Effects of particulate matter on healthy human skin: a panel study using a smartphone application measuring daily skin condition

Background: The influence of particulate matter (PM) on human health has recently attracted attention. However, most previous studies have been limited to diseased skin. Objectives: To evaluate the effects of PM on healthy skin. Methods: The study enrolled 188 healthy volunteers without any skin disease during winter and early spring. Every day for 14 days, they recorded their skin states using a smartphone application, which automatically scored facial skin condition in terms of wrinkle, brown-spot and trouble indexes based on a selfie. Subjects recorded information about their personal lifestyles such as sleeping time and outdoor activity. Air pollution and meteorological information were collected during the same period as well. We analysed the correlation between daily skin condition and environmental factors. Results: Overall, 2625 person-days were obtained for 3 months from February to April. Among the various factors analysed in this study, temperature and PM showed statistically significant relationships with the daily condition. Multivariable analysis showed a cumulative effect, as PM_2.5 from 8 to 3 days prior to when daily skin condition was checked had a negative correlation with wrinkle index (P < 0.05). Conclusions: Inadequate outdoor temperature can immediately impinge on the skin state of even healthy people. PM_2.5 may contribute to skin ageing gradually rather than immediately.