Methyl Paraben-13C6 (Methyl 4-hydroxybenzoate-13C6) is a 13C labeled Methyl Paraben (HY-N0349)[1]. Methyl Paraben, isolated from the barks of Tsuga dumosa the methyl ester of p-hydroxybenzoic acid, is a standardized chemical allergen. Methyl Paraben is a stable, non-volatile compound used as an antimicrobial preservative in foods, agents and cosmetics. The physiologic effect of Methyl Paraben is by means of increased histamine release, and cell-mediated immunity[2].