An innovative method to measure skin pigmentation

Background/purpose: It is crucial to establish an accurate method for measuring skin pigmentation in cosmetic science and clinical dermatology. Here, we report a non-invasive precise method for measuring skin melanin content.
Methods: In order to determine the concentrations of melanin and hemoglobin in skin, we used the spectrum resolution (SR) method. In brief, the absorption spectrum of the skin was calculated from the reflection spectrum using a spectrophotometer. The concentrations of melanin and hemoglobin were then determined using a multiple regression analysis, assuming that the absorption spectrum of the skin is expressed as a linear summation of the absorptions of melanin and hemoglobin according to the Lambert–Beer law. The skin changes in the volar forearm, which had been irradiated by ultraviolet rays (UV), were observed daily by the SR method.
Results: A multiple regression analysis with an absorption spectrum of 500–700 nm was performed. The multiple correlation coefficient was 0.993, resulting in a satisfactory precise estimate of the concentrations of melanin. After UV irradiation, the concentration of melanin monitored by the SR method increased until 8 days and decreased gradually afterwards.
Conclusions: The SR method allows the evaluation of the changes of epidermal melanin induced by UV irradiation.     

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.     

In vivo evaluation of the protective capacity of sunscreen by monitoring urocanic acid isomer in the stratum corneum using Raman spectroscopy

Background/purpose: Urocanic acid (UCA) is a major ultraviolet (UV) ray‐absorbing component in the epidermis, and it isomerizes from the trans to the cis form upon exposure to UV radiation. Continuous measurement of UCA isomers in the skin at the same area is not available using conventional methods. This study aimed to evaluate the protective capacity of sunscreen by non‐invasively monitoring the trans‐UCA (t‐UCA) amount in the stratum corneum (SC) by confocal Raman spectroscopy. Methods: In vivo Raman spectra of the skin at the cheek or volar forearm were obtained from 27 healthy Japanese volunteers of different ages (age range, 22–53 years) throughout a whole year using confocal Raman spectroscopy. Eighteen healthy male Japanese volunteers (age range, 25–52 years) were enrolled for the evaluation of the protective capacity of sunscreen. The concentration depth profile of t‐UCA relative to keratin was calculated from the Raman spectra in the 400–2200 cm⁻¹ region. Then, the integrated amount within the depth of 0–12 μm was calculated, which represented the total amount of t‐UCA in the SC. Results: The integrated amount of t‐UCA in the cheek skin was significantly lower than that in the volar forearm skin throughout a year. The amount of it in the volar forearm skin was significantly the lowest in summer, but not in the cheek skin. The amount of t‐UCA decreased immediately after UV exposure even below 1 minimal erythema dose, remained low for 1 week, and gradually increased up to the initial level about 2 weeks after UV exposure. The decrease in the t‐UCA amount was hindered by the application of sunscreen on the skin surface. There were no statistical differences in response to UV exposure between the erythema‐positive and erythema‐negative groups. Conclusions: The monitoring of the amount of t‐UCA in the SC by confocal Raman spectroscopy is a good method to assess the efficacy of sun protective substances.     

Effects of p-coumaric acid on erythema and pigmentation of human skin exposed to ultraviolet radiation

Background. It has been recently recognized that p‐coumaric acid (PCA) is a strong inhibitor of cellular melanogenesis. Aim. To evaluate the erythema‐suppressive and skin‐lightening effects of PCA after topical application to human skin. Methods. The control and PCA cream products were applied twice daily to the skin of the forearm of 21 subjects before and after ultraviolet (UV) irradiation to determine whether they could prevent erythema formation and pigmentation. The cream products were also applied to different areas only after the induction of erythema or pigmentation to determine whether they could have a depigmenting effect. Results. A 7‐day application of control and PCA cream products before UV irradiation decreased UV‐induced erythema formation by 31% and 77%, respectively, compared with untreated skin. When the PCA cream was applied after UV irradiation, its effects on skin colour or pigmentation were less remarkable. However, the melanin index was significantly decreased at the sites treated with PCA cream for 70 days compared with control sites, and the Individual Typology Angle (ITA°) value was increased significantly. Of the 21 subjects, 2 had mild adverse skin reactions to both the PCA and control creams. Conclusion. These results suggest that PCA cream can reduce UV‐induced erythema formation and subsequent pigmentation in human skin.     

