不同波长紫外线照射后皮肤颜色的变化

目的 观察不同波长紫外线照射皮肤后，颜色变化的过程。方法 用双倍剂量最小持续性黑化量和最小红斑量对10例Ⅲ型受试者皮肤进行照射，通过临床评分、扫描反射比分光光度仪和窄谱反射分光光度计三种方法对照射后的皮肤进行14天的评价和测定。结果 UVB照射后，a*值和红斑指数（EI值）在照射后6 h急剧增加，照射后2天达到高峰；L*值在照射后1天出现急剧降低；ITA°在第7天显著降低；黑素指数（MI值）在照射后2天内有逆向的降低趋势，直到照射后7天才有显著增高。在UVA照射下，a*值和EI值改变不明显；L*值在照射后6 h出现显著降低；ITA°在第14天达到最低值； MI值仅照射后1天有显著增高。结论 UVA和UVB照射后的皮肤颜色改变在时间动力学和反应程度方面有明显区别。a*值和EI值是评价照射后日晒伤较为敏感而准确的参数，而ITA°和MI值是评价晒斑较好的参数。     

The evaluation of whitening efficacy of cosmetic products using a human skin pigmentation spot model

Background: To establish a pigmentation spot model on human skin and to assess whitening efficacy for whitening products by this established pigmentation spot model. Methods: Twenty subjects between 20 and 45 years old with skin phototype III or IV were selected. Three consecutive daily UV exposures were performed on buttocks of the subjects as follows: Day 1=1 minimal erythema dose (MED), Day 2=0.5 MED and Day 3=0.5 MED. After the first UV exposure, a selected whitening product was applied to the subjects twice a day on UV exposure area. The application of the whitening product to subjects on the exposed areas was continued till Day 27. CM2500d chromameter, Maxmeter MX18 and visual evaluation were used to assess changes of skin color. Results: A pigmentation spot model after UV exposure was established. The measurement of the pigment spot showed that value declined abruptly at Day 3 and then slowly reached to a lowest point at Day 6. value of the pigment spot almost remained at the same level until Day 20, thereafter increased slowly. The value showed an abrupt increase at Day 3 and slowly reached to a maximal level at Day 6. The value slowly declined toward its baseline level. Likewise, the erythema index also increased significantly at Day 3, and reached to a maximal level at Day 6 and then slowly declined. However, , and erythema indices did not return to their baseline levels during the 27‐day period of this study. On the other hand, value started to increase from Day 3 and such increase was observed continuously to Day 27. Melanin index also showed a slow increase during the first 3 days. It started to increase rapidly from Day 3 and a to maximal level at Day 9 and maintain at a plateau till Day 27 (with an exception at Day 13). To assess the whitening product by this pigmentation spot model, ΔL, , and ΔM values were analyzed. It showed that absolute ΔL value and value of whitening products were lower than those values of the vehicle of the whitening product at each checkpoint, while ΔM value of the whitening product was lower only at Day 9 and Day 20, although no statistically significant differences was found. The visual results also strongly supported that the whitening product enhanced the decrease of pigmentation. Conclusion: This study showed that repeated UV exposure was able to induce a long extensive period of pigment formation. The resulted pigmentation spot was able to maintain at an elevated level till Day 20. Clinical subjective evaluations together with combined objective instrument measurements were still important to assess whitening and spot‐removing ability of a material due to the instrument limitation for color differentiations. This kind of pigmentation spot model can be used to assess whitening efficacy for whitening or spot‐removing products. In addition, the combinations of subjective and objective methods were able to serve as advisable references to assess the whitening efficacy of products.     

Different narrowband UVB dosage regimens in dark skinned psoriatics: a preliminary study

Background: Psoriasis is a common and relapsing disease, which is both physically and psychologically disabling. Narrowband UVB (NB‐UVB) is used in fair‐skinned population in suberythemogenic doses with good results; however, in the darker skin population (skin types III, IV, V) erythemogenic doses have not been thoroughly investigated. Aim: A left–right bilateral comparative trial was carried out to compare the suberythemogenic dose of NB‐UVB vs. erythemogenic dose in the treatment of dark‐skinned psoriatic patients. Patients and methods: The study was conducted on 20 patients with chronic plaque psoriasis. The left side was treated with the dose causing minimal erythema [100% of minimal erythema dose (MED)] while the right side received 70% of this MED (suberythemogenic side). Results: Our results revealed no statistically significant difference in PASI final and in the percentage of reduction of PASI score between both sides as well as the total number of sessions (P‐value>0.05), while the total cumulative UVB dose on the suberythemogenic side was significantly lower (P‐value<0.001). Conclusion: Our study recommends reducing the dose regimen of NB‐UVB and consequently the cumulative UVB dose by using the suberythemogenic dosing schedule even in dark skin population.     

