Synergistic effects of long-wavelength ultraviolet A1 and visible light on pigmentation and erythema.

BACKGROUND: Visible light (VL) induces multiple cutaneous effects. Sunscreen testing protocols recommended by regulatory bodies throughout the world require the use of solar simulators with spectral output in the ultraviolet (UV) domain only. However, sunlight contains VL and infrared radiation also. OBJECTIVES: This study aimed to evaluate the contributions of VL and UVA on pigmentation and erythema, and optimize parameters for in vivo testing. METHODS: Ten subjects with Fitzpatrick skin phototype IV-VI were enrolled. Subjects were irradiated on their back with VL using two light sources: one containing pure VL and one containing VL with less than 0·5% UVA1 (VL+UVA1). Four different irradiances were administered to investigate reciprocity behaviour. Assessments, including photography, Investigator's Global Assessment, colorimetry and spectroscopy, were performed immediately, 24 h, 7 days and 14 days post-irradiation. RESULTS: Pigmentation was observed with both light sources; however, pigment intensity was greater with VL+UVA1 than with pure VL. Reciprocity was observed in pure VL sites, but not VL+UVA1. Variation in spectral output had greater impact on pigment intensity than irradiance. Clinical erythema was observed on the VL+UVA1 side, but not on the pure VL side. A protocol for testing photoprotection product efficacy against VL-induced effects has been proposed. CONCLUSIONS: The findings suggest a synergistic relationship between VL and UVA1 and emphasize the need for developing means of photoprotection against VL.

Review of applications of fluorescence excitation spectroscopy to dermatology.

Endogenous molecules that exhibit fluorescence hold the potential to serve as reporters of tissue structure, activity and physiology. Fluorescence excitation spectroscopy is one means to measure and express tissue's innate fluorescence. This review focuses on the application of endogenous fluorescence ultraviolet excitation spectroscopy to dermatology.

Assessing facial wrinkles: automatic detection and quantification.

BACKGROUND: As people mature, their skin gradually presents lines, wrinkles, and folds that become more pronounced with time. Skin wrinkles are perceived as important cues in communicating information about the age of the person. Nowadays, documenting the facial appearance through imaging is prevalent in skin research, therefore detection and quantitative assessment of the degree of facial wrinkling can be a useful tool for establishing an objective baseline and for assessing benefits to facial appearance due to various dermatological treatments. However, few image-based algorithms for computationally assessing facial wrinkles are present in the literature, and those that exist have limited reliability. METHODS: In this work, an algorithm for automatic detection of facial wrinkles is developed, based on estimating the orientation and the frequency of elongated spatial features, captured via digital image filtering. RESULTS: The algorithm is tested against one set of clinically validated 11-point wrinkle scales present on the face. The algorithm is employed for assessing the presence of forehead furrows on a set of 100 clinically graded facial images. The proposed computational assessment correlates well with the corresponding clinical scores. CONCLUSION: We find that the results are in better agreement with clinical scoring when the wrinkle depth information, approximated via filter responses, is combined with the wrinkle length information as opposed to the case when the two measures are considered separately.

Caucasian facial L* shifts may communicate anti-ageing efficacy.

An ageing study was conducted to capture skin colour parameters in the CIELab system from Caucasians of both genders and all available adult ages. This study produced a linear correlation between L* and age for a Caucasian population between 20 and 59 years of age as follows: (L* value) = -0.13 × (Age in years) + 63.01. Previous studies have addressed age-related changes in skin colour. This work presents a novel consumer correlated quantitative linear model of skin brightness by which to communicate age-related changes. Two product assessment studies are also presented here, demonstrating the ability of anti-ageing products to deliver on objective and subjective improvements in skin brightness. It was determined to be possible to use the fundamental Caucasian L*-age correlation to describe product benefits in a novel quantitative and consumer-relevant fashion, through the depiction of a 'years back' calculation.

Infant skin physiology and development during the first years of life: a review of recent findings based on in vivo studies.

