Does the minimal phototoxic dose after 8‐methoxypsoralen baths correlate with the individual’s skin phototype?

BACKGROUND/AIMS: Up to now no data have been available concerning whether there is a significant correlation between skin phototypes and the minimum phototoxic dose (MPD) after bath water delivery of 8-MOP. METHODS: The skin phototype of each of 46 patients was determined based on the individual past history of solar-induced burning and tanning. In addition, the MPD of each patient was assesed after photosensitization with a warm water bath (37 degrees C, 98.6 degrees F) containing 1.0 mg/l 8-methoxypsoralen (8-MOP). Statistical analysis was performed using a Mann-Whitney U-test and Spearman rank order correlation. RESULTS: The median MPD in patients with skin phototype II was 2.0 J/cm2 (range < or =0.5 to > or =3.5) versus 1.5 J/cm2 (range 1.0 to > or =3.5) in patients with skin phototype III. There was a considerable overlap between both groups. No significant difference was detected comparing both groups (P=0.7326) and Spearman rank order correlation revealed no correlation between skin phototype and MPD. CONCLUSION: Erythemal sensitivity in PUVA bath therapy, measured as MPD, is not correlated with sun-reactive skin phototype in skin types II and III. Thus skin phototype is not a suitable indicator for the initial UVA dose in PUVA bath photochemotherapy.     

Comparison of minimal phototoxic dose and skin type for determining initial UVA dose in oral liquid methoxsalen photochemotherapy for the treatment of psoriasis.

Twenty-five patients with extensive psoriasis were randomly assigned into one of three groups, each receiving 0.5 mg/kg of oral liquid methoxsalen photochemotherapy followed 1 h later by exposure to long-wave ultraviolet light (UVA). The sole difference between the three groups was the method used to determine the initial UVA dose, which was either based on skin type, 25% of the minimal phototoxic dose (MPD), or 50% of the MPD. All patients were treated in the Phototherapy Unit at the Massachusetts General Hospital. Data were obtained until reaching the endpoint of clearance. At clearance, the results of the number of treatments required to clear, final UVA dose, cumulative UVA dose, and side effects were tabulated, compared, and analyzed for each of the three groups. The 25% and 50% MPD groups required a mean of 15.0 +/- 1.7 and 13.4 +/- 1.9 treatments to clear, respectively, as compared to the skin type group, which needed an average of 17.6 +/- 2.5 treatments. The mean final UVA dose was 7.4 +/- 0.9 J/cm2 and 8.4 +/- 1.4 J/cm2 for the 25% and 50% MPD groups, respectively, in contrast to 11.6 +/- 1.4 J/cm2 for the skin type group. The mean cumulative UVA dose at clearance for the 25% and 50% MPD groups was 79 +/- 16 J/cm2 and 87 +/- 27 J/cm2, respectively, versus 136 +/- 30 J/cm2 for the skin type group. The comparisons between the individual MPD groups and the skin type group did not achieve statistical significance with the exception of a marginally significant difference in final dose between the skin type group and the 25% MPD group (p = 0.06). However, the results of the two MPD groups were then pooled and the mean final (7.9 +/- 0.8 J/cm2) and cumulative (83 +/- 15 J/cm2) UVA doses were significantly (p = 0.04) and marginally significantly (p = 0.07) lower than the respective means of the skin type group. The number of treatments to clear, although lower in the pooled MPD groups (14.2 +/- 1.3) than in the skin type group, did not attain statistical significance (p = 0.19). Our data suggest that the MPD measurement may be superior to the skin-typing system when calculating the initial UVA dose in oral liquid methoxsalen photochemotherapy for the treatment of psoriasis.     

