evaluation of skin tone, and radiance (surface gloss and absorption/reflection based on melanin and hemoglobin content, measured, respectively with a glossymeter and a mexameter [both Courage & Khazaka, Cologne, Germany]) has been suggested, 15 based on clinical findings from a clinical study assessing skin rejuvenation using hyaluronic acid filler. 16Others suggest simple visual analogue scales to report separate metrics for glow and radiance, 17 and some suggest the need to account for both visible reflection and hydration. 2,12 skin glow simply cosmetic jargon, a word chosen to convey a concept that has no scientific meaning, 18 or is it a tangible concept that can be defined and measured?We hypothesize that an improved understanding of skin glow from a more holistic perspective may help to better communicate with patients what it is, and, what treatment approaches are available to improve it.The aim of this work was therefore to examine the concept of skin glow, determine if it is an objective concept that can be defined and quantified, and then use these concepts to provide a guidance framework for assessment and treatment planning in the aesthetic clinic setting.

| ME THODS
A working group, comprising four dermatologists, two plastic surgeons, a cosmetic physician, and a maxillofacial surgeon, convened to discuss their current approaches to the assessment of four core domains-skin glow, lip aesthetics, lower eyelid aesthetics, and facial profile aesthetics.A literature search was undertaken, from which relevant data were used to inform the development of a practitioner survey.
The practitioner survey was designed to evaluate the experiences, perceptions, and opinions of a wider group of 40 invited aesthetic clinicians in the Asia-Pacific region and was completed electronically (February 2022).The survey tool comprised 37 custom-written questions.Of relevance to the skin glow domain there was one question regarding features contributing to general overall respondents reported routinely assessing skin quality, citing serial photography (83%), and visual inspection (67%) as the main means of achieving this.The focus group defined skin glow as even reflectance from an unaffected papillary and reticular dermal collagen layer, which is created only when skin does not exhibit any characteristics that detract from this even reflectance.Due to its complexity, the focus group proposed a hierarchal framework for assessment, encompassing patient self-rating, practitioner severity rating, and supplemental use of validated measurement devices.
Conclusions: Skin glow can be defined and quantified.More work is warranted to develop a practical skin glow assessment tool suitable for use in the clinic setting.

K E Y W O R D S
aesthetics, dermatologists, detractors, reflectance, skin glow aesthetic first impression and five questions specifically pertaining to skin glow.Response categories comprised fixed options, numerical rating scales (0 = no contribution, 10 = maximum contribution; higher scores equate to higher contribution), and ranking order (most important to least important; lower scores equate to higher importance).Only returned surveys with complete datasets were analyzed; data were summarized descriptively, and statistics performed using GraphPad Prism (GraphPad Software, LLC, Boston, MA, Version 9.3.1).
In March 2022, the authors convened in a hybrid in-person/online focus group meeting during which the authors shared their opinions on the characteristics of skin glow, best practice approaches to evaluating skin glow, and reached a consensus by majority vote (>90% in favor) on a definition of skin glow, its key components and methods of assessment.

