Ultraviolet (UV) irradiation affects the function and complexion of the skin by inducing changes in physical properties through formation of erythema, proliferation of epithelial cells, DNA damage, activation or inactivation of various enzymes and proteins, and free radical formation. In this study, the authors intended to observe the overall course of changes in barrier function and reflectance of the skin induced by photodamage, and healing reaction in the course of time, and alteration of the skin complexion.
The subjects were chosen from 15 healthy Korean men 20-35 in age, that fall into the category of Fitzpatrick's skin types II, III, and IV without history of recent exposure to sunlight, photosensitivity, or having taken any drugs that induce phototoxicity or photoallergic reactions. The subjects were artificially exposed to suberythemogenic dose [0.5 minimal erythemal dose (MED), 0.75 MED], 1 MED and high dose (2.5 MED) by solar simulator, and changes in skin barrier function and skin reflectance were assessed with a Tewameter, a Corneometer, and a Colorimeter for 4 weeks.
Transepidermal water loss (TEWL) increased abruptly at Day 1 of single solar UV (SSUV) exposure, and slowly returned to the original level from Day 2/Day 3. In the case of exposure with 0.75 MED, it returned to the original level at Day 4 of exposure, and at Days 7 and 28 in the cases of 1 MED and 2.5 MED exposure, respectively. Water-holding capacity sharply declined at Day 1 of exposure, hitting the lowest point at Day 2, and then slowly recovered starting on Day 3. In the case of exposure with 0.75 MED and 1 MED, it returned to the original level at Days 7 and 28 in the case of 2.5 MED exposure. The a(*) values abruptly increased and reached the peak at Day 1 and slowly returned to the original level at Day 2, while the b(*) values slowly increased at Day 3, peaking at Day 7 and slowly returning to the original level thereafter. The L(*) values abruptly declined at Day 1, maintaining plateau through Day 7 and slowly returning to the baseline level thereafter. The individual typology angle (ITA degrees) were compatible with L(*) values change. The erythema index increased abruptly at Day 1 of SSUV exposure, peaking at Day 2 and slowly returned to the original level starting at Day 3. Melanin index slowly started to increase on Day 3 of SSUV exposure, peaking at Day 7 and gradually returned to the original level thereafter. However, L(*), a(*), b(*), erythema index, and melanin index did not return to the original level during the 28-day course of this study.
This study shows that in the skin of Korean subjects, changes in skin barrier function and delayed melanization do occur even in exposure to a suberythemogenic dose of SSUV. Also, given the fact that restoration of barrier function occurs as the process of melanization begins, melanization is considered to be a useful predictive indicator of the restoration of the skin barrier function after sunburn.