Measurement of shrinkage ability of the stratum corneum under dehydration conditions

Pliability and elasticity of stratum corneum (SC) depends on hydration. The aim of the present study was to introduce a new method for the measurement of the ability of the stratum corneum to shrink following dehydration and rehydration.

The experimental bulla roof of 6 normal volunteers, 3 men and 3 women (40-60 years old) and 2 patients suffering from x-linked ichthyosis were examined. The experimental bulla was made on the flexure surface of the left forearm after exposure to NH4 OH vapors for 15 min. The measurements were performed by the Cutech In Vivo Extensometer (Stiefel). The instrument arms were retained constant and each force applied upon them was able to recorded by graph, and that force was measured quantitatively. The bulla roof was stuck on the instrument arms, in situ.

In the laboratory environment, the adherent SC on the instrument arms was dehydrated and as a result, a shrinkage force appeared which reached a maximum (mean value=21.6 g; force per 0.6 cm(2) of SC) at 18-25 minutes. Artificial SC hydration (2 drops of water for 10 s, separately on each SC surface) showed as a result immediate disappearance of the shrinkage force which was followed by a gradual reappearance of the shrinkage force level at 8-16 min. This phenomenon had a high reproducibility. Similar phenomena were observed in the SC of the x-linked ichthyosis patients.

We considered that the shrinkage ability of the SC can be used as a marker to study SC hydration; it is also responsible for some clinical problems (chapping during winter, cracking in asteatosis, etc.) and plays an important role in desquamation of a single corneocyte or scale. Our experimental model can be used to evaluate substances or emolients'action on SC hydration.