Transepidermal

Transepidermal is an adjective used in dermatology and skin science to describe processes or phenomena that occur across the epidermis, the outermost layer of the skin and a key component of the skin’s barrier.

The term is commonly encountered in reference to transepidermal water loss (TEWL), the passive diffusion of water from the dermis through the epidermis to the external environment. TEWL is widely used as an indicator of skin barrier integrity and health; higher TEWL indicates a compromised or disrupted barrier. Measurement is typically performed with devices such as tewameters, which assess the evaporative water loss from the skin surface under standardized conditions.

Transepidermal pathways also describe the route by which topical substances can pass through the epidermis. In pharmacology and cosmetics, transepidermal absorption refers to molecules crossing the epidermis, often toward localized effects within the skin. In some contexts this route is discussed alongside transdermal delivery, which is specifically aimed at systemic absorption. The epidermis, particularly the stratum corneum, serves as the principal barrier to such passage.

Transepidermal processes are influenced by several factors, including the integrity and hydration of the skin, age, presence of skin disease (for example, eczema or psoriasis), environmental conditions, and the physicochemical properties of the substance (notably lipophilicity and molecular size).

In summary, transepidermal describes movement across the epidermis, with TEWL as a central measurable example and broader relevance to topical absorption and barrier function.