Both lactic acid and lactates are very effective humectants. The main function of humectants is to keep the cosmetic product from drying out. The moisture loss figure shows that PURAC (lactic acid) and glycerin have an equal water-holding capacity, while PURASAL S (sodium lactate) has double the capacity of glycerin. (Source: A buffering humectant for cosmetics, Drug and cosmetic industry, by L.I. Osipow.)