A randomized double-blind study was designed with 65 patients in order to clarify two points: (1) does addition of a retinoid to psoralen-ultra violet A photochemotherapy (PUVA) of severe psoriasis decrease the UVA energy required to achieve remission, and (2) is there a difference between two retinoids, i.e. etretinate and acitretin. Acitretin-PUVA treatment was significantly superior to placebo-PUVA with respect to several items (decrease in lesional scores after 6 weeks of therapy, number of PUVA exposures, and total dose of UVA until remission). There were also differences between the etretinate-PUVA and placebo-PUVA groups, but only the decrease in lesional scores reached statistical significance.

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Variations in individual sunburn sensitivity have been studied using erythema as the photobiologic criterion. The minimal erythema dose (MED), the minimal dose necessary to elicit an intense erythema (MED++), and an edema (MOD), were determined by Saidman's method. The irradiation was performed with a 2,500-W xenon arc solar simulator fitted with a water filter and WG 305 Schott filter. The high correlation between MED, MED++, and MOD and the existence of saturation phenomenon confirm that determination of MED is the best photobiologic criterion. The average MED and the pathologic threshold for total light spectrum irradiation are, respectively, 889 mJ/cm2 and 347 mJ/cm2. A statistically significant variation in MED as a function of age, sex, complexion, eye color, hair color, and Fitzpatrick skin type has been established. Finally, complexion has been shown to be the best clinical criterion for the characterization of sunburn sensitivity and a new classification of the epidermis for UV therapy and artificial photoprotection is proposed.

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