Grapefruit seed extract
However, tests on actual grapefruit (Citrus × paradisi) seed extract show zero antimicrobial or antifungal properties, while tests on commercially available GSE do show such properties. The difference? Tests on commercial GSE products show they contain benzethonium chloride and triclosan, both antimicrobial and antifungal compounds also used in deodorants, disinfectant sprays, and antiseptic hand wipes. Neither of these compounds occur naturally in grapefruit seed extract, which indicates they were either added to "all-natural" grapefruit seed extract products as preservatives, or GSE products were adulterated with those compounds to give them their claimed benefits. Benzethonium chloride and triclosan, while effective, are approved and generally regarded as safe for external use only, but specifically disapproved for internal use.
Bottom line: GSE products sold in health food stores are not "all-natural". Their apparent active ingredients aren't listed on the label. The actual amount of benzethonium chloride and triclosan they contain could vary widely, making their effectiveness for any given application unclear. Given these unknowns and the unapproved status of these two compounds for internal use, it is probably a very bad idea to take GSE products internally.
- Aspects of the antimicrobial efficacy of grapefruit seed extract and its relation to preservative substances contained, von Woedtke T, Schlüter B, Pflegel P, Lindequist U, Jülich WD, Pharmazie. 1999 Jun;54(6):452-6.
- Identification of benzethonium chloride in commercial grapefruit seed extracts, Takeoka G, Dao L, Wong RY, Lundin R, Mahoney N, J Agric Food Chem. 2001 Jul;49(7):3316-20.
- Simultaneous identification and quantification by liquid chromatography of benzethonium chloride, methyl paraben and triclosan in commercial products labeled as grapefruit seed extract, Avula B, Dentali S, Khan IA, Pharmazie. 2007 Aug;62(8):593-6.