UVB-induced erythema, delayed tanning, and UVA-induced immediate tanning in Japanese skin

UVB-induced erythema, delayed tanning (DT), and UVA-induced immediate tanning (IT) in Japanese were investigated on the skin of the backs of 65 healthy subjects. The subjects were classified according to Japanese skin type (JST) based on personal history of sun-reactivity. Skin color was determined by skin reflectance using a Value Reflex Meter. With monochromatic UVR at wavelengths of 290 and 305 nm, minimal erythema dose (MED) and minimal melanogenic dose (MMD) were recorded at 24 h and 7 d after irradiation. Fading response of DT after the sunlamp-irradiation was measured by skin reflectance. Minimal IT dose (MITD) was observed immediately after irradiation with monochromatic UVR at wavelengths of 320, 340, 360, and 400 nm. The MED was exactly correlated with JST. The MED and the MMD increased with increasing JST, and with decreasing skin reflectance. The MMD was greater than the corresponding MED for individuals of all JST classes. The MITD was correlated with neither JST nor skin color. The action spectrum for IT showed a maximum at the wavelength of 320 nm and decreased gradually towards 400 nm.