Infant skin is often presented as the cosmetic ideal for adults. However, compared to adult skin it seems to be more prone to develop certain pathological conditions, such as atopic dermatitis and irritant contact dermatitis. Therefore, understanding the physiology of healthy infant skin as a point of reference is of interest both from the cosmetic as well as from the clinical point of view. Clinical research on healthy infants is, however, limited because of ethical considerations of using invasive methods and therefore until recently data has been scarce. Technical innovations and the availability of non-invasive in vivo techniques, such as evaporimetry, electrical impedance measurement, in vivo video and confocal microscopy, and in vivo fibre-optic based spectroscopy, opened up the field of in vivo infant skin physiology research. Studies incorporating such methods have demonstrated that compared to adult, infant skin continues to develop during the first years of life. Specifically, infant skin appears to have thinner epidermis and stratum corneum (SC) as well as smaller corneocytes at least until the second year of life. The water-handling properties are not fully developed before the end of the first year and infant SC contains more water and less amounts of natural moisturizing factors. Such findings re-evaluate the old notions that skin is fully matured at birth. Armed with this knowledge, we are in a position not only to better understand infant dermatological conditions but also to design better skin care products respecting the distinct qualities of infant skin.

Documentation of normal stratum corneum scaling in an average population: features of differences among age, ethnicity and body site.

BACKGROUND: Scaling skin involves an imbalance between cell proliferation and desquamation, resulting in partially detached corneocytes at the stratum corneum (SC) surface that become visible as they scatter light. OBJECTIVES: The purpose of this study was to document scaling skin with no associated pathology, to estimate the range of normal corneocyte detachment in the average population, and to determine if age, pigmentation and/or body sites of different exposures contribute to differences observed in the SC. METHODS: Healthy African-American and Caucasian female subjects (n = 151) from a typical central New Jersey population, aged between 14 and 75 years, were evaluated on the dorsal forearm and upper inner arm. Dermatoscopy and adhesive tape were used to evaluate the appearance and adhesion of surface corneocytes. Transepidermal water loss and conductivity were measured to assess water-handling properties of the SC. Measurements were conducted during the winter. RESULTS: Corneocyte detachment observed with dermatoscopy became more prevalent with age and was more severe on the dorsal forearm and in Caucasian subjects. The distribution of the amount of corneocyte removal with adhesive tape increased with age. The range of values was larger in the dorsal forearm than the upper inner arm and was greater in Caucasian subjects than African-American subjects. Minimal changes were observed for water-handling properties. CONCLUSIONS: The architecture of the outer SC appears different between ages, body sites of different exposures, and individuals of different pigmentation groups, but minimal differences in water-handling properties are observed.

Measurement of skin texture through polarization imaging.

BACKGROUND: Determination of skin surface texture is of particular importance in the field of dermatology as such measurements can be used for skin diagnostics and evaluation of therapeutic or cosmetic treatments. Profilometry of skin replicas, three-dimensional imaging and computer vision have been successfully used to measure and document skin texture. Nevertheless, the development of a simpler and faster technique may prove to be advantageous in a clinical setting. OBJECTIVES: We propose the use of polarization imaging with high angles of incidence as a simple alternative to measure/document skin texture/roughness. METHODS: A system based on digital photography and polarization optics was developed to acquire and compute texture images. Optimization of the system configuration was conducted to enhance the contrast for measuring skin roughness. The method was validated against roughness standards and tested in clinical studies. Measurements were made in subjects aged from 9 to 70 years and image analysis was used to evaluate texture. RESULTS: The developed texture scale was shown to correlate closely to the results from clinical assessment and from roughness standards. Frequency domain analysis showed a significantly different power spectrum for the texture images of young subjects when compared with older subjects. The evaluation of texture as a function of age showed that facial skin roughness increased linearly from teenage to 40 years followed by a plateau thereafter. CONCLUSIONS: The system proved to be a useful clinical tool for assessing skin texture. The age-related results may indicate that some skin texture features are formed before the age of 40 years.

In vivo measurement of skin erythema and pigmentation: new means of implementation of diffuse reflectance spectroscopy with a commercial instrument.

