Independent studies have shown that commercial preparations contain the compound benzalkonium chloride, which is a synthetic antimicrobial commonly used in disinfectants and cleaning products, the related compound benzethonium chloride, the antibiotic triclosan, or the preservative methylparaben. Some samples were shown to contain up to 22% benzalkonium chloride by weight, despite the known allergenicity and toxicity of the compound at higher doses. These chemicals were not present in grapefruit seed extracts prepared in the laboratory, and GSE preparations without the contaminants were found to possess no detectable antimicrobial effect. Although citrus seed extract is sold in health food markets, there is no good evidence for any natural antimicrobial activity.
A study that examined the antiviral properties of GSE found that GSE had no efficacy as a disinfectant for feline calicivirus and feline parvovirus. Grapefruit seed extract has been advocated to be a powerful antimicrobial with proven activity against bacteria and fungi. However, independent studies have shown the efficacy of grapefruit seed extract as an antimicrobial is not demonstrated. Although citrus seed extract is claimed to be a highly effective plant-based preservative by some natural personal care manufacturers, studies asserted that the universal antimicrobial benefits associated with GSE are merely from the presence of synthetic preservatives. Natural GSE has no antimicrobial properties. Newer studies found many commercial grapefruit seed extracts contaminated with synthetic preservatives. In a 2007 study the main synthetic antimicrobial agent identified in commercial GSE samples was benzethonium chloride. In a 2008 study synthetic disinfectants such as benzethonium or benzalkonium chloride were identified in most of the commercial GSE products. In a 2008 study suspected counterfeit products were determined to contain benzethonium chloride in grapefruit seed extract samples.
Many people choose to continue to believe that GSE is a natural fungicide. It is a human trait to believe what we want to believe, even in the face of overwhelming contrary evidence. Of course the companies selling GSE insist their product is all natural, and effective.
That said, I may well take one of these 'GSE' products containing benzethonium chloride because they are very effective antimicrobials, and I think they are relatively safe if you don't increase beyond the recommended dose. But don't kid yourself that they are natural. But what is natural about eating grapefruit seeds anyway? There are lots of 'natural' things that are poisonous, and many artificial compounds that are perfectly safe. I don't think GSE is perfectly safe, but Candida isn't safe either. It is a judgement call whether the cure is worse than the disease. Like I said, I think GSE is okay as long as you don't go overboard, and perhaps don't take it forever. It will kill some of your good bacteria along with all the bad stuff. But maybe you don't have much good bacteria left anyway. View GSE as a disinfectant. It kills most everything.