Sensitivity of mouse Skh:HR-2 to ultraviolet radiation: melanocyte inactivation

The hairless mouse, Skh:HR-2, was exposed to doses of ultraviolet (UV) radiation known to induce skin pigmentation. Three parameters associated with perturbations in skin pigmentation were monitored following UV exposure. These include spectroscopy (skin darkness), histology (melanocyte density), and biochemistry (melanin). Within 90 min of UV exposure, the skin became lighter. This was associated with a reduction of quantifiable melanin and the inactivation of epidermal melanocytes.     

Photosensitivity of murine skin greatly depends on the genetic background: clinically relevant dose as a new measure to replace minimal erythema dose in mouse studies

Artificial UV irradiation of murine skin is a frequently used method for testing photosensitivity, study carcinogenesis and photoprotective effects of different compounds. However, doses of UV radiation and mouse strains used in experiments vary greatly. The genetic background of mice may influence the photosensitivity as melanin content, pigmentation and hair cycle parameters are dissimilar. Doses of UV are often expressed in relation to the minimal erythema dose (MED) that was not necessarily determined for the given strain. We set out to standardize the method of measuring photosensitivity in three commonly used mouse strains, C57BL/6N, Balb/c and SKH‐1. We found that MED may not be determined for some strains as erythema development in mice with diverse genotypes differs greatly. We measured the oedema response in vivo and ex vivo by using OCT. Given the strain‐specific variability of erythema, we introduced Clinically Relevant Dose (CRD) as a new term to replace MED in experiments, to describe the lowest dose that triggers a perceptible skin reaction in mice. Not only the CRD but the proportion of erythema and oedema were different in strains examined. C57BL/6N mice display skin reactions at the lowest UVB dose, while SKH‐1 hairless mice show changes, mostly oedema, after higher doses of UVB. The cellular composition and skin thickness were examined by histopathology. IL‐1beta and IL‐6 levels in skin correlated with the increasing doses of UVB. Despite the variations in the degree of erythema and oedema, no major differences in cytokine expressions were seen among various strains of mice.     

内皮素拮抗剂对中波紫外线诱导豚鼠色素沉着的观察

目的 探讨内皮素拮抗剂对紫外线诱导豚鼠色素沉着的治疗作用.方法 用中波紫外线(UVB)照射豚鼠皮肤制作色素沉着模型.模型制作成功后,模型动物分为空白对照组(生理氯化钠溶液)、内皮素拮抗剂组及熊果苷组(阳性对照).分别于中波紫外线(UVB)照射前、15 d后及30 d后,用Mexameter(R) MX 18检测豚鼠背部皮肤的黑素指数.连续治疗30 d后比较黑素指数、表皮内黑素细胞数目和黑素含量等指标.结果 UVB照射30 d时,豚鼠背部9块UVB照射区域的黑素指数显著高于照射前(P＜ 0.000 1).外涂1‰内皮素拮抗剂的照射区域30 d后的黑素指数值明显降低,和熊果苷组比较,差异有统计学意义(P＜ 0.000 1).内皮素拮抗组黑素含量指数1明显低于空白对照组(P＜0.05).而3组间黑素含量指数2差异无统计学意义(P＞ 0.05).结论 外涂内皮素拮抗剂对UVB照射诱导豚鼠的色素沉着有一定治疗作用.     

The minimal melanogenesis dose/minimal erythema dose ratio declines with increasing skin pigmentation using solar simulator and narrowband ultraviolet B exposure

Purpose: To investigate the relation between pre‐exposure skin pigmentation and the minimal melanogenesis dose (MMD)/minimal erythema dose (MED) ratio after a single narrowband ultraviolet B (nUVB) and solar simulator (Solar) exposure. Background: In fair‐skinned individuals, it is well known that the UV dose to give pigmentation (MMD) after a single exposure to UVB is larger than the UV dose to elicit erythema (MED) (MED<MMD), but it remains to be established if this is true also in dark‐skinned individuals. Methods: Eighty‐four volunteers with a wide variation in skin pigmentation (Fitzpatrick skin types I–V) were included. Results: After a single Solar or nUVB exposure we found that the ratio MMD/MED depends on skin pigmentation. In light‐pigmented individuals, up to 1.9 MED is required to induce pigmentation (MMD). The MMD/MED ratio is about 1.5 in medium‐pigmented and dark‐pigmented individuals. In very brown‐pigmented individuals the MMD/MED ratio is 1 (MED=MMD). This connection was most pronounced for facultative skin at wintertime. The ratio was almost stable for constitutive pigmentation with MMD/MED=1.3. The ratios were almost independent of skin type. Conclusion: The ratio MMD/MED is highly dependent on skin pigmentation after a single exposure to Solar or nUVB and is independent of skin type.     

