Dry skin concerns many individuals, conferring discomfort and even impacting the lives of those severely affected. However, in most cases it can be adequately managed with current moisturizing products.
Glycerol is one humectant commonly employed due to its high hygroscopic and hyperosmotic properties. It is used in cosmetics as a moisturizer and in pharmaceutical formulations as an active compound. Being naturally present in the skin, glycerol was quickly identified for its role in skin hydration, similar to natural moisturizing factors (NMF). A byproduct of triglyceride lipolysis, it is transported from the dermis through keratinocytes by a transmembrane water/glycerol transporting protein, aquaporin 3.
Glycerol also protects skin against irritant dermatitis and accelerates the recovery of irritated skin. One in vivo study by Flurh et al. assumes that the stimulus for barrier repair occurs through water flux due to the hygroscopic properties of glycerol. Likewise, most studies about skin barrier recovery are performed with relatively high concentrations of glycerol, e.g., from 5% to 50%, often dispersed in an emulsion.
The question arises as to whether glycerol acts solely through its hygroscopic properties or implies more specific mechanisms. Indeed, diglycerol and triglycerol, with higher humectant activity, have demonstrated low improvements in skin dryness, compared with glycerol. Also, one in vivo attempt has been made to characterize the effects of low glycerol doses, e.g. from 1% up to 10%, on water transport through the skin after acute chemical irritation by sodium lauryl sulfate (SLS). The present article therefore summarizes and clarifies the benefit of glycerol on irritated skin.
Inducing and Assessing Irritation
Seven skin areas on the volar forearm of four female volunteers were delimited and treated for three hours with 200 µL of a 10% sodium lauryl sulfate (SLS) aqueous solution under occlusion with plastic closed chambers. One site was treated with 200 µL deionized water as a control site. Irritated skin areas presented as having disrupted barrier function and reduced hydration, as determined by biophysical measurements of transepidermal water loss (TEWL) and hydration.