Time course of skin photosensitivity following trimethylpsoralen bath PUVA

One aspect of bath photochemotherapy (PUVA) that requires clarification is the duration of psoralen-induced cutaneous photosensitisation under conditions simulating clinical use. Using a half back comparison study technique, we investigated the persistence of trimethylpsoralen (TMP)-induced photosensitivity in skin irradiated to simulate a first PUVA exposure compared with un-irradiated skin. Baseline UVA minimal erythema dose and minimal phototoxic dose (MPD) were determined in 13 healthy volunteers. After readings at 72 h, subjects were bathed in TMP bath water for 15 min and one half of the back was immediately exposed to 40% of the MPD. Test sites (1.5 cm2) on both halves of the back were then irradiated with a UVA dose series at 15 min, 5, 10, 24, 34, 48 and 72 h after the bath. MPD readings were recorded visually at 72 h after each UVA exposure. The UVA MED was >25 J/cm2 in all the subjects. At each time point, a phototoxic index (PI) was calculated as UVA MED/MPD. In un-irradiated skin, photosensitivity returned to normal (PI=1) within 24 h after the TMP bath. In contrast, skin pre-irradiated to simulate the first PUVA treatment was still significantly photosensitive (PI=2.3; P=0.002) at 48 h. Contrary to previous recommendations, these data suggest that patients should be advised to avoid ambient or artificial sources of UVA throughout their course of TMP bath PUVA to reduce the risk of phototoxic erythema.     

Large increments in psoralen-ultraviolet A (PUVA) therapy are unsuitable for fair-skinned individuals with psoriasis

The ideal psoralen-ultraviolet A (PUVA) regimen for chronic plaque psoriasis has yet to be established. There are four components to a PUVA regimen: the dose of psoralen, the starting dose of UVA, the frequency of treatment and the incremental UVA dose protocol. Recent studies have been directed at trying to optimize the efficacy of PUVA while minimizing acute side-effects and the risk of cutaneous carcinogenesis, believed to be independently related to the cumulative dose of UVA and the total number of treatments. The British Photodermatology Group recommends two twice-weekly PUVA regimens: one starts with 50% of the minimal phototoxic dose (MPD) and uses weekly increments of 40%, 30%, 25%, 20%, 15%, 10% and 5% of the previous dose to a maximum of 14.5 J/cm2; the other starts with a fixed dose based on skin type and uses weekly dose increments of 40%, decreasing to 20% once erythema develops. We undertook a prospective randomized controlled trial comparing these regimens in 85 Irish patients. The clearance rate with the MPD regimen was lower than with the skin type regimen, 67.5% vs. 95% (P < 0.05). The reasons for treatment failure were grade 3 erythema and severe PUVA itch. There was a trend suggesting that patients with skin types I and II, but not skin type III, required a higher cumulative UVA dose and fewer exposures to clear with the MPD regimen than the skin type regimen, although this did not reach statistical significance. Grades 2 or 3 erythema were very common in both treatment groups (52. 5% of the skin type group and 45% of the MPD group). This is the third study to suggest that patients with skin types I and II receive a higher total UVA dose when the starting dose is 50-70% of the MPD (rather than 0.5 J/cm2 for skin type I and 1.0 J/cm2 for skin type II) and when large dose increments are used. We suggest that smaller dose increments should be used in patients with skin types I and II.     

Assessment of minimal phototoxic dose following 8-methoxypsoralen bath: maximal reaction on average after 5 days

An essential procedure before starting bath psoralen ultraviolet (UV) A (PUVA) photochemotherapy is the evaluation of the minimal phototoxic dose (MPD), which is traditionally assessed 3 days after irradiation. However, there are no controlled studies supporting the 72 h peak of bath-PUVA erythema. The aim of this study was therefore to determine the exact time course of the erythematous reaction in human skin following bath-PUVA. For this purpose, the skin of 10 volunteers was exposed to 0.5-3.0 J/cm2 UVA directly after a 20-min 8-methoxypsoralen bath (0.5 mg/L, 37 degrees C). At 24, 48, 72, 96, 120 and 144 h (1-6 days) after irradiation, the MPD and the erythema sum score (ESS) were determined in each subject. The results showed a maximal erythematous reaction on average 5 days after irradiation. The mean MPD gradually decreased from day 2 (> 3.0 J/cm2) to day 5 (mean +/- SD 1.15 +/- 0.63 J/cm2) and started to increase at day 6 (mean +/- SD 1.6 +/- 0.52 J/cm2). The mean +/- SD ESS correspondingly increased from day 2 (0 +/- 0) to day 5 (10.5 +/- 3. 7) with a decrease at day 6 (7.5 +/- 3.1) (difference between day 3 and beyond statistically significant at P < 0.05). As our study indicates a maximal erythematous reaction to the bath-PUVA up to 5 days after irradiation, the traditional MPD assessment at 3 days generates a risk of phototoxic side-effects within the phototherapy course by underestimating the phototoxic effect in some patients. These findings contribute towards a more defined understanding of the kinetics of the phototoxic reaction in bath-PUVA therapy.     

