The Right Chemistry: Preservatives are our ally in the war against fungi

Some people seem to think the risk posed by preservatives is greater than the risk posed by microbial contamination. They are wrong.

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“Let’s add some useless synthetic preservatives to our product so that we can increase our expenses, frighten our customers with chemical terms, and possibly even make them sick.”

I have never heard any food or cosmetic producer utter such a statement. Far from being useless, preservatives help us fight a war we are constantly waging. That war is against molds, fungi and bacteria, all of which can contaminate our food and cosmetics. These “natural” microbes can make us sick. Why, then, do some consumers seek out products that claim “no preservatives added?” The only possible answer is that they think the risk posed by preservatives is greater than the risk posed by microbial contamination. They are wrong. 

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Let’s take a look at one of the most maligned classes of preservatives, the parabens. These compounds, first introduced in the 1920s, are all derivatives of parahydroxy benzoic acid and are effective against molds, yeasts and many bacteria even at very low concentrations. They have low allergenicity and find particular use in cosmetics — which, due to their moisture and fat content, coupled with storage at room temperature, present a particularly hospitable environment for microbial growth.

Not all microbes are dangerous, but some are. Cosmetics can pick up microbes during manufacture or from consumers who repeatedly dip their fingers into a product they apply to their skin. That process can introduce skin microbes that then multiply in the friendly, moist environment and present a risk of infection with a subsequent application. 

Parabens were cruising along nicely until a 1998 paper published in Toxicology and Applied Pharmacology reported that they can bind to estrogen receptors on cells. This raised eyebrows because hormones like estrogen regulate many body functions and can cause problems if levels stray from the normal range. Indeed, irregularities in the development of the uterus were observed in rats exposed to parabens. Another concern was that some breast cancers are “estrogen receptor positive,” meaning that their growth can be stimulated by exposure to estrogen, or possibly by compounds like parabens that bind to estrogen receptors. 

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Often left out of the discussion is that the potency of parabens to bind to receptors in the rat uterus was 100,000 times less than that of estradiol produced naturally in the body. Furthermore, we live in a world that is replete with “phytoestrogens,” compounds found in plants that have estrogenic activity. In this category are isoflavones in soy, lignans in flax, resveratrol in red wine and coumestrol in spinach and alfalfa sprouts. Phytoestrogens, albeit in small amounts, can be detected in virtually all fruits, vegetables and legumes.  

In 2002, the pot was further stirred when Japanese researcher Shinshi Oishi published a study that documented decreased sperm production and decreased testosterone levels in male rats fed propylparaben at doses that approximated the acceptable daily intake for humans. Almost all criticism leveled at parabens since that time — and there has been plenty of it — references this study as a major reason to avoid parabens. That’s despite the publication in 2013 of a study by French researchers using superior methodology, more rats and higher doses of parabens that failed to replicate Oishi’s results. There were no effects on reproductive function.

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While parabens’ effects on the rat uterus and possible interference with sperm production were of interest to researchers, it was a 2004 study by University of Reading’s Dr. Philippa Darbre that ignited the firestorm that swept through the media and brought parabens to the attention of the public. She examined tissue that had been removed from breast tumours in a small group of 20 women and detected trace amounts of parabens. She did not claim that the chemicals caused the disease, but pointed out that parabens are used as preservatives in a range of cosmetics applied to the underarm and breast area and that “it had been suggested that regular application of such estrogenic chemicals could influence breast cancer development.”

Suggestion is not the same as demonstration. More significantly, Darbre did not test healthy women to see if they also had these compounds in their breast tissue. Nevertheless, in the eyes of the media, the story became “antiperspirants can cause breast cancer.” Never mind that none of the major antiperspirants were preserved with parabens. 

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Darbre’s subsequent experiments revealed that just about everyone has some parabens in their tissues because of the widespread use of preservatives in various products. While she has not absolved parabens of all blame, Darbre has said there are hundreds of estrogenic chemicals in the environment, both natural and synthetic, so that singling out of one set as a guilty party for affecting human health is unrealistic. In spite of its methodological flaws, Darbre’s paper has been frequently referenced with allusions to a cause-and-effect relationship between parabens and breast cancer, one that it certainly did not establish.  

No study has provided any evidence that parabens cause cancer. The International Agency for Research on Cancer (IARC), not known for sweeping any hint of carcinogenicity under the carpet, does not even list parabens as a “possible human carcinogen,” a group in which it lists 200 substances.

Nevertheless, the “no parabens” claim still attracts consumers. Are they putting themselves at risk of infection? No. Such products contain other preservatives, such as DMDM hydantoin, quaternium 15, phenoxyethanol or imidazolidinyl urea. These have also attracted the ire of some consumer advocacy groups despite numerous studies attesting to their low risk and significant benefit. Then there are preservatives like grapefruit seed extract or tea tree oil that are hyped as being “natural” but have questionable efficacy.

Even parabens could be called “natural,” since they can be found in tiny amounts in blueberries, carrots and onions. Of course, the safety or efficacy of a chemical does not depend on whether it was made by a chemist in a lab or Mother Nature in a bush. 

When it comes to preservatives, I’ll take them over microbes. 

Joe Schwarcz ([email protected]) is director of McGill University’s Office for Science & Society (mcgill.ca/oss). He hosts The Dr. Joe Show on CJAD Radio 800 AM every Sunday from 3 to 4 p.m.

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