Facultative skin pigmentation in caucasians: an objective biological indicator of lifetime exposure to ultraviolet radiation?

To investigate age and gender trends in facultative and constitutive skin pigmentation we measured skin pigmentation non-invasively and objectively by skin reflectance spectroscopy in 653 caucasians (336 females and 317 males; mean age 38 years, range 0–85) who were not using artificial tanning devices. In all subjects, measurements were performed in the late winter and pre-spring period at five sites exposed to ultraviolet (UV) radiation: the forehead, the upper chest, the upper back and the lateral and medial aspects of the upper arm, and in UV-unexposed buttock skin. Constitutive pigmentation at the buttocks was highest in the first years of life and then decreased substantially during the first two decades of life ( P  < 0.01). After the age of 25 years, buttock pigmentation remained at a constant level ( P  = 0.20). There was no gender difference in constitutive pigmentation. Facultative skin pigmentation increased with age for all the measured sites with the highest levels found at the lateral aspect of the upper arm. Based on observations in this study we propose the idea of a 'sun exposure index' (SEI) for individuals, based on objective measurements of skin pigmentation. The SEI is calculated as the increase in facultative pigmentation above the constitutive level and is expressed as a percentage of the constitutive level. The SEI appeared to be related to cumulative lifetime UV exposure and may be used in epidemiological research as an objective estimate of UV exposure at different body sites in caucasians.     

Spectral responses of melanin to ultraviolet A irradiation

The purpose of this investigation was to study the ultraviolet A-induced effects on melanin pigmentation both in an in vitro model system and in vivo. Ultraviolet-Vis absorbance spectra of L-3,4-dihydroxyphenylalanine-melanin solutions at different concentrations were measured before and after ultraviolet A exposure (10-120 J per cm2). The difference spectra reveal that following ultraviolet A exposure the absorbance increases exponentially from 800 nm to 450 nm accompanied by a prominent decrease of absorbance in the ultraviolet A range. This change of spectral features depends on both ultraviolet A doses and melanin concentrations. The photo-bleaching effect observed in the ultraviolet A range also depends on oxygen. Human subjects were irradiated with ultraviolet A (40-80 J per cm2) on their back and diffuse reflectance spectra were collected at both irradiated and untreated sites. The absorption spectra of ultraviolet A-induced pigment were calculated as the difference of the two. The ultraviolet A-induced pigment in vivo has similar spectral characteristics and dose dependency as the in vitro system. Photo-oxidation of pheomelanin solutions presents distinctively different spectral and dose-response characteristics from eumelanin. After ultraviolet A irradiation pheomelanin absorbance decreases both in the visible and the ultraviolet A range. We conclude that irradiation with ultraviolet A induces significant photochemical alterations in the skin witnessed by increased photoprotection in the visible spectral range and reduced protection in the ultraviolet A range. We suggest that soluble melanin plays an important part in ultraviolet A-induced pigment in skin and two distinct absorption mechanisms of melanin may be involved in ultraviolet A photo-oxidation. We also propose that eumelanin and pheomelanin could be differentiated according to their spectral responses to ultraviolet A irradiation.     

Q‐switched ruby laser irradiation on spotty pigmentation in the skin of the hairless dog

OBJECTIVE: To investigate macroscopically and histopathologically the dermatological changes after Q‐switched ruby laser (QRL) irradiation with different exposure doses in UVB‐induced pigmentation in hairless dogs.

METHODS: QRL irradiation with 3.0, 5.0 and 7.0?J/cm² was carried out on the UVB‐induced spotty pigmentation in the skin of the hairless dog. Gross appearance was observed daily throughout this study. Histopathological examination was performed 1 day before QRL irradiation and 1 and 3 days and 1, 2, 3, 4, 5, 6, 7, 8, 10, 12, 14 and 16 weeks after QRL irradiation.