Interaction of commonly used emollients with photochemotherapy

BACKGROUND/AIM: Even though emollients are commonly used in combination with photochemotherapy, we still lack guidance for the selection of the appropriate emollient to be used in combination with photochemotherapy. The purpose of our study was to determine the interaction of commonly used emollients with photochemotherapy. METHODS: The study was carried on 75 healthy volunteers. In order to assess the effects of five different emollients--white petrolatum, 3% salicylic acid in white petrolatum, Balmandol, Decubal and Urederm hydro--the subjects were divided into five groups. Minimal phototoxic dose (MPD) was determined by irradiating two rows of six circular test fields on the back of the subjects with increasing doses of UVA. One of the emollients listed above was applied to the skin under the upper rows alternatively, whereas the lower rows served as control. RESULTS: Application of Urederm hydro and Decubal before exposure to UVA resulted in a statistically significant decrease in the MPD in all subjects. Even though application of white petrolatum and white petrolatum containing 3% salicylic acid decreased the MPD in most of the subjects and Balmandol application slightly increased the MPD, the results did not reach statistical significance. CONCLUSIONS: According to our findings, it is probable that the total dose of UVA needed to cause clearing of psoriasis would be decreased by application of Urederm hydro and Decubal prior to photochemotherapy. We noted a slight photoprotective effect of Balmandol in the UVA range, but this finding has to be further studied. Clinical studies are needed to clarify the effects of these emollients on the course and outcome of photochemotherapy.     

8-MOP PUVA for psoriasis: a comparison of a minimal phototoxic dose-based regimen with a skin-type approach

Summary Two ultraviolet A (UVA) regimens for oral S-methoxypsoralen (8-MOP) photochemotherapy (PUVA) for moderate/severe chronic plaque psoriasis using a half body study technique were compared. Each patient received both regimens. A higher-dose regimen based on minimal phototoxic dose (MPD) within percentage incremental increases was given to one-half of the body. The other half received a lower dose regimen based on skin type with fixed incremental UVA increases. Patients were treated twice weekly. Symmetrical plaques were scored to determine the rate of resolution with each regimen. In addition, the number of treatments, cumulative UVA dose and number of days in treatment to achieve overall clearance were recorded. Patients were reviewed monthly for 1 year to record remission data. Thirty-three patients completed the study. Both regimens were effective and well tolerated. With the MPD-based approach, the number of exposures was significantly less for patients with skin types I and II but not III. Although the cumulative UVA dose was higher with the MPU regimen for all skin types studied, the reduced number of exposures required for clearance for skin types I and II but not III, combined with thesecurity of individualized MPD testing, has practical attractions. MPD testing also identified live patients who required an increased psoralen dose and six patients who required a reduction of the initial UVA dose with the skin type regimen. Forty-two per cent were still clear 1 year after treatment and there was no significant difference in the number of days in remission between the regimens for those whose psoriasis had recurred. The reduction in the number of exposures required lor clearance with the MPD-based regimen may be safer and more cost effective in the long term.     

