Glycerol is a trihydroxy sugar alcohol that is an intermediate in carbohydrate and lipid metabolism. It is used as a solvent, emollient, pharmaceutical agent, and sweetening agent.
from MeSH
Glycerin is a Non-Standardized Chemical Allergen. The physiologic effect of glycerin is by means of Increased Histamine Release, Cell-mediated Immunity, and Increased IgG Production. The chemical classification of glycerin is Allergens and Glycerol.
FDA Pharmacology Summary from FDA Pharm Classes
Glycerin is a trihydroxyalcohol with localized osmotic diuretic and laxative effects. Glycerin elevates the blood plasma osmolality thereby extracting water from tissues into interstitial fluid and plasma. This agent also prevents water reabsorption in the proximal tubule in the kidney leading to an increase in water and sodium excretion and a reduction in blood volume. Administered rectally, glycerin exerts a hyperosmotic laxative effect by attracting water into the rectum, thereby relieving constipation. In addition, glycerin is used as a solvent, humectant and vehicle in various pharmaceutical preparations.