RESULTS: Immediately after QRL irradiation, spotty pigmentation was removed. One week after QRL irradiation, re‐epithelialization started from the margin of the irradiated sites. between 5 and 10 weeks after QRL irradiation, the skin color returned to normal and some portions showed recurrence of hyperpigmentation. Histopathologically, spotty pigmentation had a heavy deposition of melanin granules in the stratum basale, spinosum and corneum. One day after QRL irradiation, the skin showed destruction of melanin granules. Seven days after QRL irradiation, re‐epithelialization began from the surroundings of the QRL‐irradiated sites and the pilosebaceous units. The delayed process of re‐epithelialization was dependent on the incident exposure dose with QRL. The repaired epidermis was devoid of melanin granules. By 5 weeks after QRL irradiation with 3.0 and 5.0?J/cm², the stratum basale and spinosum revealed a redistribution of melanin granules. In the sites of recurrent hyperpigmentation, the bases of the remaining hair follicles showed a notable increase in the reproduction of melanin granules. Melanin granules abundantly aggregated in the bottom portion of the nucleus in each epidermal cell.

CONCLUSION: These results revealed that hairless dogs were invaluable laboratory animals, which developed spotty pigmentation after successive UVB irradiation. In addition, UVB‐induced spotty pigmentation in hairless dogs is useful for investigating the process of depigmentory treatment with QRL irradiation and recurrence of this lesion.     

Pigmentation in Koreans: study of the differences from caucasians in age, gender and seasonal variations

BACKGROUND: Human skin colour shows variations throughout life, and many extrinsic and intrinsic factors influence melanogenesis. Facultative pigmentation of sun-exposed skin has been suggested to reflect cumulative lifetime ultraviolet (UV) exposure in caucasians. However, pigmentary changes due to various regulatory factors may be different in dark-skinned peoples. OBJECTIVES: To observe the variations in skin colour due to ageing, gender differences and seasonal changes in Koreans with skin type IV or V. METHODS: Skin pigmentation was measured at five body sites (buttock, glabella, the V of the neck area, inner arm and dorsal forearm) using skin reflectance spectroscopy in 497 subjects (age range 0-87 years) in winter and 311 subjects (age range 0-84 years) in summer. Among these subjects, 110 were assessed in both seasons. Three independent measurements at each site were done and the average value was used as the pigmentation level. RESULTS: Constitutive pigmentation of the buttock was highest in the first decade of life. It then decreased during the second decade and this decreased level was maintained after the third decade. In contrast to caucasians, facultative pigmentation and sun exposure index did not increase with ageing. Gender differences were significant at all body sites after the first decade. Seasonal changes were apparent in dorsal forearm pigmentation. Little difference was seen in forehead pigmentation between summer and winter. CONCLUSIONS: Basal melanogenic regulation might not be different between Asians and caucasians. However, the sun exposure index may not represent lifelong cumulative UV exposure in Koreans. Age-, gender- and season-related characteristics of skin pigmentation in Koreans imply that genetically determined basal skin colour plays an important part in characterizing later responsiveness to UV radiation and sex hormones. Understanding differences between races will be helpful in studying the regulatory mechanisms of melanogenesis.     

Long-term evaluation of erythema and pigmentation induced by ultraviolet radiations of different wavelengths

BACKGROUNDS/AIMS: Although multiple studies have been reported about the biological effects of ultraviolet (UV) radiations, the comparative and long-term reactions of human skin by several different UV-wavebands were not reported. The aim of this study was to investigate a time course of erythema and pigmentation induced by UVA 1, broad-band UVA (BBUVA), narrow-band UVB (NBUVB) and broad-band UVB (BBUVB). METHODS: Ten volunteers participated in this study for 6 months. Four skin areas, from the back of each subject, were irradiated with two minimal erythema dose (MED) of four different UV wavelengths corresponding to UVA 1, BBUVA, NBUVB and BBUVB. Skin color changes were evaluated by visual scoring and values were converted into the L*a*b color system. RESULTS: For both UVA 1 and BBUVA, erythema and pigmentation were most pronounced immediately and 1 h after exposure. Thereafter, erythema rapidly diminished but pigmentation persisted throughout the study. For both NBUVB and BBUVB, test areas reacted with erythema of maximum intensity at 1 and 2 days, respectively. A maximum tanning was reached at 3-6 days for NBUVB and 4-7 days for BBUVB, and the return toward the original color point was at 1 and 3 months, respectively. No significant difference was found in visual and colorimetric evaluation for the time course of skin color changes. CONCLUSION: Two MED of UVA produced far prolonged erythema and pigmentation than UVB. For UVA, UVA 1 and BBUVA showed similar intensity and time course of skin reaction. For UVB, erythema and pigmentation produced by NBUVB were milder in intensity and shorter in time course than those by BBUVB. These results would provide standard data on time courses and intensity of skin color changes by different UV wavelengths.     