| Responses to practitioner survey
The response rate to the practitioner survey was 98% (39/40), of which 38 contained complete datasets.Respondent demographics are summarized in Table S1.Skin quality was ranked as the fourth dermis, and subcutaneous tissue [hypodermis or superficial fat pads]) could impact overall skin quality.Additionally, one third (34%) agreed that the relative contribution of these different skin layers differed by age group, there was general agreement that the more superficial layers were of greater importance in younger age groups (20-30 years) and the deeper layers of more importance in older age groups (ε40 years).With regard to treatment choices, respondents highlighted collagen stimulators, skin boosters, neuromodulators, and laser based therapies as having the most contribution to overall skin quality improvement.When asked more specifically about the extent to which different characteristics might detract from skin glow, survey respondents reported acne, laxity, and pigmentation to be the most important, while shine and excess contrast the least important (Figure 1).Almost all (95%) respondents reported routinely assessing skin quality.Serial photography was the most frequently used assessment tool (83% of respondents) followed by visual inspection (67%).Reports of a moderate level of use of the pinch (50% of respondents) and snap (44% of respondents) tests correlated well with lack of laxity being identified as a key detractor from skin glow.(spring), and "glow" as has previously been proposed. 15There was also agreement within the focus group that reflection was integral to the glow. 2 The skin is a semitransparent medium that absorbs and scatters light (radiation). 19Skin radiance is defined in terms of the quantity of light reflected from it by measuring parameters such as diffusion, reflectance, and speculation. 20When light hits the skin surface it reflects in many different directions.Even reflection takes place when light reflects off a smooth surface such as youthful skin or skin to which moisturizer or make-up has been applied.The skin surface may contribute to an alteration of optimal reflection by dispersion in the case of excessively dry skin or an exaggerated surface reflection from the slick of oily skin.However, skin glow is affected by more than just the surface integrity of the skin.The appearance of the skin is determined by absorption of light (hemoglobin and melanin) and scattering of light is due to organic structures such as mitochondria and collagen fibers. 19,21The group agreed that the depth of the skin should also be considered because the dense collagen texture gives the reflection a halo-like glow.On this basis, they supported the concept that when there is an uninterrupted dermal light reflection in normal or rejuvenated tissue a milky homogenous appearance results from light bouncing of collagen, 9,10 and this also contributes to skin glow.It has previously been proposed that skin radiance (desired attribute) is associated with subsurface diffuse reflections whereas excess skin shine/gloss (undesirable attribute) is associated with specular surface reflections (excess sebum, oily skin). 22Others support the concept that skin radiance is defined by the quantification of both the speculation of light on the surface and diffusion of light from within. 12,23Skin glow therefore requires an optimal balance of surface reflection, diffuse reflection, and subsurface scattering. 24,25This concept is depicted schematically in Figure 2. 26 Having reviewed this information, focus group consensus was achieved on the following definition: The glow is even reflectance from an unaffected papillary dermal and possibly reticular dermal collagen layer and is created only when skin does not exhibit any of the characteristics that detract from this even reflectance.

| Skin attributes that detract from the glow
By definition, any attribute or factor that obscures the even reflectance of light from the skin would detract from the glow.The focus group considered the potential detractors that had been provided in the practitioner survey (Figure 1) and classified them by considering the layers of the skin from outside to inside in order of relevance to the interruption of the glow (Table 1).All layers were considered to be important, with consensus that the stratum corneum and then the papillary dermis were the dominant contributory skin layers.For example, sun damaged skin or a scarred dermis would create scattered light with a dull, sallow appearance, while oil on the surface of the skin would create diffuse, mildly, and heavily scattered light, all of which detract from the glow.There was consensus that the subcutaneous tissues (hypodermis or superficial fat pads) are of relevance to skin glow primarily in relation to laxity and the observation that stretching the skin would better enable an even reflection of light.
Considering patient age in relation to skin glow, the group agreed that while age can impact negatively on a person's appearance, chronological age per se does not reduce the glow.Instead, the overall number of factors that can detract from achieving an unobscured dermal surface increases with age as a result of intrinsic aging and extrinsic sun damage.For example, in older patients there would likely be more contributing factors in the dermis as a result of intrinsic and extrinsic aging, in particular sallowness, skin thinning, seborrheic keratoses, entrenched expression lines (observed at rest), and wrinkles, blood vessels, lentigines, and solar elastosis with associated degradation of elastin and collagen fibers.By comparison, factors such as skin sensitivity, expression lines, acne, scars, pore size, pigmentation, oiliness, and dryness, which are not related to extrinsic skin damage, could negatively impact skin glow irrespective of age (Table 1).
Established research demonstrates that while surface topography (wrinkles) drives facial age perception, color evenness is most closely associated with health perception supporting that evenness of color vastly improves the perception of skin glow. 5,10Having viewed a patient case study, the focus group observed that removing erythema resulted in color evenness, with a perceived associated increase in health perception and skin glow (Figure 3).Uneven melanin production from basal layer melanocytes in the dermal/epidermal junction creates a veil of pigmentation on the surface of the skin detracting from what is underneath it, reducing dermal reflectance and obscuring the glow.In a similar way, actinic and seborrheic keratoses, characterized by thickened, raised patches of sun damaged skin, cause scattering of light that obscures the glow.Skin contrast is one of the keys to perceiving skin health and contrast enhancement by skin irregularities, such as lumps, bumps, pores, and wrinkles, distorts the evenness of light reflectance.For example, open pores interrupt the smoothness of the skin, causing the light reflection to be broken up as it bounces off the dilated holes (Figure 4).[29][30][31]

