Associations between sun exposure, skin pH, and epidermal permeability in pregnancy: A longitudinal observational study

Little is known about how sun exposure may affect the maternal skin barrier during pregnancy when many hormonal and physiological changes occur. In this longitudinal observational study, 50 pregnant women were recruited at 18-24 weeks' gestation, 25 in summer-autumn, and 25 in winter-spring. At three time points in pregnancy at 18-24, 28-30, and 36-38 weeks' gestation, participants completed a validated sun exposure questionnaire and had skin permeability and surface pH measured on the volar forearm. We identified an association between increased sun exposure and increased skin permeability at 18-24 weeks' gestation (β = 0.85, p = 0.01). Lower transepidermal water loss (decreased skin permeability), mean = 12.1 (SD = 5.1) at 28-30 weeks' gestation was observed, compared to mean = 12.6 (SD = 4.0) at 18-24 weeks' and mean = 13.7 (SD = 8.5) at 36-38 weeks' gestation (n = 27, β = -1.83, p = 0.007). Higher skin pH readings, mean = 5.80 (SD = 0.58) were found at 28-30 weeks' gestation, compared to mean = 5.25 (SD = 0.62) at 18-24 weeks' and mean = 5.47 (SD = 0.57) at 36-38 weeks' gestation (n = 27, β = 0.40, p = 0.004). These gestational fluctuations remained after adjusting for Fitzpatrick skin type, season, and sun exposure. We observed gestational fluctuations in both skin permeability and skin pH, with 28-30 weeks' gestation being a significant point of difference compared to mid- and late-pregnancy periods.