Abstract: Objective To determine the normal range of minimal erythema dose (MED) of normal skin to ultraviolet A (UVA) and B (UVB). Methods The definition of MED is the dose of UVA required to induce a just perceptible erythema on an individual's skin 24 hours after irradiation. One hundred and eighteen subjects including healthy volunteers and patients with noninflammatory skin disorders were enrolled and studied with SUV1000 type UV simulator in March 2002. Results The average MED value for UVA was 55 J/cm² (range:18-95 J/cm²) in the males, and 40 J/cm² (range:15-100 J/cm²) in the females. The average MED value for UVB was 31 mJ/cm² (range:12-95 mJ/cm²) in the males and 29 mJ/cm² (range:8-95 mJ/cm²) in the females. The MED value for UVA in the males was significantly higher than that in the females (P<0.05). There was no difference of the MED value for UVB between male and female (P>0.05). The MED values for UVA as well as UVB in skin type Ⅲ were significantly lower than those in skin type Ⅳ (UVA-MED:P<0.05 in male, P<0.05 in female; UVB-MED:P<0.05 in male, P<0.01 in female). The correlation between the MED values and age was not found in the female. Compared with other age groups, male aged from 30 to 49 had a much lower MED value for UVB, but not for UVA. Both UVA-MED and UVB-MED of cloth-covered sites were not correlated to the duration of outdoor exposure. Conclusion It is indicated that the MED values of normal skin to UV are mainly dependent on the skin types.

Key words: Minimal erythema dose, Ultraviolet rays