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.     

Assessment of the usefulness of skin phototype and skin color as the parameter of cutaneous narrow band UVB sensitivity in psoriasis patients

BACKGROUND: Many reports have been released to assess skin types, skin colors and cutaneous sensitivity to broad band UVB or UVA. OBJECTIVE: This study was performed to investigate the usefulness of skin type and skin color as the parameter of narrow band UVB (NBUVB) sensitivity. METHODS: The minimal erythema dose (MED) of 40 psoriasis patients was investigated by irradiating several doses ranging from 200 to 1500 mJ/cm2. Before phototesting, the skin color of buttock was measured with a tristimulus colorimeter. RESULTS: The median and mode value of MED of NBUVB was 950 mJ/cm2. Skin type was well correlated with the MED and there was a significant relationship between the L* value and MED, but not for the a* and b* values. CONCLUSION: The MED value of NBUVB in our study is a basic data to set the phototherapy protocol. Our result showed that skin type and L* value might be useful for predicting the sensitivity to NBUVB irradiation.     

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.     

The Relationship among Minimal Erythema Dose,Minimal Delayed Tanning Dose,and Skin Color

The relationship among minimal erythema dose (MED), minimal delayed tanning dose (MDTD), and skin color was examined in 16 healthy volunteers using three different spectra. The subjects were exposed to UVB, UVA+B, and UV+Visible light (UV+Visible) with a xenon arc solar simulator as a light source. The MEDs for UVB and UVA+B were less than the MDTDs, whereas the MED for UV+Visible was higher than the MDTD. There was no significant correlation between the MED and the MDTD for UVB or UVA+B. The MED for UV+Visible was significantly correlated to the MDTD (p<0.01). Skin color significantly correlated with MEDs for UVB and UVA+B (p<0.01), but not for UV+Visible. There was no significant correlation between skin color and the MDTD for any spectra. From these results, it is suggested that the relationship between erythemal and melanogenic responses is dependent on spectral bands of the light source and that skin color is a predictor of UV-induced erythema.     

Age dependence of ultraviolet light-induced erythema following narrow-band UVB exposure

BACKGROUND/PURPOSE: A report in the literature suggests longer duration and greater intensity of late phase UVB erythema in older people. The aim of this study was to identify differences in minimum erythema dose (MED) and intensity of UV-induced erythema after narrow band UVB exposure between older and younger individuals in the late phase of UVB erythema. METHODS: Using the UVA/TL 01 UV skin tester (Waldmann Medizintechnik, Villingen-Schwenningen, Germany), MED was determined for narrow-band UVB exposure in 20 young subjects aging from 20-40, and 20 elderly subjects over 70 years of age. The intensity of UV-induced erythema was measured by chromametry (a*-value and L-value) and laser Doppler 48 h after irradiation. Minimum erythema dose (MED) was additionally assessed visually. RESULTS: Elderly subjects showed no statistical different MED compared to younger subjects. However, the erythema intensity 48 h after narrow-band UVB exposure was significantly greater in the elderly. CONCLUSIONS: Narrow-band UVB therapy may, in case of over dosage, produce more intense erythema in the late phase of UVB erythema in old people than in younger individuals.     

The relationship of skin color, UVB-induced erythema, and melanogenesis

The relationship between skin color, delayed erythema, and delayed tanning (DT) elicited by a single exposure of UVB was investigated. Both constitutive and facultative pigmentation were determined by skin reflectance using a melanometer. Skin reflectance using visible light was well correlated to the minimal immediate pigment darkening dose elicited by UVA irradiation, which may relate to epidermal melanin content, a determinant of skin color. Minimal erythemal dose (MED) was well correlated to skin color, but there was less correlation between minimal melanogenic dose and skin color or the MED, since melanogenesis is controlled by genetic factors. DT also correlated to the dose of UVB in terms of MED. A coefficient of the regression line of DT may suggest the tanning capacity of skin. The possibility of detecting mild photosensitivity in individuals from a regression line of the MED on skin color is suggested.     

