Changes in the Skin Moisture Contents, Skin Color, and Skin Protein Conformational Structures of Sprague-Dawley Rats after Ultraviolet B Irradiation

Abstract

The influence of ultraviolet B (UVB) irradiation on the skin moisture contents, skin color, and protein secondary structure in the skin of alive Sprague-Dawley (SD) rats was investigated. The UVB irradiation source emitted 725 ± 10 μW/cm² of UVB range with a peak at 302 nm during the exposure course of 6 h/day for 3 successive days. The moisture content of SD rat’s skin first decreased with the UVB irradiation, then returned to normal level on days 1 and 2, and, finally, decreased significantly with the increase of UVB irradiation on day 3. After the 6-hour irradiation on days 1 and 2, the moisture contents of the irradiated skin of SD rat returned to normal values, suggesting repairability of the irradiated skin of SD rat during the following 18 hour period without irradiation. By increasing frequency and duration of UVB irradiation, the skin color parameters exhibited a lower L* value, a greater a* value, and a higher ΔE value, indicating that the skin color darkened and reddened. The slight modification of protein secondary structure of the skin of SD rats after repeated UVB irradiation was evidenced. However, the infrared spectrum during the initial course of irradiation, from day 1 to day 3, exhibited a similar pattern. Thus, the alive SD rat’s skin was repairable during the 18-hour period without irradiation.