"When sold in the US, the label often says Glycerin USP. USP stands for United States Pharmacopeia. The United States Pharmacopeia is an official public standards–setting authority for all prescription and over–the–counter medicines and other health care products manufactured or sold in the United States.
Food-grade Glycerin is glycerin that has been processed and packaged using equipment clean enough that the product can be safely eaten by people. If you are ingesting glycerin, this is the one to buy. But if you are using glycerin on your skin, the extra expense is not necessary."