Dosimetry of solar ultraviolet radiation. Daily and monthly changes in Paris

The intensity of ultraviolet A and B radiations was measured in Paris (48 degrees North) by means of silicon photoelectric cells (Osram Centra dosimeter) from December, 1984 till February, 1986. The results, which must be regarded as approximate, are expressed as physical units (mW/cm2) and biological units (minimal erythema dose/hour). For sunny days two curves are presented separately for UVB and UVA: daily variations in radiation (hourly measurements) and daily variations at 11 hours (solar time) during one year. Maximum irradiation was observed at noon in early July: UVB 0.15 mW/cm2, UVA 5.4 mW/cm2. Between December and July the amount of UVB radiation was multiplied by 14 and that of UVA radiation by 9. For subjects with clear photo-type and when the sun was at its zenith, an MED per hour was obtained from May 1 onwards. Within a day, 30 p. 100 (summer) and 50 p. 100 (winter) of erythema-producing UV intensity were delivered between 11 and 13 hours (solar time). This kind of study has numerous clinical applications: advice regarding exposure to sun rays, dosing of heliotherapy, epidemiological data concerning photodermatitis (circumstances of exposure, UV threshold dose) and photocarcinogenesis (determination of annual MED doses in relation to areas of uncovered skin and occupational exposure to sun rays). Other studies on the French territory will provide a map of UV irradiation.     

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

Ultraviolet (UV) radiations from sunlight that reach the surface of the earth are categorized as UVB (wavelength range 280–320 nm) and UVA (320–400 nm). The UVA is further divided into UVA2 (320–340 nm) and UVA1 (340–400 nm). In the United States and other nations, rules have been set outlining how products that are designed to protect against UVB and UVA should be tested, and there are also strict rules about how these products can be labeled. The SPF (sun protection factor) mainly shows the level of protection against UVB only, and SPF along with “Broad Spectrum” on a label shows protection against both UVB and UVA. The criteria that decide whether or not manufacturers can claim a product gives broad spectrum protection, in the US, primarily focus on protection offered below 370 nm. Visible light (VL), which ranges from 400 nm to 700 nm, is a spectrum of wavelengths that are visible to the human eye. To date, only the UV part of sunlight, which is not visible light, has been considered to cause photodamage (damage caused by sunlight) resulting in skin cancers and photoaging (skin ageing due to the sun). The visible part of the sunlight was considered relatively harmless. This study, from the US, investigated skin responses, in terms of sunburn and tanning, caused by visible light in combination with the tail end of long wavelength UVA1 (referred to as VL+UVA1, 370–700 nm) and compared them to those caused by pure visible light (400–700 nm). The findings of the study show that skin responses, in terms of pigmentation (colouring/tanning) and erythema (redness/sunburn), resulting from VL+UVA1 were stronger than those induced by pure visible light alone. This implies that wavelengths that current broad spectrum sunscreens do not cover can affect pigmentation and erythema. These wavelengths may have a role in conditions aggravated by sun exposure such as melasma and post‐inflammatory hyperpigmentation, especially in patients with skin of color. The development of prodcts that protect against visible light and long wavelength UVA1 will be helpful for these, as well as for the management of certain skin disorders triggered by UVA1 and VL.     

The relation between constitutional skin color and photosensitivity estimated from UV-induced erythema and pigmentation dose-response curves

In 54 healthy volunteers we assessed predictors of sensitivity to ultraviolet (UV) light, including Fitzpatrick's sun reactive skin types and constitutional skin color, and compared these with one another and with responses of the skin to UV irradiation, as determined experimentally by a minimal erythema dose (MED), a minimal melanogenic dose (MMD), and dose-response curves for UV-induced erythema and pigmentation. For these studies, a xenon arc solar simulator was used as the source of UV irradiation, and a chromameter interfaced with a computer for objective measurement of UV-induced erythema and pigmentation was employed. The skin type did not correspond well to the constitutional skin color, as measured by a chromameter prior to UV irradiation. Within each skin type, there were large ranges of MED and MMD values and great variability in the shapes of the dose-response curves. Constitutional skin color was also not a good predictor of the measured MED and MMD values but did appear to correlate with the steepness of the dose-response curves for erythema and for pigmentation. From these studies, we propose that objectively measured constitutional skin color is a better predictor of UV responses of the skin than skin type and that steepness of dose-response curves for erythema is a better measure of the response of the skin to UV irradiation than is a MED measurement.     