| Assessment framework
After discussion, there was consensus that 15 detractors could contribute to skin glow, and that these detractors could be grouped under different categories-skin type, evenness of color, surface imperfections, and general dermal health characteristics (Table 2).
The underlying concept of a skin glow assessment is to identify the patient's concerns and enable an objective practitioner evaluation, while being sensitive enough to document pre-and post-treatment changes.A secondary purpose of such an assessment would be to help educate the patient as to the detractors that can lead to reduced skin glow and better communicate the benefits of different treatment strategies.
However, because so many characteristics can interfere with the glow, it was determined that a simple photonumeric scale would not suffice and that a hierarchal algorithm would be of more value.There was consensus that use of an established systematic facial assessment, such as the global ranking scale, 32 could be used initially to help to determine if skin glow was a priority issue for the patient.This facial assessment tool includes a number of metrics, one of which is the extent to which the patient is concerned about "loss of radiance/glow."If the customer were to rate loss of radiance/glow highly, then this would prompt a more detailed skin glow assessment (Figure 5).
The focus group reached consensus that within this framework an initial patient assessment should use a simple visual analogue scale, with photographic imagery, to enable the patient to self-identify their current perception of skin glow (Figure 5, step 1).This should then be followed by a detailed visual practitioner assessment F I G U R E 2 Schematic depiction supporting the concept that skin glow requires an optimal balance of both surface reflection and subsurface reflection.Adapted from Dahlan et al., 26 Image credit: https:// www.shutt ersto ck.com/ 11904 38494 TA B L E 1 Order of priority of skin layers and associated attributes that detract from skin glow.(Figure 5, step 2).Utilizing a simple assessment scale to first determine the presence/absence of detractor characteristics and, where present, provide an indication of their severity grading (Table 2), could facilitate identification of the detractors that contribute most burden.
While serial photography is of established value in the aesthetic setting, it is not always optimal when trying to document the glow.
Where practicable, the group were in favor of supplementing the patient and practitioner assessment with the use of validated objective measurement devices to quantify color (Chromameter, Konica Minolta, Ramsey, NJ, USA) 33 and optical standardized cameras with software systems, such as the VISIA Complexion Analysis System (Canfield Imaging Systems, Fairfield, NJ, USA), to grade surface imperfections (spots, wrinkles, texture, pores), pigmentation (brown spots, redness), and aspects of dermal health (porphyrins/propensity for acne breakout). 34

| Treatment planning
Group consensus was that individualized treatment plans should be guided by the primary patient concern and practitioner assessment, irrespective of patient age.Having reached an understanding of which characteristics detract from the glow and how to assess them, the focus group then mapped each of these to the different skin layers and proposed an overview of potential treatment options that practitioners could call upon when planning treatment (Table 3).There was consensus that an integrated approach would