Coal tar phototoxicity: kinetics and exposure parameters

We examined two manifestations of coal tar phototoxicity: delayed erythema and skin pain (tar smarts) by quantifying the amount (dose) of UVA and exposure conditions required to induce these phenomena in normal human skin. The minimal UVA dose required to induce delayed erythema (minimal phototoxic dose or MPD) and the minimal UVA dose required to induce an immediate smarting reaction (minimal smarting dose or MSD) were recorded in 32 subjects in a variety of settings. A log-log dose-response model described the relation between the interval of time tar was left on the skin and lowering of MPD. We examined 4 different methods of tar removal and showed that several methods using more than water alone were equally effective--judging by resultant phototoxicity. The time between tar removal and UVA irradiation is important. Even 30 min was sufficient for the MPD to increase from 3.77 +/- 1.55 to 6.1 +/- 4.0 J/cm2 (p less than 0.02). The smarting reaction shows a similar dependence on the time interval between tar removal and exposure. The mean MSD was less than the mean MPD at all times tested. Both manifestations of coal tar phototoxicity, reduced delayed erythema threshold and susceptibility to the smarting reaction, persisted at least 30 h after tar removal.     

Cutaneous carcinoma and PUVA lentigines in Thai patients treated with oral PUVA

A total of 113 Thai patients who were treated with oral PUVA from 1979 to 1992 were examined for long-term cutaneous side effects of PUVA. Two psoriatic patients developed PUVA keratosis on non-sun-exposed areas. Both were skin type IV and had had phototherapy with UVB and sunlight previously. The total doses of UVA were 909 J/cm² and 242 J/cm² respectively. One psoriatic patient developed Bowen's disease. He had had a cumulative dose of UVA 2207 J/cm². He also had a past history of arsenic intake and phototherapy with UVB and sunlight. PUVA lentigines were seen in 58 patients (51.4%). It was associated with older age at starting PUVA, higher cumulative UVA dose and greater number of PUVA treatment. This study suggests that previous exposure to other risk factors is important for inducing skin cancer in populations with skin phototype III, IV and V treated with oral PUVA.     

Diffuse reflectance spectrophotometry for skin phototype determination

Background: The Fitzpatrick skin phototype classification scheme has become the standard method for assessing the reaction of the skin to solar stimuli; this method can be easily biased by different factors, such as ethnicity or chronic sun exposure. Methods: Diffuse reflectance spectrophotometry (DRS) is an objective and non‐invasive method used in this work to determine constitutive skin color from the upper volar arm as an objective way of measuring skin pigmentation. A DRS‐determined melanin index that accounts for skin pigmentation was obtained for 35 subjects of Hispanic origin, this melanin index was compared with the physician‐diagnosed and self‐reported skin phototypes. Results: The results show that at least for Hispanic individuals, there is a clear clinical distinction between subjects with skin phototype I and their DRS‐determined melanin index; however, subjects with skin phototypes II–VI have a large melanin index overlap. Conclusion: Clinical assessment of skin phototype can be complemented by using DRS.     

Relevance of skin phototyping to a Korean population

We have determined skin phototype by a self-reporting questionnaire proposed by Fitzpatrick in 128 Korean medical students. We also measured the minimal erythema dose (MED), minimal melanogenic dose and investigated their relationship to phototype. A questionnaire of skin phototypes revealed that 13.3% of the students are skin phototypes I and II. Based on MEDs, we demonstrated that 14.8% of the students fall into the UV-sensitive group as defined by an MED of less than 40 mJ/cm² which is the upper range of MED of phototypes I and II in a white population. The skin phototypes did not show a positive correlation to MEDs and only 2.3% of students classified as skin phototypes I and II showed an MED below 40mJ/cm². This study indicates that the skin phototyping method proposed by Fitzpatrick does not reliably predict UV-sensitive individuals within the Korean population.     

Comparison of turbo‐PUVA and conventional American‐style PUVA in the treatment of psoriatic patients

