Abstract: 【Abstract】 It has been speculated that dry skin results from dysfunction of epidermal permeability barrier. But so far, there is no sufficient evidence to support this speculation. In fact, dry skin indicates low levels of stratum corneum hydration. Stratum corneum hydration levels are primarily determined by the content of natural moisturizers in the skin, while epidermal permeability barrier is mainly regulated by intercellular lipids and structural proteins in the stratum corneum. If dry skin is due to a defective permeability barrier, stratum corneum hydration levels should be inversely correlated with transepidermal water loss （TEWL）, an indicator of epidermal permeability barrier function. But no negative correlation has been demonstrated between stratum corneum hydration levels and TEWL in either normal human skin, ichthyoses lesions of patients, or sebaceous gland-deficient mice in a number of studies. In contrast, a positive correlation between stratum corneum hydration levels and TEWL was observed in normal human skin. Taken together, a line of evidence suggests that dry skin unlikely indicates epidermal permeability barrier dysfunction.

Key words: Stratum corneum hydration, Epidermal permeability barrier, Transepidermal water loss, Dry skin