On the Variation of Water Diffusion Coefficient in Stratum Corneum With Water Content

Abstract

Water permeability and transient water sorption data in human and porcine stratum corneum (SC) are analyzed in conjunction with equilibrium water sorption data and a dynamic skin swelling model to develop a quantitative model for water diffusivity in the SC as a function of its water content. The recommended function (model 1) is phenomenological and treats the SC as a uniform, swellable slab. This approach yields satisfactory agreement with experimental data over a wide range of RH and associated equilibrium SC water content, Cw. It is supported by two alternative approaches. Model 2 considers the SC to be a multilaminate membrane consisting of alternating lipid and protein layers. Diffusivity in the protein phase is estimated from water diffusivity in other keratinized tissues, whereas diffusivity in the lipid phase is assumed to be linearly related to the swelling strain on intercellular lipids. Model 3 uses an analysis previously suggested by Stockdale to rationalize transepidermal water loss data in humans over a wide range of relative humidity. All models yield similar results for 0.20 ≤ Cw ≤ 0.78 g/cm(3), the usual range of SC water content in vivo.

In vivo confirmation of hydration-induced changes in human-skin thickness, roughness and interaction with the environment

“…This could indicate at least two different water diffusion mechanisms as expressed in the literature by multilayer or multicompartment skin models and the finding of true formation of water pools within the SC. [50][51][52] This observation is consistent with a statement by Loth that the transport of water within the SC disjunctum takes place through spreading into the intercellular space due to the capillary forces, whereas the much slower and less straightforward water transport within the SC conjunctum is based only upon diffusion. 18,[53][54][55] This also explains the observation that the closer to the surface of the skin, the faster and more significant is the water uptake as well as the fact that even a short exposure to water (2 min) caused appreciable changes in the SSC.…”

“…16,35 Water diffusion requires space and therefore leads to physical expansion, i.e., swelling. 51,52 For all investigated parameters, an increase in relative humidity had a minor influence on the skin compared to the direct contact with water. Skin hydrated through the exposure to humid conditions followed the same tendencies as the skin hydrated through the direct exposure to water, but to a much lesser extent.…”

Water adsorption with relative humidity changes for keratin and collagen as studied by infrared (IR) micro‐spectroscopy

“…Secondly, as is indicated by some hydration experiments of human skins measured by confocal Raman microscopy, water contents at the SC surface increase by keeping the constant deeper water contents . Moreover, water contents at the SC surface are considered to affect skin health and diffusion of chemical components including water itself . Therefore, transport properties of SC should be evaluated in relation to the surface water contents.…”

“…Water contents at the stratum corneum (SC) of human skins are considered to affect skin health and penetration of several chemical components . Water contents of human SC have been evaluated mostly by relative values using electrical methods, which correspond to water contents throughout the whole SC layers.…”

A new topical panthenol-containing emollient: skin-moisturizing effect following single and prolonged usage in healthy adults, and tolerability in healthy infants

“…In a blinded randomized 3-week study in healthy subjects, the application of a vitamin B 3 (nicotinamide)-containing moisturizer to the volar forearm, increased SC thickness, water gradients and hydration as measured by confocal Raman spectroscopy (13). The SC swells as the water content increases leading to SC thickening (32). An increase in SC thickness upon topical application has also been reported for a lipophilic niacin derivative (33).…”