广州地区102例正常人紫外线最小红斑量测定

目的:测定广州地区正常人紫外线最小红斑量(MED)的正常值范围,探讨其与性别、年龄、皮肤日光类型的关系。方法:以SUV1000型日光紫外模拟器作为照射光源,测定102名健康志愿者腹部正常皮肤的MED值(Ⅲ型、Ⅳ型皮肤)。结果:102名受试者MED均值:UVA为50.0 J/cm2,UVB为43.0 m J/cm2。不同皮肤类型间,Ⅲ型皮肤MED均值:UVA为38.5 J/cm2,UVB为36.1 m J/cm2;Ⅳ型皮肤MED均值:UVA为50.0 J/cm2,UVB为47.0 m J/cm2,Ⅳ皮肤MED均值均明显大于Ⅲ型皮肤(P值均<0.01)。不同性别间,男性MED均值:UVA为50.0 J/cm2,UVB为43.0 m J/cm2;女性:UVA为50.0 J/cm2,UVB为43.0 m J/cm2,不同性别间差异均无统计学意义(P值均>0.05)。不同性别的不同年龄阶段间UVA、UVB MED均值差异均无统计学意义(P值均>0.05);UVA-MED的正常值范围为≥30 J/cm2,UVBMED的正常值范围为≥29.1 m J/cm2。结论:紫外线MED的影响因素与皮肤日光反应类型有关,Ⅲ型皮肤UVA-MED、UVB-MED均明显低于Ⅳ型皮肤(P<0.01)。本组受试者MED与性别和年龄无直接关系。     

Failure of physiologic doses of pure UVA or UVB to induce lesions in photosensitive cutaneous lupus erythematosus: implications for phototesting

BACKGROUND: Phototesting studies in cutaneous lupus erythematosus have yielded variable results, with most trials reporting photo-induction of lesions by both UVA and UVB in substantial numbers of patients. OBJECTIVES: To determine the minimal erythema dose in patients with subacute cutaneous lupus erythematosus (SCLE) and controls. PATIENTS/METHODS: We phototested nine patients with SCLE and 14 skin type-matched controls, using repetitive dosing of UVA1 and UVB, but with filters that removed most of the shorter UVC and longer infrared and visible light. In addition, DNA was isolated from anticoagulated blood to genotype the TNF-alpha 308 region in each patient and control. RESULTS: We were unable to demonstrate a difference in minimal erythema dose (MED) between patients and controls, or any correlation of MED with either TNF genotype or systemic drug therapy for SCLE. In addition, no SCLE skin lesions were induced in the nine patients with either UVA or UVB, and one patient cleared a skin lesion after low-dose UVA1 irradiation. CONCLUSIONS: The potential role of wavelengths outside the UVA and UVB range in the photo-induction of cutaneous lupus skin lesions needs to be investigated, and there is a need to standardize phototesting equipment and procedures for patients with cutaneous lupus erythematous.     

Lack of photoprotection against UVB-induced erythema by immediate pigmentation induced by 382 nm radiation

Immediate pigment darkening (IPD) was induced on the backs of 11 human volunteers of skin types III and IV by exposing the skin to UVA radiation (382 nm). The minimum erythema dose (MED) of UVB radiation was also determined by exposing sites to graduated doses of 304 nm radiation. The order of exposure of distinct anatomic areas was as follow: UVB followed by IPD induction; IPD induction followed by UVB; IPD induction followed 3 h later by UVB; and UVB only. Erythema responses induced by UVB were graded by inspection 24 h later and the MEDs in the 4 areas were compared. The induction of IPD before UVB exposure caused no significant change in the MED compared to sites receiving UVB only, or receiving UVA radiation after UVB, confirming that the IPD reaction does not protect against UVB-induced erythema. There was also no evidence of photorecovery, i.e., an increase in the MED of UVB resulting from exposure to longer wavelength, UV or visible radiation following UVB exposure.     

118例志愿者紫外线最小红斑量值测定

目的 测定118例志愿者长波紫外线(UVA)和中波紫外线(UVB)的最小红斑量(MED)正常值。方法 以SUV1000型日光紫外模拟仪为光源,测定118例健康志愿者和非炎症性皮肤病患者UVA-MED和UVB-MED正常值。结果 UVA-MED均值男性为55J/cm²(18-95J/cm²),女性40J/cm²(15-100J/cm²);UVB-MED均值男性31mJ/cm²(12-95mJ/cm²),女性29mJ/cm²(8-95mJ/cm²)。男性UVA-MED显著高于女性(P<0.05),UVB-MED两性间差异无统计学意义(P>0.05)。皮肤光反应类型为Ⅲ型的受试者UVA-MED和UVB-MED均显著低于Ⅳ型(两种类型皮肤UVA-MED:在男性、女性均P<0.05;UVB-MED:在男性P<0.05,女性P<0.01)。女性的年龄与MED值无关;30-49岁男性UVB-MED低于其他年龄组,UVA-MED与年龄无关。遮光部位测得的UVA-MED和UVB-MED与户外停留时间长短无关。结论 皮肤光反应类型是决定MED的重要因素。     

Quantitative assessment of UV-induced changes in microcirculatory flow by laser Doppler velocimetry