Background: Ultraviolet (UV)A protective properties of dihydroxyacetone (DHA) have been used as a topical UV‐resisting barrier to optimize psoralens and UVA (turbo‐PUVA). Starting doses and increments were based on the DHA diffuse reflectance spectroscopy‐derived protection factor. Objective: To evaluate the efficacy of turbo‐PUVA in psoriatic patients using a simpler method for determining starting doses and increments, in comparison to the conventional American‐style PUVA photochemotherapy. Methods: Thirty psoriasis patients (15 on American‐style PUVA and 15 on turbo‐PUVA) were evaluated, each receiving PUVA twice weekly. Starting UVA dose was determined according to skin phototype for the American‐style PUVA group and according to the patient's skin phototype × DHA SPF 3 in turbo‐PUVA group. UVA increments used were 0.5–1.5 J/cm² per treatment in American‐style PUVA and 25% of the previous dose in turbo‐PUVA. Results: Turbo‐PUVA group showed a significantly lower mean cumulative dose, a significantly higher psoriasis area and severity index score reduction, lesser mean number of treatment sessions, and less duration of treatment till remission (188.44±106.2 J/cm², 92.164±1.975%, 11.2±3.52 session, and 1.4±0.44 months, respectively) than conventional American‐style PUVA group (255.13±18.304 J/cm², 74.725±10.976%, 30±0.00 sessions, and 3.75±0.00 months, respectively). Conclusion: Turbo‐PUVA is more effective and time convenient for the treatment of psoriasis with less cumulative dose than the conventional American‐style PUVA.     

Correlation between 8-methoxypsoralen bath-water concentration and photosensitivity in bath-PUVA treatment

BACKGROUND: Bath-PUVA treatment, originally established in Scandinavia, offers several advantages over oral PUVA and has become increasingly popular in recent years. Outside Scandinavia 8-methoxypsoralen (8-MOP) is the prevailing photosensitizer for this PUVA modality and is used arbitrarily in a wide range of concentrations. Up to the present, data are lacking on the impact of 8-MOP bath-water concentration on UVA dosimetry. OBJECTIVE: We investigated the influence of increasing 8-MOP bath-water concentrations on photosensitivity in bath-PUVA treatment. METHODS: Fifteen healthy volunteers without abnormal photosensitivity or recent exposure to ultraviolet radiation were included in an intraindividually controlled comparison study. In all volunteers the minimal phototoxic dose (MPD) was determined on the volar side of their forearms after immersion for 20 minutes in 4 different 8-MOP bath-water concentrations (0.5, 1, 2.5, and 5 mg/L). The correlation between 8-MOP concentration and photosensitivity (defined as the reciprocal value of the MPD) was analyzed by linear regression analysis. In addition, the time course of erythema formation and the UVA dose-erythema response curve was assessed for each psoralen concentration. RESULTS: The median MPD and the 25%-75% interquartile were 5.7 J/cm(2) (5.7-8), 4 J/cm(2) (4-5.7), 2.8 J/cm(2) (2.8-5.7), and 2 J/cm(2) (2-2.8) at an 8-MOP concentration of 0.5, 1, 2.5, and 5 mg/L, respectively. Linear regression analysis revealed a significant correlation between 8-MOP bath-water concentration and photosensitivity (r = 0.98; P =.019). Bath-PUVA-induced erythema peaked after a median time interval of 3 days, with a range of 2 to 4 days. The slope of the UVA dose-erythema response curve was similar for all psoralen concentrations. CONCLUSION: UVA dose requirements in bath-PUVA treatment decrease linearly with increasing 8-MOP concentrations. A single MPD assessment at 72 hours after the UVA exposure is inappropriate for accurate determination of the patients' photosensitivity. The hazard of wrong UVA dosimetry is comparable at all psoralen concentrations.     

Evaluation of narrow band ultraviolet B phototherapy in the treatment of chronic actinic dermatitis in Chinese patients

Few studies have been conducted in chronic actinic dermatitis (CAD) treated with narrowband ultraviolet B (NB UVB) phototherapy, especially in Asian patients. We aim to evaluate the efficacy and safety of NB UVB phototherapy in Chinese patients with CAD. 19 CAD patients of Fitzpatrick skin phototype IV received NB UVB phototherapy in spring and treatments were given 3 times weekly with incremental dose and maintenance therapy was given twice weekly for 3–4 weeks. The mean initial, endpoint, and cumulative dose of NB UVB was 0.08, 0.33, and 6.0 J/cm², respectively. Patients totally received 27 times of treatments in average. 87.5% of previously ultraviolet B（UVB） sensitive patients and 75% of previously ultraviolet A（UVA） sensitive patients had normal or improved MED after phototherapy. The percentage of patients returned to normal UVB phototesting was higher than that of patients returned to normal UVA phototesting (68.8% vs. 37.5%). The mean 1‐week DLQI and the need for using immunosuppressive agents and antihistamines were significantly reduced after treatment (p < .01 or p < .05). In conclusion, prophylactic NB UVB phototherapy is effective and safe in treatment of CAD in Chinese patients with Fitzpatrick skin phototype IV.     