BACKGROUND: Various physical, chemical and biological insults, including exposure to ultraviolet (UV) radiation, cause erythema and change in pigmentation in human skin. These reactions provide an important measure of the cutaneous response to the insult. OBJECTIVES: To present a new implementation of a method for objective in vivo measurement of erythema and pigmentation. METHODS: The method is based on acquisition of reflectance spectra in the visible range using a commercially available spectrophotometer. The probe of this instrument incorporates an integrating sphere that captures the light remitted from the skin in a wide range of angles. We corrected the acquired reflectance spectra for the contribution of specular reflections by an amount given by the Fresnel equation and verified this correction experimentally. This correction is particularly important when measurements are performed on heavily pigmented skin. The corrected reflectance spectra are then transformed into absorbance spectra. To analyse these spectra, we developed an algorithm which can be used to calculate apparent concentrations of oxyhaemoglobin, deoxyhaemoglobin and melanin. This method was tested in clinical studies of skin reactions induced by exposure to UV radiation. These experiments involved three groups of subjects with progressively darker complexion (constitutive pigmentation). Each group consisted of 10 subjects. Erythema was measured 1 day after UV exposure, and pigmentation (melanin content) 1 week later. Results Distinct apparent absorbance spectra were obtained for dark, intermediate and fair skin. There was good agreement between reconstructed spectra and experimental data at relevant wavelengths. Difference absorption spectra were able to show the dose dependence of UV-induced responses, and erythema and pigmentation values obtained by the spectroscopic method showed good correlation with those derived by subjective visual grading. CONCLUSIONS: The results demonstrate that the presented methodology provides an objective noninvasive way of measuring UV-induced reactions independently of the level of constitutive pigmentation.

Skin viscoelasticity displays site- and age-dependent angular anisotropy.

One of the dominant characteristics of skin aging is loss of elasticity. Although the changes in the mechanical properties of the skin over several decades of life are substantial, objective measurements have failed to capture their magnitude thus far. Moreover, the mechanical properties of the skin are not uniform in all directions, and there is a need to understand this angular anisotropy. In this work we present a methodology of documenting the angular anisotropy of skin elasticity with high sensitivity and dynamic range using the Reviscometer RVM 600 (Courage & Khazaka Electronic GmbH, Cologne, Germany). The method is based on determining the directional dependence of the speed of an acoustic shear wave on the skin surface at intervals of 3 degrees . Based on the angular distribution of the resonance running time, we define two parameters: the anisotropy and the angular dispersion width. We find that with increasing age the anisotropy increases, while the angular dispersion width decreases. The ratio of these values provides a sensitive parameter for the assessment of the directional behavior of the skin mechanical properties. This parameter provides a large effective dynamic range capable of demonstrating close to an order of magnitude differences in skin viscoelasticity from infants up to adults 75 years of age. Furthermore, we show that the direction of the angular anisotropy relates to the direction of the dermal cleavage lines as defined by Langer, indicating that the anisotropy of the mechanical properties of skin stems from structural parameters. Based on these results, we conclude that the proposed methodology is able to capture accurately the age-dependent changes of the mechanical properties of the skin and to demonstrate a structure-function relationship.

Facial skin fluorescence as a marker of the skin's response to chronic environmental insults and its dependence on age.

BACKGROUND: Throughout life facial skin is exposed to a variety of adverse environmental conditions and is constantly required to repair itself. The rate of epidermal cell proliferation is indicative of the skin's repair rate and can be monitored noninvasively in vivo using skin intrinsic fluorescence markers. OBJECTIVES: The goal of the present study was to assess the effects of ageing, geographical region, ethnic origin and season on the ability of facial skin to repair itself in the presence of chronic environmental insults using in vivo fluorescence spectroscopy. METHODS: Skin fluorescence emission was measured on the cheeks of 522 individuals in winter and repeated in summer in five different geographical locations in the Asia-Pacific region. Fluorescence emission was also measured from 80 caucasians of fair complexion in the United States (New Jersey area) on the face and on a relatively protected area (upper inner arm). The age range of the participants was 14-75 years. RESULTS: We found that epidermal proliferation rates decrease monotonically with age, while the fluorescence of collagen and elastin cross-links increases with age indicating accumulation of advanced glycation end-products. These trends were independent of geographical region, ethnic origin and season of measurement. Epidermal proliferation rates of facial skin were higher than those of unexposed sites; they may be 10 times higher in younger (second decade) than in older (seventh decade) individuals, and they decrease with age at rates 10 times faster compared with those of unexposed sites. CONCLUSIONS: This is the first time that epidermal proliferation and its dependence on ageing have been measured noninvasively on the human face. The higher tryptophan fluorescence values on the face vs. the protected site are indicative of accelerated rates of epidermal proliferation in the presence of chronic environmental insults. The repair potential of facial skin, i.e. its ability to maintain high proliferation rates, is maximal in younger populations and gradually decreases with age.

