740 Time course measurements of ultraviolet-induced skin biophysical properties

Abstract

Ultraviolet (UV) irradiation induces acute responses of sunburn and tanning, as well as long-term damages such as photocarcinogenesis and photoaging. Erythema and pigmentation are known as the most prominent acute UV responses, however, comprehensive skin biophysical changes after UV irradiation have rarely been studied. The aim of this study was to investigate dose-dependent acute effects of UV irradiation by time course changes of skin biophysical properties. 13 healthy women, with Fitzpatrick’s skin type II or III, were participated. UV doses of 0.75 (suberythemogenic dose), 1, 2 (high dose) Minimal Erythema Dose (MED) were irradiated on their back using a solar simulator, based on the preliminary determined MED. Quantitative skin biophysical properties, including melanin, erythema, transepidermal water loss, hydration, skin color and blood flow were evaluated at every 4 hours until 28 hours after irradiation. As a result, they represented different patterns with critical point of change and restoration during 28 hours. Melanin, erythema, a∗ and skin blood flow significantly increased, whereas skin barrier function, hydration, L∗ and b∗ significantly decreased when compared to non-irradiation site. Several parameters showed the lower threshold doses than visual assessment of minimal erythema formation. Regarding UV dose, the extent of change increased as the irradiation dose increased. Also, most skin parameters changed even in suberythemogenic dose. In conclusion, we found out the dose-dependent change of skin biophysical properties after acute UV irradiation with time. It is meaningful as comprehensive skin biophysical changes of short-term photodamage were identified, and they could be adopted as new quantitative parameters for objective measurement of UV protection by sunscreens. We also suggest the development of skincare products that help skin barrier function recovery after UV exposure. Furthermore, based on the results of suberythemogenic dose reflecting non-extreme UV exposure in real life, it is concluded that efficient daily UV protection is essential.