Water loss through the lip, nail, eyelid skin, scalp skin and axillary skin measured with a closed-chamber evaporation principle

Sir, Measurement of transepidermal water loss (TEWL) is a well‐established tool to assess epidermal barrier function.1 There is an abundance of TEWL data for human forearm skin, but data are limited on the water evaporation rates through the lip, nail, eyelid skin, scalp skin and axillary skin. A literature survey demonstrated no data on water loss through the lip. A few studies are available on water loss through the nail (transonychial water loss, TOWL) in vivo.2–4 These show that TOWL values decrease with age2 and that patients with eczema, psoriasis and onychomycosis have significantly lowered TOWL values compared with healthy subjects.3 One investigation was available on the evaporation rate through each of eyelid skin5 and scalp skin.6 The main problem with the scalp skin is the presence of hairs which prevent an adequate contact between the probe of the evaporimeter and the measurement site. TEWL values at the axillary skin are high and are of the same order as those at palms and soles.7 The high evaporation rates are naturally dependent on the number and capacity of sweat glands.