Evaluation of peripheral arterial occlusive disease and postsurgical viability using reflectance spectroscopy of skin.

HYPOTHESIS: Stress-induced changes in skin microcirculation allow staging of peripheral arterial vascular pathology using diffuse reflectance spectroscopy (DRS) of the skin. DESIGN AND METHODS: The changes in relative concentration of oxyhemoglobin and deoxyhemoglobin in the cutaneous microvasculature were assessed at rest, during limb elevation, dependency, and cuff-mediated reactive hyperemia for the forearm of 25 normal subjects and 105 feet of patients with peripheral arterial occlusive disease (PAOD) (normal=28, claudication=34, limb threatening ischemia=44). Thirty-four patients who had revascularization procedures were again evaluated within the first week postoperatively. RESULTS: Two measurements correlated with clinical staging: (1) the relative absorbance of oxyhemoglobin after 225 s of limb dependency and (2) the time to reach 50% of peak reactive hyperemia response (Spearman's rank: rs=0.625, P<0.001). Using these criteria alone, ischemic limbs were identified to a sensitivity of 69% and specificity of 95%. Significant post-revascularization improvement was identified in 14 of 34 patients' legs which had previously been classified as limb-threatening ischemia (n=14, W=105, P<0.001). CONCLUSIONS: These simple bedside evaluations of the superficial skin microvasculature allow staging of large vessel vascular insufficiency and may suggest and differentiate focal areas of tissue at risk for ulceration or necrosis.

Non-invasive in vivo determination of UVA efficacy of sunscreens using diffuse reflectance spectroscopy.

BACKGROUND: Evaluation of sunscreen efficacy is most relevant when measured on the surface it is meant to protect, namely on human skin in vivo. Application of any material to the surface of the skin alters its optical properties. Diffuse reflectance spectroscopy (DRS) is a non-invasive technique to measure changes in the optical properties of the skin decoupled from its biological responses following sunscreen application. METHODS: This study compared measurements of UVA efficacy of oxybenzone and avobenzone at different concentrations (0-5%) using DRS, human phototest and an in vitro technique. Twenty subjects were enrolled for each product measured by DRS and 10 different subjects were enrolled for each product measured by human phototest. Six areas 5 cm x 10 cm were outlined on each subject's back. DRS measurements were performed on four subsites within each area before and 20 min after sunscreen application. UVA efficacy for each concentration of product was calculated from the measured transmission spectrum of a given product convoluted with the spectrum of a Xenon light source adequately filtered to obtain the UVA spectrum from 320 to 400 nm and the erythema action spectrum. Phototesting was performed using the same light source and persistent pigment darkening as the biological endpoint. Measurements were made with sunscreen coverage of 2 mg/cm2. In vitro measurements were performed using an Optometrics instrument. RESULTS: All three techniques showed a linear response between calculated UVA efficacy and product concentration. CONCLUSIONS: This study showed that DRS is a rapid and reproducible method to calculate UVA efficacy of sunscreen materials and that its results correlate closely with those obtained by human phototesting.

Diurnal and seasonal variations of the UV cut-off wavelength and most erythemally effective wavelength of solar spectra.

BACKGROUND: Biologically effective solar ultraviolet radiation is defined as the product of the intensity of the solar spectrum and the erythema action spectrum at each wavelength. In this way we may arrive at the weighted effectiveness of each wavelength of solar radiation to produce a sunburn reaction. There have been many measurements of the variation of the solar spectrum with the time of the day and the time of the year, but questions remain as to the variation of the quality of the spectrum and the contribution of the shortest wavelengths of solar terrestrial radiation. The purpose of the present study was to determine the variation of the biologically effective solar spectrum with the time of the day and the time of the year and to determine the variation of the shortest wavelength that contributes to the sunburn reaction with the time of the day and the time of the year. METHODS: Spectroradiometric measurements were made at ground level over the period of one year (1988-1989) and at different times of the day at latitude 29.5 degrees north. The measured spectral irradiance was multiplied wavelength by wavelength by the erythema action spectra. RESULTS: We determined that the biologically effective solar spectrum remains essentially the same over the times of the day that sunburn may be experienced. The maximally effective wavelength of biologically effective solar radiation was determined to be 308 nm. The cut-off wavelength for biologically effective solar radiation (defined as the wavelength at which the biologically effective solar radiation is at 1% of its maximum) varied from 291 to 295 nm over the time of the year and from 292 to 296 nm over the day. CONCLUSION: For all practical purposes the biologically effective spectrum of solar ultraviolet radiation may be considered to remain constant over the period when sunburn may occur and the minimal wavelength of sunlight that contributes to sunburn is in the range of 291-296 nm.