Rosacea in black South Africans with skin phototypes V and VI

Rosacea is a chronic facial dermatosis considered to affect primarily white patients with light phototype skin, and is poorly documented in black patients. The aim of this study was to document the clinical features of rosacea in patients with phototypes V and VI. An 8‐year retrospective chart review of patients with a clinical and histological diagnosis of rosacea or acne rosacea was undertaken. Of 6700 patients, 15 (0.2%) had rosacea. All were of African descent with skin phototype V or VI. Mean age was 47 years, and female : male ratio was 14 : 1. Of the 15 patients, 5 (33%) were positive for human immunodeficiency virus; 5 (33%) had used topical steroids to treat the roseacea; 6 (40%) had phototype V and presented with erythema, telangiectasia and erythematous papules, while 9 (60%) had phototype VI skin and presented with skin‐coloured papules; and 10 (67%) had histology showing granulomatous rosacea, while 5 (33%) declined a facial skin biopsy. A high index of suspicion is required to diagnose rosacea in black patients as the classic signs of erythema and telangiectasia are difficult to discern.     

Energy-based devices in the treatment of acne scars in skin of color

Background

Acne scarring is disfiguring and psychologically taxing on patients. Many energy-based modalities have emerged and been studied for the treatment of acne scarring; however, there is a paucity of these studies in skin phototypes IV–VI.

Objective

To review the medical literature and discuss the most significant studies regarding safety and efficacy of energy-based devices (ablative lasers, non-ablative lasers, and radiofrequency microneedling) in the treatment of ethnic skin (skin phototypes IV–VI).

Methods

A literature search was conducted using the PubMed database and bibliographies of relevant articles.

Results

Ablative and non-ablative lasers have proven to be effective for treatment of acne scars in ethnic skin. The risk of developing adverse effects such as post-inflammatory hyperpigmentation is contingent upon several factors including skin phototype, laser device, fluence, and moreso density settings. Non-ablative fractional lasers have been considered first line for the treatment of acne scars in skin of color due to their better safety profile; however, they are less efficacious and require more treatments compared to ablative lasers. Studies regarding efficacy and safety of radiofrequency microneedling for treatment of acne scarring in skin of color are limited, but are promising.

Conclusion

Ablative lasers, non-ablative lasers, and radiofrequency microneedling are all useful treatments for acne scarring in ethnic skin when appropriate settings are used. Further head-to-head studies are needed to evaluate their efficacy and safety in darker skin phototypes V–VI.     

Kinetics of phototoxicity in trioxysalen bath psoralen plus ultraviolet A photochemotherapy

A trioxysalen bath is a safe alternative to systemic 8-methoxypsoralen in long-term psoralen plus ultraviolet A (PUVA) treatment. The kinetics of its main side-effect, the strong phototoxicity, has not been thoroughly studied. This study determined the degree and persistence of phototoxicity after a single 10 min bath at a trioxysalen concentration of 0.33 mg/l. The buttock skin of 16 healthy volunteers was irradiated with UVA 10 min, and 1, 3, 9 and 24h after the bath. The minimal phototoxic dose (MPD) was assessed 48, 72 and 96h after the bath. In general, the 96 h reading showed the lowest values of MPD; for example, a median of 0.14 J/cm2 (95% confidence interval 0.10-0.14 J/cm2) at sites irradiated 10 min after the bath. The values increased progressively with later irradiation, and the maximum dose applied, 18.32 J/cm2, failed to produce any redness when irradiation was given 24 h after the bath. Substantial phototoxicity persists up to at least 9h after the trioxysalen bath, making it wise for patients to avoid sunshine for at least the rest of the day.     