Epidermal photoprotection: comparative study of narrowband ultraviolet B minimal erythema doses with and without stratum corneum stripping in normal and vitiligo skin

Background. Recent accumulating data in the literature have indicated a complex photoprotective role of the epidermis, and the role of melanin as the major epidermal photoprotective mechanism has become debatable. Aim. Comparative assessment of the photoprotective roles played by different epidermal structures and compounds. Methods. In total, 64 participants, comprising patients with vitiligo (n = 32) and healthy volunteers (n = 32), with skin phototypes (SPTs) II to V, were enrolled in the study. Areas of skin were delineated; for both lesional and nonlesional skin, the stratum corneum (the SC) was stripped, followed 24 h later by exposure to narrowband ultraviolet B (NB‐UVB) irradiation, to measure the minimal erythema dose (MED) in normal, stripped normal, vitiliginous and stripped vitiliginous skin models. These MED values were used to assess the photoprotective role of epidermal structures: melanin, viable epidermis (VE) and the SC. Results. In the vitiligo group, the MED values were significantly (P < 0.05) different between the skin models, being highest in normal skin, followed by stripped normal, vitiliginous and stripped vitiliginous skin. A similar significance level was found within each SPT for almost all comparisons. There was also a significant (P < 0.001) positive correlation between MED and SPTs. There were also significant (P < 0.05) differences in MED values calculated for epidermal structures, being highest for VE, followed by melanin and then the SC, and there was a significant (P < 0.05) positive correlation between MED and SPTs. Conclusion. Epidermal photoprotection may extend beyond melanin production, involving several factors such as epidermal layer thickness, optical properties and chromophores. Such a role was perceived to be reactive to UV irradiation, and more efficient in those with higher SPTs.     

A long-term evaluation of erythema and pigmentation induced by ultraviolet radiations of different wavelengths

BACKGROUND/AIMS: The long-term reactions of human skin by different ultraviolet (UV)-wavebands were not reported. This study was to investigate a time course of erythema and pigmentation induced by UVA-1, broadband UVA (BBUVA), narrowband UVB (NBUVB) and broadband UVB (BBUVB). METHODS: Ten volunteers participated in this study for 6 months. Four skin areas, from the back of each subject, were irradiated with two minimal erythema dose (MED) of four different UV wavelengths corresponding to UVA-1, BBUVA, NBUVB and BBUVB. RESULTS: For both UVA-1 and BBUVA, erythema and pigmentation were most pronounced immediately and 1 h after exposure. Erythema rapidly diminished but pigmentation persisted throughout the study. For both NBUVB and BBUVB, test areas reacted with erythema of maximum intensity at 1 and 2 days, respectively. A maximum tanning was reached at 3-6 days for NBUVB and 4-7 days for BBUVB, and the return toward the original point was at 1 and 3 months, respectively. CONCLUSION: Two MED of UVA produced far prolonged erythema and pigmentation than UVB. For UVA, UVA-1 and BBUVA showed similar intensity and time course of skin reaction. For UVB, erythema and pigmentation produced by NBUVB were milder in intensity and shorter in a time course than those by BBUVB.     

Spectroscopic assessment of dermal melanin using blue vitiligo as an in vivo model

BACKGROUND: Spectroscopic methods have been used to analyze in vivo melanin in the past but the specific effect of melanin depth on autofluorescence and reflectance spectroscopy has not been determined. In patients with blue vitiligo, three distinctive clinicopathologic patterns are present: (1) normal skin with normal epidermal melanin pigmentation (2), skin of blue vitiligo with dermal melanin pigmentation, and (3) tissue of regular vitiligo with no melanin pigmentation. Blue vitiligo may thus serve as an in vivo model to assess dermal pigment using spectroscopic techniques. OBJECTIVES: To evaluate the reflectance and autofluorescence spectra of a patient with blue vitiligo in order to assess the effect of melanin pigmentation and its localization on the optical properties of the skin. METHODS: The blue-gray, normal and depigmented lesions of a patient with blue vitiligo were analyzed using reflectance and fluorescent spectroscopy. The condition was likely induced by a phototoxic reaction in a patient with pre-existing vitiligo. These data were then correlated to the histologic and electron microscopic findings present in the various types of lesions. RESULTS: Reflectance spectroscopy detected little difference in spectral shape between skin sites affected by blue vitiligo vs. vitiligo. Autofluorescence spectroscopy detected an apparent difference between the two types of lesions, with the blue-gray lesions (blue vitiligo) showing lower fluorescence intensity and spectral maximum position red-shifted compared with regular vitiligo, whereas regular vitiligo showed more intense hemoglobin absorption than the blue vitiligo. CONCLUSIONS: Dermal melanin present in blue vitiligo can be well characterized by autofluorescence spectroscopy, while little difference in reflectance spectral shape exists between vitiligo and blue vitiligo. Thus, autofluorescence spectroscopy may better identify deeper structures in skin tissue, such as melanin, than reflectance spectroscopy.     

