Skin pH mapping and its relationship with transepidermal water loss, hydration and disease severity in adult patients with atopic dermatitis

BACKGROUND: Defective skin's acidic mantle is a component of atopic dermatitis (AD) pathophysiology. We mapped the skin pH and determine its relationship with transepidermal water loss (TEWL), hydration and disease severity. MATERIALS AND METHODS: A cross-sectional study involving patients aged ≥18 years. Eczema Area and Severity Index (EASI) was assessed. Skin pH, TEWL and hydration were measured at 18 pre-determined sites. RESULTS: Forty-eight patients participated, 33(68.8%) females and 15(31.3%) males aged 28.46 ± 12.07 years. The overall skin pH was 5.32 ± 0.68 ranging from 5.16 ± 0.75 to 5.52 ± 0.59. The lowest pH 5.16 ± 0.75 was at anterior leg, popliteal fossae 5.18 ± 0.67, lower back 5.21 ± 0.64, forehead 5.22 ± 0.62, upper back 5.25 ± 0.65 and neck 5.26 ± 0.76. Highest pH was at the cheek 5.52 ± 0.59, anterior thigh 5.47 ± 0.68, dorsal arm 5.46 ± 0.68, volar arm 5.43 ± 0.67 and abdomen 5.39 ± 0.67. Lesional areas' pH (5.40 ± 0.13) was higher than nonlesional (5.27 ± 0.14), P = .01. pH at AD predilection sites was significantly lower non-predilection sites (5.26 ± 0.59 vs 5.34 ± 0.64). pH did not correlate with TEWL (r = .23, P = .12), EASI (r = .19, P = .20) and itch (r = .06, P = .70) but correlated with hydration r = -.33, P = .02. CONCLUSION: Skin pH was lower at AD predilection sites. There was no correlation between pH with AD severity and TEWL, pH correlated with hydration.