Suppression of UVB-induced cutaneous erythema by a previous UVB exposure.

People who vacation in sunny places are exposed to the sun on multiple occasions at least on a daily basis. The clinical assessment of sun exposure is erythema in the first 48 h after exposure and pigmentation at times greater than 3-5 days. The purpose of this investigations was to determine the extent to which consecutive erythemogenic exposures result in additive erythema responses. Studies were conducted in which volunteers were first exposed to a graded series of fluences of UVB radiation and then on subsequent days (1-3 days) the same sites along with the surrounding unexposed skin were challenged with varying fluences of UVB radiation. The erythema reactions were assessed clinically and were objectively documented with diffuse reflectance spectroscopy. The sites that received two exposures always showed a reduced erythema response compared to a single erythemogenic exposure. The suppression of erythema was more pronounced when the second exposure was given 48 h after the first. The erythema suppression was maximal when the first exposure was at 1.3 minimum erythema dose (MED). The pigment response to the first exposure was completely suppressed for fluences less than 1.5 MED. We thus provide evidence for a decoupling of the classical sequence of erythema-pigmentation response. We also show that the erythema induced by a second exposure may be substantially suppressed by an earlier exposure, and that this cannot be due to melanin photoprotection or due to substantial thickening of the stratum corneum. We propose that the cause may be some diffusible element of yet unknown origin.

Permeabilization and recovery of the stratum corneum in vivo: the synergy of photomechanical waves and sodium lauryl sulfate.

BACKGROUND AND OBJECTIVE: Photomechanical waves render the stratum corneum permeable and allow macromolecules to diffuse into the epidermis and dermis. The aim of this study was to investigate the combined action of photomechanical waves and sodium lauryl sulfate, an anionic surfactant, for transdermal delivery. STUDY DESIGN/MATERIALS AND METHODS: A single photomechanical wave was applied to the skin of rats in the presence of sodium lauryl sulfate. The sodium lauryl sulfate solution was removed and aqueous solutions of rhodamine-B dextran (40 kDa molecular weight) were applied to the skin at time points 2, 30, and 60 minutes post-exposure. The presence of rhodamine-B dextran in the skin was measured by fluorescence emission spectroscopy in vivo and fluorescence microscopy of frozen biopsies. RESULTS: The use of sodium lauryl sulfate delayed the recovery of the stratum corneum barrier and extended the time available for the diffusion of dextran through it. CONCLUSION: The combination of photomechanical waves and surfactants can enhance transdermal drug delivery.

Fluorescence excitation spectroscopy for the measurement of epidermal proliferation.

Fluorescence excitation spectroscopy was used to assess cellular turnover in human skin by monitoring changes of endogenous fluorescence. Epidermal proliferation was induced with alpha-hydroxy acids. Commercially available glycolic acid creams (8 and 4% wt/wt concentration) and a vehicle cream (placebo) were applied in a randomized double blinded fashion on subjects' forearms, twice daily for 21 days. Excitation spectra were recorded (excitation 250-360 nm, emission 380 nm) at days 0, 1, 3, 7, 10, 11, 14, 17 and 21. The 295 nm excitation band (assigned to tryptophan moieties) was used in this study as a marker for cellular proliferation. To further reduce the day-to-day variability of the skin fluorescence the intensity of the 295 nm band was normalized to the 334 nm band (assigned to collagen crosslinks). The fluorescence emission intensity from placebo-treated skin remained practically unchanged over the period of the measurements while the fluorescence intensity measured from the glycolic acid-treated skin increased monotonically with treatment. The rate of increase of the excitation intensity with treatment was found to be dose dependent. The epidermal 295 nm band may be used as a quantitative marker to monitor the rate of proliferation of epidermal keratinocytes noninvasively.