| DISCUSS ION
A simple Google search for "skin glow" returns over 1 billion hits.
Despite the ubiquity of its use, it means different things to different people.This paper attempts to provide some clarity.Using a combination of published literature, peer input, and expert collaboration we determine that skin glow is a tangible, measurable concept.Skin glow has been identified as a sub-component of skin quality, 2,15 and radiance is used to describe outward perceptions of health and vitality. 35We propose that skin glow is created by an uninterrupted dermal light reflection (perceived radiance) bouncing off homogenous skin that is free from detractors.
Early attempts at defining skin radiance via mathematical modeling identified a number of skin surface reflection parameters (luminosity, color variation/saturation, and surface irregularities) skin). 36Studies utilizing optic imaging tools quantified skin radiance in terms of the quantity of light reflected from it by measuring parameters such as diffusion, reflectance, and speculation. 20suda et al., defined skin radiance as the quantification of speculation of light on the surface and diffusion of light from within. 12,23hers have proposed that radiance is a combination of surface and subsurface reflections, requiring an optimal balance of both surface reflection (shine), and subsurface reflection (low melanin content/fairness). 24These findings correlate with recent research demonstrating that attractiveness ratings were highest in subjects with radiant skin, where radiance was defined as "a specific type of facial reflection". 11,12Most recently, an algorithmic approach accounting for surface reflection, diffuse reflection, and subsurface scattering has been developed to measure the optical properties of facial skin and quantify age-related changes in terms of a luminance value. 25These optical properties have been directly related to the condition of different functional components of the skin (melanin, hemoglobin, and collagen) at different layers and to the perception of qualities such as its gloss, dullness, and translucence. 25r definition of skin glow is based on an appraisal of a series of detractors at different layers of the skin.Established aspects of skin quality, such as uneven color, surface imperfections, dermal conditions, and excess oiliness or dryness interrupt reflectance, such that skin glow can occur only in the absence of these detractors.

TA B L E 3
Treatment options that could be used to target "glow detractors" at different skin layers.

Skin layer Glow detractors Therapies to target detractors a
Stratum corneum We propose that systematic assessment of each of these glow detractors using a 0-4 rating scale could enable a simple numerical quantification of their presence and their burden, providing a personal patient profile.Achieving skin glow is important to patients, 1,2 but it is poorly defined and may mean different things to different people.An assessment tool would enable aesthetics practitioners and dermatologists to better define the components that contribute to skin glow and establish a common understanding of this with their customers when assessing their concerns and planning treatments.
Skin glow is not a single entity that can be managed with a simple one-treatment-fits-all solution.Holistic assessment, as has been proposed in the framework, leads to an understanding of the key drivers for each patient, which can then be addressed via an individualized treatment plan.For example, where such assessment identifies detractors associated with intrinsic aging (e.g., laxity, volume loss, collagen depletion 37 ), rejuvenation strategies would be the primary focus of the treatment plan.Dermal fillers in this layer can be used to create volume, convexity, and stretch the skin, which may improve surface reflectance and thereby contribute to enhanced glow.
However, in older patients, thin, loose skin creates a challenge for the use of dermal fillers.Improving other aspects of skin quality first may enable the skin to be prepared for hyaluronic acid-based fillers and has the added benefit of subsequently reducing the amount of filler required to achieve the desired results.In such cases injectable collagen stimulators, such as poly-L-lactic acid, induce natural collagen production, and can be used to restore facial volume over time. 38Consensus guidelines on the use of collagen stimulators for minimally invasive aesthetic treatment of the face have been published. 39In younger patients, where the vitality of the skin is still present, injection of stabilized hyaluronic acid into the subdermal layer can be used to restore hydration, soften dynamic and static lines, and improve skin surface texture without adding volume. 40In contrast, if the assessment identifies detractors associated with environmental factors (e.g., smoking, stress, diet/sugar consumption, UV, and blue light 41 ) strategies would be primarily focused on reducing this environmental burden, and could include energy-based devices, 42 and chemo-exfoliation to reduce actinic damage, lentigos, and dyschromias. 43e current work is limited in that it provides only the starting point for the development of a definition and metrics for assessing skin glow.In the practice setting, use of an initial global assessment tool has been demonstrated help to identify the core patient concerns. 32We propose that if patients identify skin glow, or perceptions of skin health, as their main concern then they should be offered a tailored assessment that focuses more specifically on the glow detractors (Step 2 in our framework; Figure 5).Given the widespread use of serial photography in clinical aesthetics practices, and the availability of newly proposed mathematical algorithms, 25 future considerations for implementation of such an assessment framework could include the development of an integrated "Skin Glow" app with in-built photonumeric scales for each of the glow detractors.The future development of a patient-reported quality of life index could be used to provide the practitioner with feedback pre and posttreatment, which would be of particular value given the impact of skin appearance on perceptions of health and wellbeing.
In conclusion, skin glow can be defined and quantified based on

