Humidity transepidermal water loss

Dry, scaly skin is characterized by a decrease in the water retention capacity of the stratum corneum (SC),1 with water content diminished to less than 10%. Barrier function of the SC is usually declined, and transepidermal water loss (TEWL) is increased because of an abnormality on barrier homeostasis.2 People feel tightness of their skin, and the skin surface becomes rough, scaly, and sensitive. Hyperkeratosis, abnormal scaling, and epidermal hyperplasia are usually observed in the dry skin.2 Keratinization also shows abnormal features.2 These phenomena are commonly observed in atopic dermatitis and psoriasis.3 Dermatitis induced by environmental factors such as exposure to chemicals, low humidity, and UV radiation also shows these features. Thus, many researchers have been investigating the cause and treatment of dry skin, and there is currently great interest in adequate model systems for dry skin studies. In this chapter, I will describe several model systems of dry skin for clinical research of dermatitis associated with skin surface dryness and also mention recent studies to improve the dry skin. 

McCallion, R. and Po, A.L.W., Modelling transepidermal water loss under steady-state and non-steady-state relative humidities, Int. J. Pharm., 105, 103, 1994. 

A short-term test that measures transepidermal water loss (TEWL) is also used to measme barrier integrity and has been mentioned specifically as an acceptable method by the Emopean Union s Scientific Committee for Cosmetics and Non-Food Products (Scientific Committee, 2003). Measinement of TEWL from skin samples in diffusion cells appears to be a potentially convenient method that does not use radiolabeled material. However, some effort appears to be necessary to obtain consistent measmements, including the possible need for rooms with controlled environments for humidity and temperature (Benech-Kieffer et al., 1998). Some reports have found differences between skin permeability evaluations by tritiated water and TEWL methods (Chilcott et al., 2002). 

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