Time course of ultraviolet-induced skin reactions evaluated by two different reflectance spectrophotometers: DermaSpectrophotometer and Minolta spectrophotometer CM-2002

BACKGROUNDS: Many attempts have been made to quantify ultraviolet (UV)-induced erythema and pigmentation, but most studies have been focused on the initial changes of reaction for a few hours or days and neglected the later events. METHODS: : A time course of skin colour changes induced by fluorescent sunlamp with a broad band of UVA and UVB radiation was evaluated in 15 Korean male volunteers using two different reflectance spectrophotometers for 28 days. The results were presented by E (erythema)- and M (melanin)-index as well as values converted to the L*a*b* system recommended by the CIE (Commission Internationale de l'Eclairage). RESULTS: The mean individual typology angle of the subjects was 46.6 degrees, which indicated "light" group in constitutional skin colour category. A day after UV exposure, the L* and b* values decreased significantly, following the colour direction of persistent pigment darkening. The values went in the opposite direction persistently until after the 1st week, when maximum tanning was obtained. They then shifted toward their original positions, parallel to the constitutive melanization axis. The a* index showed a significant increase toward the mean colour of haemoglobin on day 1. It returned to its original value along the constitutive melanization axis. The E-index showed a maximum value at day 1, then returned to baseline. The value of M-index reached a peak at day 7. There was no significant difference between the two instruments, but each has its own characteristic features. CONCLUSION: These promising quantitative methods should enable us to achieve objective measurement of the dermatophysiologic changes and to evaluate the efficacy of therapeutic modalities on skin disorders without the inherent errors associated with subjective judgement. Our results provide standard data on a time course of UV-induced skin erythema and pigmentation.     

Topical isoflavones provide effective photoprotection to skin

Background/purpose: Isoflavones, one main group of phytoestrogens, have antioxidative and photoprotective effects in cellular and mouse studies. The aim of this study is to obtain a more comprehensive understanding of the isoflavone‐mediated photoprotection with the pig skin model, a more human‐resembling model. Methods: The pig skin was treated with five well‐known isoflavone compounds (genistein, equol, daidzein, biochanin A, and formononetin) and one antioxidant combination solution of 15% vitamin C and 1% vitamin E and 0.5% ferulic acid (CEF) daily for 4 days. Skin was irradiated with solar‐simulated UV irradiation, 1 to 5 minimal erythema dose (MED) at 1‐MED intervals. Evaluation was carried out 24 h later by colorimeter‐measured erythema and sunburn cell numbers. Results: Topical application of 0.5% solutions of three individual phytoestrogens – genistein, daidzein, biochanin A – are better than similar solutions of equol or formononetin in protecting pig skin from solar‐simulated ultraviolet (SSUV)‐induced photodamage, as measured by sunburn cell formation and/or erythema. However, the protection was less than that provided by a topical combination antioxidant standard containing 15% L‐ascorbic acid, 1%α‐tocopherol, and 0.5% ferulic acid. Conclusion: Isoflavones provide effective photoprotection and are good candidate ingredients for protection against ultraviolet (UV) photodamage.     

A long-term time course of colorimetric evaluation of ultraviolet light-induced skin reactions

Many attempts have been made to quantify ultraviolet (UV) radiation-induced erythema and pigmentation. However, most of these studies were concerned with the early changes of reactions and neglected events occurring in later stages. The long-term course of skin colour changes in pigmented skin, induced by broad band UVA and UVB radiation, was evaluated in 30 Korean male volunteers by means of a tri-stimulus colorimeter for 10 weeks. The L*a*b* system recommended by the Commission International de l'Eclairage was used to measure skin colour. The L* value (luminance) gives the relative lightness ranging from total black to total white. The a* value represents the balance between red and green and the b* value the balance between yellow and blue. The mean individual typology angle of our subjects was 47.3 degrees, indicating 'light' group of constitutional skin colour category. One day after UV exposure, the L* and b* values decreased significantly, following the colour direction of persistent pigment darkening. They then changed in opposite directions persistently until week 1, when maximum tanning was obtained. Then, a shift toward the original values was observed parallel to the constitutive melanization axis. The a* index showed a significant increase toward the mean colour of haemoglobin on day 1. It returned to its original value following the pathway of constitutive melanization axis. This promising quantitative method may enable objective measurement of dermatophysiologic changes to be made, and allow evaluation of the efficacy of therapeutic modalities on skin disorders without the inherent errors associated with subjective judgement. Our results would provide standard data for long-term UV-induced skin erythema and pigmentation.     

