Water and ion distribution profiles in human skin.

Bulk sample x-ray microanalysis (XRMA) of human gluteal skin was performed to provide data on water and ion profiles over the epidermal cross section. All samples were analyzed both in the frozen hydrated state and in the frozen dried state. This allows, for the first time, a quantitative determination of the local water content in different strata of the skin. A steep water gradient was found in the stratum corneum towards the stratum granulosum, while the water content was constant in all deeper layers of the skin, including the papillary dermis. Previously demonstrated distributions over the epidermis of the monovalent ions sodium (Na), potassium (K) and chlorine (Cl) given in concentrations per unit dry weight were confirmed, as were the distributions of phosphorus (P) and sulfur (S). Combining the water and ion distributions, our data indicate the major monovalent ions Na, K and Cl to be in equilibrium between the stratum corneum and the dermis if the assumption is that all monovalent ions are in solution and that all the water of the tissue is available as solvent for the ions. This result does not disprove the existence of an ion transport gradient in the epidermis but sets significant bounds to it.