FU N D I N G S TATEM ENT
This work was funded through an educational grant provided by Galderma Australia Pty Ltd.The authors were responsible for all content, interpretation of the data, and the decision to publish the results; they received no honoraria related to the development of this manuscript.

CO N FLI C T O F I NTER E S T S TATEM ENT
Tara Telfer is an employee of Galderma Australia Pty Ltd.The remaining authors declared no potential conflicts of interest with respect to the research, authorship, and publication of this article.
most important factor related to a person's overall aesthetic first impression (ranking score 5.29), after facial proportions (3.34), facial shape (3.84), and facial contours (4.11).A majority of survey respondents (79%) indicated that all skin layers (stratum corneum, superficial layers of the epidermis, deeper epidermis [dermoepidermal junction], The focus group first considered the wider concept of what beauty means to a consumer.They agreed that beauty is represented by volume in the right places on the face and body, to give it shape and highlight its key features, and by the way a person moves and the expressions they make.With specific reference to skin quality, the group agreed it encompasses evenness of color, texture, firmness F I G U R E 1 Survey respondents' ranking of the contribution of potential factors that detract from skin glow.

F I G U R E 3 F I G U R E 4
Erythema, health perception, and skin glow.Features such as open pores create contrast, breaking reflectance and detracting from the glow.be of most benefit.Such a treatment plan could include a baseline of daily skincare to remove dirt and makeup, hydrate and protect, specialist skincare regimens incorporating cosmeceuticals to address specific dermatological conditions, and in-office skin and aesthetic treatments.

TA B L E 2 • 5
Assessment scale to identify core glow detractors.Disease states (e.g., eczema, periorificial dermatitis, seborrheic dermatitis, psoriasis) Schematic of key steps in a detailed assessment of the glow.Image credit: https:// www.shutt ersto ck.com/ 12162 52057 but failed to capture subjective descriptors (e.g., transparent the presence and severity of detractors that affect the reflection of light in multiple layers of the skin.The proposed systematic assessment framework for use in the clinic setting, incorporates patient and practitioner input, and, where practicable, utilizes validated objective measurement tools.Further work is warranted to develop this concept into a practical skin glow assessment tool suitable for use in the clinic setting, Such an assessment tool could be used to identify and rate the severity of multiple skin glow detractors.Defining and formally assessing skin glow in this way provides a means to help educate patients about its causes and tailor individual treatment plans.ACK N OWLED G M ENTS The authors thank the co-chairs of the Scientific Exchange Working Group for their input into the early stages of this work, including the development and analysis of the practitioner survey.The authors thank Hazel Palmer MSc, ISMPP CMPP™ of Scriptix Pty Ltd, for providing administrative support, professional writing assistance and editorial support in the preparation of this manuscript, which, in accordance with Good Publication Practice guidelines, was funded through an educational grant provided by Galderma Australia Pty Ltd.Open access publishing facilitated by Monash University, as part of the Wiley -Monash University agreement via the Council of Australian University Librarians.

Skin layer a Glow detractors Age related
1. Stratum corneum • Excess oiliness • Excess dryness • Actinic and seborrheic keratoses • Skin conditions: Dry (excess squames, faulty desquamation)a Order of priority was determined by consensus voting, where 1 = highest priority and 5 = lowest priority with respect to skin glow.
Treatment suggestions are based on the opinions of the focus group. a