Objective measurements of blood flow changes following UV irradiation in the skin of human volunteers have been made with the noninvasive technique of laser Doppler velocimetry (LDV). This optical procedure allowed perfusion (number of red cells X velocity) alterations in the cutaneous microcirculation to be monitored after exposure of the skin to UVA and UVB + UVC radiation. Response curves were obtained in 6 subjects following irradiation at 4 times the minimal UVB + UVC erythema dose (MED). Measurements were made on control (untreated) skin and on skin pretreated with a sunscreen lotion. It was found that: (1) the lotion vehicle had no protective effect, (2) the active sunscreen constituent (2-ethylhexylcinnamate, 5%) was significantly protective, and (3) the presence of bergapten (5-methoxypsoralen, 30 ppm) did not enhance or diminish the cinnamate protective effect. LDV measurements in 5 subjects were also taken during and subsequent to 5 daily exposures to 1 MED of UVB + UVC radiation. Control and pretreated skin sites were again studied and similar protective effects were observed. However, on subsequent reexposure of these sites to 4 MED of UVB + UVC, 14 days after the first of the 5 single MED doses, no significant change in skin blood perfusion was detected at either control or pretreated sites. In a separate series of experiments, LDV data were collected after UVA radiation exposures up to 15 J/cm2. No changes in microcirculation perfusion were detected in any of the situations considered. All LDV measurements were made with 2 instruments of slightly different design and were compared to subjective assessments of erythema performed by a single observer. The results suggest that LDV has significant potential as a means to quantify (1) UV exposures in excess of the MED and (2) the inhibition of UV-induced changes in microcirculatory flow by chemical protectants.     

Pigmentation after single and multiple UV-exposures depending on UV-spectrum

Minimal pigmentation dose (MMD) after a single UV-exposure is well investigated. Whereas only few studies have established MMD after multiple UV-exposures and mainly in fair-skinned persons. The purpose of this study was to establish MMD 1 week after, respectively, one and five UV-exposures in volunteers with a large variation in constitutive pigmentation. A total of 52 volunteers (skin Types II–V) had skin pigmentation quantified by reflectance spectroscopy. They were UV-exposed on the back for 1 and 5 days using a Solar Simulator, narrowband UVB, broadband UVA and UVA1. For all sources a higher dose was needed the more pigmented the skin, except for UVA1. After one UV-exposure, we found a significant positive linear correlation between UV-dose to one MMD, skin type and pre-exposure skin pigmentation. After five UV-exposures the positive linear correlation between UV-dose and MMD and skin type was only significant for narrow band UVB, pre-exposure skin pigmentation was significant also for Solar Simulator. For UVA and particularly UVA1 the MMD was independent of pre-exposure pigmentation. The number of SED to MMD is therefore almost the same for very fair-skinned and dark-skinned persons. Pre-exposure pigmentation was clearly more predictive of MMD than skin type. 50% of MMD equals a pigmentation increase of 1%. The shorter the wavelengths the higher the SED to produce MMD. Solar was the least melanogenic and UVA1 the most melanogenic. For the UVB-sources a higher dose was needed the more pigmented the skin. For UVA the MMD was independent of pre-exposure pigmentation.     

Erythema marginatum in rheumatic fever: Early diagnosis by skin biopsy

A randomized double-blind clinical trial involving twenty-two volunteers was conducted in two locations (Orlando, FL, and St. Paul, MN) to test the efficacy of the newly designed ultraviolet monitor badges (Sun Timers), described in another paper by us in this issue of the Journal,¹ and to establish the relationship between spectral band exposure dose and the biologic responses of erythema and pigmentation. Individuals with skin types II, III, and IV, exhibiting differences in reactivity to solar radiation, were exposed to varying doses of full-spectrum sunlight through templates mounted on the lower portion of the back. Simultaneously, on the upper portion of the back, the same volunteers were exposed through two different types of polyester filters that transmitted ultraviolet A (UVA) and visible radiation. Using templates with windows, exposures to full-spectrum sunlight, UVA, and visible radiation were carried out to 1, 2, 3, 6, and 9 sunburn units (approximately 30–270 millijoules/cm² between 10:30 a.m. and 3:30 p.m. daylight time in mid summer), measured with the aid of a Robertson-Berger meter and an IL700 International Light radiometer. Erythema and pigmentation resulting from these exposures were graded (double-blind) immediately after exposure, at 24 hours, and after 5 days. Numerical skin response ratings at each exposure dose for different spectral bands were then averaged and plotted. It was found that the UVB monitor response was predictive of a 24-hour erythema response and 5-day pigmentation response within 30% of the biologic average for skin types II, III, and IV. UVA radiation stimulated melanogenesis. The minimal melanogenic dose (MMD) for skin type II was the same as the minimal erythemogenic dose (MED). The MMD for individuals of skin types III and IV was distinctly less than their MED. Thus, melanogenesis can be stimulated with a suberythemal dose of UVB or UVA radiation. The sun protection factor values of melanin for melanized skin have been estimated to vary from 1.0 (skin type II) to 4.3 (skin types V and VI).     