An action spectrum for the elicitation of erythema in skin persistently sensitized by photobound 8-methoxypsoralen

Human skin can be rendered persistently photosensitive by topical application of aqueous 8-methoxypsoralen (8-MOP) and exposure to a suberythemogenic dose of more than 380 nm radiation. We report an action spectrum for the elicitation of phototoxic erythema induced by a second exposure of skin pretreated in this way. After correction for unsensitized skin erythema this action spectrum resembles the absorption spectrum of the 4',5'-monoadduct of 8-MOP to DNA. This suggests that the monoadduct is the chromophore for erythema elicited by the second irradiation, and supports the DNA crosslink as the crucial photoproduct causing phototoxic erythema due to 8-MOP in human skin.     

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.     

Med estimation for narrow band UV-B on type IV and type V skin in India

With an aim to determine minimum erythema dose of narrow band UV-B, 30 subjects, 20 with type IV skin and 10 with type V skin were subjected to graded incremental doses of 311-Narrow band UV-B phototherapy cabiner by Daavlin. Barely perceptible erythema 24 hours after exposure was taken as MED. 33.3% developed erythema at 745 mj, 26.6% at 620 mj, 23.3% at 1075 mj, and 10% at 1290 mj. The average MED for narrow band UV-B exposure for type 1V skin was 600 mj, [range 5515-755 mj] and for type V skin 1100 mj {range 895-1290 mj}. Better therapeutic response can be obtained by giving approximately 360-450 mj as initial irradiation dose for type 1 V skin and 600-825 mj for type V skin.     

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.     

人工紫外线诱导正常皮肤色素斑的初步研究

目的:建立人工紫外线诱导正常皮肤色素斑的模型。方法:采用日光模拟器人工光源,以连续紫外线(波段290～400nm)照射健康受试者上臂内侧皮肤,观察不同照射剂量及照射后不同测量时间局部皮肤黑素测量值的变化。结果:照射后1周,2.0倍最小红斑量(MED)照射剂量组产生黑素的强度高于1.5MED组(P<0.05),与2.5MED组的差异无统计学意义(P>0.05);2.0MED组红斑消退及表面光滑度较2.5MED组轻(P<0.05),与1.5MED组差异无统计学意义(P>0.05)。紫外线照射后1周,各剂量组黑素测量值(L值)均达到高峰,其后随时间延长迅速下降(P<0.05),在第4、5周下降趋势变缓(P>0.05);而红斑测量值(a值)在紫外线照射1周时达到高峰后呈持续递减趋势(P<0.05)。结论:2.0MED照射剂量是紫外线在正常皮肤诱导色素斑的最佳剂量,照射后1～4周是观察色素变化的最佳时机。     

An action spectrum for photoinduction of prolonged cutaneous photosensitivity by topical 8-MOP

Suberythemogenic exposure of human skin treated with aqueous 8-MOP to radiation greater than 380 nm prolongs photosensitization to subsequent UVA from 6 to 24-72 h. One hypothesis for prolonged photosensitization is that greater than 380 nm irradiation forms 8-MOP-DNA monoadducts, which are removed more slowly than free 8-MOP and serve as a substrate for crosslinking by further UVA exposure. Sufficient DNA crosslinking results in erythema. We have examined this hypothesis by measuring the action spectrum for induction of prolonged photosensitization. Skin of normal volunteers was treated with aqueous 8-MOP (0.003%) and immediately received suberythemogenic monochromatic exposures between 334 and 430 nm. twenty-four hours later, the presence of prolonged sensitization was tested by small exposures of UVA. Erythema was evaluated 3 and 5 d later, and an action spectrum for prolonged sensitization was determined. The minimum phototoxic dose (MPD) was also determined at each wavelength. The action spectrum for prolonged photosensitization declined gradually between 334 and 425 nm. The action spectrum for delayed erythema induced by a single exposure of 8-MOP-treated skin declined rapidly from 334-390 nm. These findings are consistent with prolonged binding of 8-MOP in the skin by an initial exposure, possibly as 8-MOP-DNA monoadducts, allowing the second exposure to induce an erythemogenic event, possibly crosslinking of DNA.     

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.     

