Glycerin or glycerol is a normal component of human tissues. Involved in lipid and galactose synthesis which is metabolized to glucose or glycogen.It is found naturally in breast milk, with a highest concentration in colostrum. When it is used rectally as a laxative, has little or no absorption. It has been used in preterm infants. The oral or intravenous administration is rarely used (extracellular edema, intracranial hypertension, diagnosis of Meniere's disease). A short half-life span makes it compatible with breastfeeding in these rare cases.It also compatible with intraocular administration. It has been used in creams and gels to treat pain and cracks of nipple during lactation without clear results on effectiveness. In those cases it should be cleaned thoroughly with water before the next breast suckling to prevent it could be swallowed by the infant, since a high intestinal absorption may induce an increased plasma osmolality that can result in dehydration of the infant.