Cutaneous solar ultraviolet exposure and clinical aspects of photodamage

Solar ultraviolet (UV) radiation reaching the earth is a combination of UVB (290-320 nm) and UVA (320-400 nm) wavelengths. Since UVA is less energetic than UVB, UVB has long been thought to be the factor responsible for the damaging effects of solar radiation. But with modern tools such as in vitro models, it has been proven that UVA plays a major role. The objective of this review is to show how skin may be exposed to UV light and to highlight the clinical aspects of UV-induced skin damages with the respective contribution of UVB or UVA. Even if UVA is less energetic than UVB, it is more abundant and penetrates deeper into the skin, reaching as far as the dermis. Various factors also influence skin exposure to UV light: the latitude, season, and time of the day. Acute as well as chronic sun exposure induces short- and long-term clinical damages. Erythema and pigmentation are immediate responses of normal human skin exposed to UV radiation. The long-term effects are photoaging and photocarcinogenesis. In particular, UVA appears to play a major role in the deterioration of dermal structure leading to the photoaged appearance of the skin.     

Prediction of minimal erythema dose with a reflectance melanin meter

The relationship between skin pigmentation and sensitivity to ultraviolet (UV) radiation-induced erythema was investigated in 60 healthy subjects of sun-reactive skin types I-V. Using a portable reflectance spectrometer, skin pigmentation was measured as the melanin index (MI) in all subjects. A solar-simulated array of filtered UVA and UVB-emitting fluorescent lamps was then used to determine the UVB minimal erythema dose (MED) of each subject. MI readings and MED testing were both performed on the subjects mid to upper backs. Using this technique, we found a close correlation between MI and MED. Comparison of the mean MI or MED of subjects with different skin types revealed progressive differences in MI and MED between all five skin types. Erythema doseresponse curves, which provide further information about UV sensitivity, were also calculated for 43 subjects. A significant negative correlation was found between the gradients of these curves and both MI and MED. indicating that paler subjects respond more strongly to increments of UV above the MED than subjects with greater pigmentation. Our results indicate that although traditional, subjective means of predicting UV sensitivity to erythema are not without some value. MED correlates particularly strongly with objective measures of skin pigmentation. We therefore conclude that the reflectance spectrometer can rapidly and accurately predict UVB sensitivity, and should prove clinically useful for planning and optimizing UVB phototherapy.     

Dynamics of pigmentation induction by repeated ultraviolet exposures: dose, dose interval and ultraviolet spectrum dependence

Background The dynamics of ultraviolet (UV)‐induced melanogenesis have been well characterized for single UV exposures. However, our knowledge of the effects of repeated UV exposures on the development of new pigmentation is limited. Objectives To characterize the dynamics and dose dependence of pigmentation induction by repeated UV exposures using two different UV sources. Methods A total of 40 healthy subjects participated in the study: 21 were exposed to a 5% UVB/95% UVA source and 19 were exposed to a 2% UVB/98% UVA source. Skin phototypes 2–3 were represented. Subjects were exposed one to three times per week. The minimal erythemal dose and minimal melanogenic dose of all subjects were determined, and both visual and instrumental observations of the development of pigmentation and erythema were recorded. Results Dark‐brown pigmentation could be produced by a cumulative UV dose of 4200 J m^?2 given as 10 exposures over 5 weeks. However, comparable pigmentation could also be induced by a cumulative dose of 2900 J m^?2 given as eight exposures over 4 weeks. The lowest cumulative dose of 1900 J m^?2 given over 4 weeks produced moderate pigmentation. The 2% UVB source led to earlier and darker pigmentation than the 5% UVB source did for equally erythemogenic doses. Conclusions These observations show that the dynamics of melanogenesis induced by repeated exposures depends on UV dose, dose interval and emission spectrum. They also indicate that increasing the UV dose above a certain level of cumulative exposure does not significantly increase the level of UV‐induced pigmentation.