Dose-response and time-course characteristics of UV-A1 erythema

OBJECTIVE: To determine the time course and dose-response characteristics of UV-A1 erythema in the Tayside region of Scotland. DESIGN: Adult volunteers (skin types I and II [n = 13] and III and IV [n = 11]) were exposed to geometric dose series of UV-A1 irradiation from a high-output source on photoprotected lower back and inner forearm skin. SETTING: Photobiology unit in a university hospital. MAIN OUTCOME MEASURES: The minimal erythema dose (MED) was recorded visually and erythema was assessed objectively by erythema meter at 4, 8, 24, and 48 hours after exposure. RESULTS: Peak erythema (lowest visual MED) was seen at 8 hours on the back and arm in 11 subjects with skin types I and II and on the back at 8 hours in 9 subjects and on the arm at 4 hours in 10 subjects with skin types III and IV. The lowest median (range) MED was 20 J/cm(2) (14-56 J/cm(2)) on the back and 42 J/cm(2) (20 to >80 J/cm(2)) on the arm at 8 hours for subjects with skin types I and II and 28 J/cm(2) (20-112 J/cm(2)) at 8 hours on the back and 56 J/cm(2) (28-80 J/cm(2)) at 4 hours on the arm for subjects with skin types III and IV. The D(0.025), an objective measure that corresponds approximately to the visual MED, demonstrated a broad peak from 8 to 24 hours. CONCLUSIONS: Our local population is more erythemally sensitive to UV-A1 radiation than reports suggest. Daily dose regimens may risk cumulative erythema. Lower starting doses should be used in this population. The wide range of MEDs highlights the need for MED testing.     

Melanin differentially protects from the initiation and progression of threshold UV-induced erythema depending on UV waveband

BACKGROUND/PURPOSE: This study aimed to determine the relationship between various measures of constitutive skin pigmentation and erythema caused by solar-simulated UV (ssUV), 290 and 310 nm UV. METHODS: Skin pigmentation was assessed clinically by skin typing as well as objectively by measurement of the melanin index (MI) by reflectance spectroscopy. Subjects having Fitzpatrick skin types I-IV were exposed to graded doses of ssUV and either narrowband 310 nm (n=70) or 290 nm (n=69) UV, and assessed 24 h after exposure. Minimal erythema dose (MED) was assessed visually as the lowest dose that caused minimally perceptible erythema. Susceptibility to further development of erythema with higher exposure doses was measured by the gradient of erythema dose-response curves. This was determined by linear regression using reflectance spectrometry data beyond the MED. RESULTS: Although there was considerable variation within each skin type, MI and ssUV MED increased with increasing Fitzpatrick skin type. MI correlated with ssUV MED and 310 nm UV MED, but not 290 nm UV MED. There was also a significant negative correlation between MI and erythema dose-response gradients caused by ssUV, 310 and 290 nm UV. CONCLUSION: Melanin situated near the basal epidermis may not protect from the initial development of threshold erythema caused by 290 nm UV because it penetrates poorly past the stratum corneum and is not well absorbed by melanin in vivo compared with 310 nm UV. Higher erythemal 290 nm UV doses may reach basal epidermal melanin, which may then afford protection against further 290 nm UV erythema.     

Erythema and melanogenesis action spectra in heavily pigmented individuals as compared to fair-skinned Caucasians

The protective role of epidermal melanin pigmentation against chronic exposure to ultraviolet radiation is widely accepted, although its photoprotective effect against acute exposure is less certain. In this study, the action spectra of erythema and melanogenesis in heavily pigmented individuals (skin type V) were determined at 295, 305, 315, and 365 nm, and compared with those of skin types I and II. When the erythema and melanogenesis action spectra for skin type V were normalized to 295 nm, they were identical to the corresponding action spectra for fair-skinned individuals, indicating that the photoprotection of epidermal melanin pigmentation is essentially independent of wavelength. The ratio of values for the minimum erythema dose (MED) between skin type V and skin types I and II was 2.29, which is close to the ratio of pigment in these skin types, as measured by diffuse reflectance spectroscopy in the visible range. The minimum immediate pigment darkening dose (IPD) and the minimum melanogenic dose (MMD) at 365 nm, and the MED and MMD at 315 nm were the same for all skin types, while the variation of MED for every skin type was maximum at 305 and 365 nm. The results provide circumstantial evidence that erythema and melanogenesis have the same mechanism at short-wavelength UVB (295 and 305 nm), and different mechanisms in UVA (365 nm). Furthermore, the 24 h MED at 305 nm appears to be a sensitive indicator of skin type.     

