Proc. Natl Acad. Sci. USA 113, 10275–10280 (2016)

Our skin saves us. Without it, the cells in our bodies would quickly dry out. Beyond presenting a physical barrier, mammalian skin also actively keeps the water-evaporation rate practically constant, up to a relative humidity of ∼85%. Kevin Roger and colleagues have now found that simple aqueous solutions of amphiphilic molecules — which have both hydrophilic and hydrophobic parts — mimic this sort of humidity buffering.

Using optical and infrared microscopy as well as small-angle X-ray scattering, they found that the key to the skin-like behaviour in these solutions is an air–liquid interface that reacts through self-assembly to changes in humidity. This process controls the thickness and structure of the interface — and thus its permeability — resulting in a feedback loop where stronger driving forces due to increasing gradients in relative humidity are balanced by decreasing the permeability of the interface.

A similar sort of feedback loop could be at work in the stratum corneum layer of our skin, where phase transitions in the lipid self-assembly structure have been observed. Having a fuller understanding of the underlying mechanism might lead to fresh approaches to remedy skin diseases.