Sold as a natural antimicrobial, but lab tests found the antimicrobial power of commercial extracts came from synthetic preservatives mixed in, not the grapefruit.
Grapefruit seed extract is marketed as a natural preservative and germ-fighter in toothpastes and skin products. Independent laboratory analyses of commercial extracts repeatedly found synthetic antimicrobials (benzethonium chloride, sometimes triclosan or methylparaben) at up to about 22%.
When researchers tested an uncontaminated commercial extract, and extracts they made themselves from grapefruit seed and pulp, they found no antimicrobial activity.
No clinical evidence supports an oral-health benefit. Laboratory studies indicate that genuine grapefruit seed extract has little or no antimicrobial effect and that commercial extracts' activity came from undeclared synthetic preservatives. Supply quality today may differ, but the burden of proof is on the product.
Five of six commercial grapefruit seed extracts killed a broad range of microbes, and every active one contained the synthetic preservative benzethonium chloride (some also triclosan and methylparaben). The one clean extract, and home-made extracts, had no antimicrobial activity.
Commercial products labelled grapefruit seed extract contained benzethonium chloride at 0.29-21.84%, and two contained triclosan.