The protective role of epidermal melanin in a patient with porphyria variegata and vitiligo

To assess the role of epidermal melanin in a patient with porphyria variegata and vitiligo, the MED was determined in pigmented and vitiliginous skin for wavelengths of 310, 405 and 500 nm. The energy required to elicit erythema by irradiating vitiliginous skin at 310 nm was half that for pigmented skin. For 405 nm the differences was 4-fold and at 500 nm 2-fold. A possible explanation for the different protection by melanin against light of 310, 405 and 500 nm is given. UV-B irradiation, as a potent stimulus for melanization of the skin, is proposed as an additive measure in the protection against photosensitivity reactions in porphyria patients.     

Effects of solar-simulated radiation dose fractionation on CD1a+ Langerhans cells and CD11b+ macrophages in human skin

BACKGROUND: There are few human studies investigating the immunosuppressive effects of exposure to solar-simulated radiation (SSR) and its relationship with sunburn/erythema, and few comparative data on the importance of SSR exposure regimens. OBJECTIVES: To evaluate whether SSR-induced erythema is a reliable end-point for assessing damage to antigen-presenting cells (APCs) in human skin. METHODS: We compared the relationship between SSR-induced erythema and alterations in epidermal CD1a+ Langerhans cells (LCs) and CD11b+ macrophages in human volunteers after single exposures to 0, 0.5, 1, 2 or 3 minimal erythema doses (MED). We also investigated whether SSR exposure leads to an accumulation or accommodation of the same end-points by comparing the effects of a relatively low cumulative SSR dose (3 MED) given in varying daily dose fractions (4 x 0.75 MED, 2 x 1.5 MED and 1 x 3 MED). RESULTS: Single SSR exposures induced a dose-dependent increase in erythema. CD1a+ LCs remaining in the irradiated epidermis showed a dose-dependent increase in cell size and altered morphology. Significant depletion of CD1a+ LCs and presence of CD11b+ macrophages only occurred in sites irradiated with 2 MED and 3 MED. Dose fractionation had no effect on the final erythemal response but the 4 x 0.75 MED and 1 x 3 MED protocols were better tolerated than 2 x 1.5 MED for alterations in CD1a+ LC and CD11b+ cell numbers. In contrast, dose fractionation protected against alterations in CD1a+ LC morphology or cell size. CONCLUSIONS: We found that erythema is a poor indicator of alterations in epidermal APCs and that dose fractionation is an important parameter in the immunological effects of ultraviolet radiation.     

Photoadaptation during narrowband ultraviolet-B therapy is independent of skin type: a study of 352 patients

Understanding how photoadaptation differs between individuals is important when considering susceptibility to the beneficial and harmful effects of sunlight exposure and when determining optimal phototherapy regimens. Most narrowband UVB (NB-UVB) regimens start with 70% of the minimal erythema dose (MED) with 20% increments at each treatment thereafter. We retrospectively studied 352 skin types I-IV psoriatic patients having twice weekly treatment with this regimen. Patients with high skin types tended to have high MEDs (P<0.001). By session 20 the proportion of patients who had developed erythema was approximately 60% regardless of MED. Among patients who developed erythema, the number of treatments before erythema occurred did not differ between skin types (P=0.33). We conclude that patients with high skin types photoadapt approximately equally per physical unit of UVR in comparison to those with low skin types, but they have greater photoadaptation in absolute terms because they are able to tolerate a higher initial dose of radiation. Differences in skin type or MED are not associated with clinically important differences in tendency to erythema during a standard 70/20% NB-UVB twice-weekly regimen. This regimen is suitable for all skin types I-IV patients regardless of skin type or MED.     

Med estimation for narrow band UV-B on type IV and type V skin in India

With an aim to determine minimum erythema dose of narrow band UV-B, 30 subjects, 20 with type I V skin and 10 with type V skin were subjected to graded incremental doses of 311-narrow band UV-B phototherapy cabinet by Daavlin. Barely perceptible erythema 24 hrs after exposure was taken as MED. 33.3% developed erythema at 745mj, 26.6% at 620mj, 23.3% at 1075mj, and 10% at 1290mj. The average MED for narrow band UV-B exposure for type I V skin was 600mj, [range 515-755mj] and for type V skin 1100 mj [range 895-1290mj] Better therapeutic response can be obtained by approximately 360 -450mj as initial irradiation dose for type IV skin and 600-825mj for type V skin.