Aging and effects of ultraviolet A exposure may be quantified by fluorescence excitation spectroscopy in vivo.

The fluorescence properties of skin chromophores such as tryptophan and collagen cross-links might be useful markers of aging and photoaging. As the fluorescence of pepsin-digestible collagen cross-links was found to increase with aging and decrease with photoaging we investigated the characteristics of this dependence. In vivo fluorescence excitation spectra (emission at 380 nm) of SKH hairless mouse model skin are characterized by two bands centered near 295 nm and 335 nm due, respectively, to epidermal tryptophan moieties and pepsin-digestible collagen cross-links. Several groups of hairless mice were followed over a period of 18 mo to document changes in skin fluorescence with aging. Other groups of animals were exposed to either broad band or narrowband ultraviolet A radiation to determine the effects of ultraviolet A exposure on the fluorescence of the dermal collagen cross-links and to determine an action spectrum for the induced changes. We also found that the intensity of pepsin-digestible collagen cross-links in vivo increases linearly with age and that the fluorescence of epidermal tryptophan decreases linearly with age. We found that the fluorescence of pepsin-digestible collagen cross-links decreases immediately following exposure to ultraviolet A whereas epidermal tryptophan fluorescence increases. Both changes were dose dependent but the increase in tryptophan fluorescence occurred exclusively in young animals (2--6 mo old). We found that the ultraviolet-induced fluorescence decrease of pepsin-digestible collagen cross-links is wavelength specific. The action spectrum for the ultraviolet A effect on the in vivo fluorescence of pepsin-digestible collagen cross-links shows a distinct maximum at 335 nm that corresponds to the maximum in the fluorescence excitation spectrum due to pepsin-digestible collagen cross-links. Our results seem to indicate that in vivo fluorescence of epidermal tryptophan moieties and collagen cross-links in the dermal matrix may serve as markers for skin aging, for photoaging, and for immediate assessment of exposure to ultraviolet A radiation.

Photomechanical transdermal delivery: the effect of laser confinement.

BACKGROUND AND OBJECTIVE: Photomechanical waves can transiently permeabilize the stratum corneum and facilitate the delivery of drugs into the epidermis and dermis. The present study was undertaken to assess the effect of pulse characteristics to the penetration depth of macromolecules delivered into the skin. STUDY DESIGN/MATERIALS AND METHODS: Photomechanical waves were generated by confined ablation with a Q-switched ruby laser. Fluorescence microscopy of frozen biopsies was used to assay the delivery of macromolecules through the stratum corneum and determine the depth of penetration. RESULTS: Photomechanical waves generated by confined ablation of the target have a longer rise time and duration than those generated by direct ablation. Confined ablation required a lower radiant exposure (from approximately 7 J/cm(2) to approximately 5 J/cm(2)) for an increase in the depth of delivery (from approximately 50 microm to approximately 400 microm). CONCLUSIONS: Control of the characteristics of the photomechanical waves is important for transdermal delivery as they can affect the depth of drug penetration into the dermis.

In vivo fluorescence spectroscopy of nonmelanoma skin cancer.

In vivo and ex vivo tissue autofluorescence (endogenous fluorescence) have been employed to investigate the presence of markers that could be used to detect tissue abnormalities and/or malignancies. We present a study of the autofluorescence of normal skin and tumor in vivo, conducted on 18 patients diagnosed with nonmelanoma skin cancers (NMSC). We observed that both in basal cell carcinomas (BCC) and squamous cell carcinomas (SCC) the endogenous fluorescence due to tryptophan residues was more intense in tumor than in normal tissue, probably due to epidermal thickening and/or hyperproliferation. Conversely, the fluorescence intensity associated with dermal collagen crosslinks was generally lower in tumors than in the surrounding normal tissue, probably because of degradation or erosion of the connective tissue due to enzymes released by the tumor. The decrease of collagen fluorescence in the connective tissue adjacent to the tumor loci was validated by fluorescence imaging on fresh-frozen tissue sections obtained from 33 NMSC excised specimens. Our results suggest that endogenous fluorescence of NMSC, excited in the UV region of the spectrum, has characteristic features that are different from normal tissue and may be exploited for noninvasive diagnostics and for the detection of tumor margins.