UV transmission and UV protection factor (UPF) measured on split skin following exposure to UVB radiation — correlation with the minimal erythema dose (MED)

In this study the ultraviolet (UV) transmission of split skin exposed to UVB radiation and of non-exposed skin was compared in the 280-390 nm wavelength range and quantified. In addition, the correlation between the increase in the minimal erythema dose (MED) associated with a defined exposure to UVB and the ultraviolet protection factor (UPF) calculated from the transmission data was investigated. The study population consisted of 12 patients. Two pieces of split skin of the same thickness (0.3 mm) were taken from the right thigh of each patient. One specimen was removed from an area of non-exposed healthy skin and the other from an area which had been exposed to UVB radiation for a period of 12 days in which the initial dose of 1/3 MED was raised by 1/3 MED every 4 days. The split skin specimens were stretched over a special frame; subsequently, the UV transmission was determined with a spectrophotometer. The mean values obtained for UV transmission were all significantly below the initial data for non-exposed split skin. In the UV range of 280--390 nm, the transmission measured in the exposed specimens was 49.1% of the value measured in the non-exposed split skin (P<0.05). The corresponding values for the UVA range (315--390 nm) and the UVB range (280--315 nm) were 50.1% and 29.5%, respectively (P<0.05), based on the initial transmission data obtained from non-exposed skin. The clinical determination of MED after 12 days of exposure to UVB yielded mean values that were 3.2 times the initial values. Moreover, the mean UPFs calculated from the transmission data measured at the end of the 12-day exposure period were also about three times the initial values. The present study has thus established a significant correlation between the clinical MED values and the UPFs calculated from the transmission data measured following exposure to UVB.     

Evaluating the cytotoxic doses of narrowband and broadband UVB in human keratinocytes, melanocytes, and fibroblasts

Background: No comparative and simultaneous in vitro studies have been performed to determine the cytotoxic dose of narrowband UVB (NBUVB) and broadband UVB (BBUVB) for keratinocytes, melanocytes, and fibroblasts. Culture medium was often replaced with phosphate-buffered saline (PBS) before UV irradiation; however, its amount differed across studies. We determined the cytotoxic doses of NBUVB and BBUVB and tested for changes in viability according to the amount of PBS.
Methods: We exposed cultured human keratinocytes, melanocytes, and fibroblasts to ultraviolet light in the range 12.5–1000 mJ/cm² for NBUVB and 1.25–100 mJ/cm² for BBUVB. The viability was assessed after 24 h. We also determined changes in viability at cytotoxic doses according to the amount of PBS (40, 80, and 120 μl/well in a 96-well plate).
Results: Cytotoxicity was observed at doses of 100, 200, and 400 mJ/cm² for NBUVB and 5, 10, and 25 mJ/cm² for BBUVB in keratinocytes, melanocytes, and fibroblasts, respectively. At cytotoxic doses, there was no change in viability according to the amount of PBS.
Conclusions: Fibroblasts are more resistant to UVB irradiation, irrespective of the amount of NBUVB and BBUVB, than keratinocytes and melanocytes. The amount of PBS during irradiation had no effect on viability.     

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.     

Skin temperature changes induced by ultraviolet A exposure: implications for the mechanism of erythemogenesis

Measurement of the change in skin temperature caused by exposure of the skin to ultraviolet (UV) radiation may give insight into the mechanism responsible for the development of the UV erythema. Under controlled environmental conditions we determined the temperature change of skin areas exposed to UVA, up to 24 h after irradiation. The UVA doses given were 3 or 4 times the minimal erythema dose (MED). The 3-MED and the 4-MED doses resulted in elevation of skin temperature. Delayed UVA erythema was accompanied by skin temperature rise, indicating involvement of arteriolar vessels in the UVA erythema. This arteriolar dilation is best explained if we assume that the delayed erythema is caused by a vasoactive mediator, most likely released in the epidermis, which reaches the dermal blood vessels by diffusion. This result, combined with earlier studies, leads to the conclusion that the erythemas elicited by UVA, UVB and UVC are probably all brought about by diffusing mediators, and not by direct action of the radiation on the blood vessels.