The optimal time to determine the minimal phototoxic dose in skin photosensitized by topical 8 methoxypsoralen

BACKGROUND: We recently investigated the characteristics of psoralen plus ultraviolet (UV) A erythema in skin photosensitized by topical 8-methoxypsoralen (8-MOP) in three independent studies. OBJECTIVES: In order to determine the optimal time to read the minimal phototoxic dose (MPD) after treatment with topical 8-MOP and irradiation with UVA, we assessed the overall data. METHODS: One forearm of each subject was immersed in 8-MOP solution for 15 min and test sites on the flexor surface of the forearm were immediately exposed to a UVA dose series. Erythema was assessed visually and objectively using a reflectance instrument at 24-h intervals for 7 days. RESULTS: Results were obtained from 44 subjects (predominantly Fitzpatrick skin phototype II). A broad erythemal plateau was evident beyond 72 h and the visual MPD was significantly lower at 96, 120 and 144 h than at 72 h (P < 0.01). Only 30% of subjects were at peak erythema at the conventional MPD assessment time of 72 h. The median time to reach maximal erythema was 96 h (range 48-144). Objectively, 85% of subjects were at peak erythema at or beyond 96 h. CONCLUSIONS: We recommend that (i) the optimal time to read the topical 8-MOP MPD is 4 days after UVA exposure as readings beyond this time may be difficult to interpret because of the development of pigmentation, and (ii) 40% of the topical 8-MOP MPD should be considered for the first treatment.     

Individual photosensitivity of human skin and UVA-induced pyrimidine dimers in DNA

Delineation of the DNA-damaging properties of UVA radiation is a major issue in understanding solar carcinogenesis. Emphasis was placed in this study on the formation of cyclobutane pyrimidine dimers (CPDs), which are now well established as the most frequent UVA-induced DNA lesions in human skin. The yield of CPDs was determined by a chromatographic assay following ex vivo UVA and UVB irradiation of biopsies taken from either phototype II or IV volunteers. A clear correlation was found between the frequency of UVB-induced CPDs and both the phototype and the minimum erythemal dose (MED). Similar results were obtained for the induction of CPDs upon exposure to UVA. Moreover, an excellent correlation was observed for each donor between the yield of DNA damage induced by either UVB or UVA. These observations show that the key parameters driving UVA-induced formation of CPDs are attenuation of radiation in the skin and the number of photons reaching skin cells rather than the cellular content in photosensitizers. In addition, the results show that both MED and phototype are good predictors of the vulnerability of DNA toward UVB and UVA in the skin. This result is of importance for the identification of individuals to be extensively protected.     

乌鲁木齐地区127例志愿者紫外线最小红斑量测定

目的 测定乌鲁木齐地区志愿者长波紫外线（UVA）、中波紫外线（UVB）的最小红斑量（MED）。方法 以SUV-1000型日光紫外线模拟器为光源,测定127例志愿者UVA-MED、UVB-MED。结果 Ⅲ型皮肤48例,UVA-MED中位数为38.10 J/cm2,UVB-MED中位数为31.80 mJ/cm2;Ⅳ型皮肤79例,UVA-MED中位数为59.16 J/cm2,UVB-MED中位数为48.00 mJ/cm2。男性UVA-MED中位数为59.16 mJ/cm2,女性为41.10 J/cm2;男性UVB-MED中位数为39.60 mJ/cm2,女性为35.55 mJ/cm2。男、女性Ⅲ型与Ⅳ型皮肤UVA-MED、UVB-MED中位数差异有统计学意义,Ⅲ型皮肤均显著低于Ⅳ型皮肤。男性UVA-MED显著高于女性（P < 0.05）,UVB-MED男女之间差异无统计学意义（P > 0.05）。Ⅲ型、Ⅳ型皮肤维族与汉族比较,UVA-MED和UVB-MED差异均无统计学意义（P值均 > 0.05）,男性、女性在不同年龄组间以及不同户外停留时间组之间差异也无统计学意义（P值均 > 0.05）。通过百分位数法确定UVA-MED的正常值 > 33.38 J/cm2,UVB-MED > 27.90 mJ/cm2。结论 皮肤光反应类型是决定MED的重要因素。