Redefining moisturiser

Scientists in Sweden have probed the outermost layer of skin to gain molecular insights into how naturally occurring molecules in this layer protect it from drying out.

Healthy skin with a normal degree of hydration is soft and pliable. This is not the case for dry skin, which is brittle and easily cracks. To treat dry skin it is common to apply a cosmetic containing a humectant  ?  a type of "moisturiser" – like glycerol or urea. These substances are also components of natural moisturising factor (NMF), a group of molecules naturally present in the skin barrier. The beneficial function of these compounds is often claimed to be their capacity for increasing skin hydration, although the underlying mechanisms are generally described with a rather weak molecular basis.

Sebastian Björklund and his colleagues at Lund University wanted to discover if the increased pliability and softness of dry skin treated with these compounds was due to them promoting the uptake of more water, or if there were other mechanisms to explain this. They found that molecules from the NMF increase the mobility of proteins and lipids in the stratum corneum - the outermost layer of the skin.

Using these findings to build on previous work, the team concluded that NMF compounds substitute for water in dry conditions but do not work by increasing water content. ‘Based on this, we can state that the term “moisturiser” is misleading for the types of molecules that are commonly used in skin formulations,’ Björklund says.

‘The ability of the stratum corneum to maintain the body’s moisture balance while being only half the thickness of a sheet of photocopy paper is one of the wonders of the natural world. It’s a shame that familiarity with it blinds us to how remarkable it is,’ comments Colin Sanders, founder of Colin's Cosmetic Consultancy, in the UK. ‘Cosmetic scientists have long known that glycerol and urea both have the ability to restore moisture to dry skin. But exactly how they do this is a matter of speculation. By bringing to bear the use of NMR techniques, Björklund and his colleagues have shown that these agents affect the mobility of the lipids in the skin. This may well turn out to be a key clue in how they work, which might help to produce new and better moisturisers,’ he adds.