Preservatives and Parabens
Parabens refer to a group of esters of 4-hydroxybenzoic acid commonly used as preservatives in foods, pharmaceuticals, and cosmetics whose widespread use dates back to 1923.16 Concerns over the presence of parabens in shampoos and other cosmetics have been raised by patients for their reputed estrogenic and antiandrogenic effects and suspected involvement in carcinogenesis via endocrine modulation.16,17 In in vitro studies done on yeast assays, parabens have shown weak estrogenic activity that increases in proportion to both the length and increased branching of the alkyl side chains in the paraben’s molecular structure.18 They are 10,000-fold less potent than 17β-estradiol. In in vivo animal studies, parabens show weak estrogenic activity and are 100,000-fold less potent than 17β-estradiol.18 4-Hydroxybenzoic acid, a common metabolite, showed no estrogenic activity when tested both in vitro and in vivo.19 Some concerning research has implicated a link between parabens used in underarm cosmetics, such as deodorants and antiperspirants, and breast cancer16; however, the studies have been conflicting, and there is simply not enough data to assert that parabens cause breast cancer.
The Cosmetic Ingredient Review expert panel first reviewed parabens in 1984 and concluded that “methylparaben, ethylparaben, propylparaben, and butylparaben are safe as cosmetic ingredients in the present practices of use.”20 They extended this statement to include isopropylparaben and isobutylparaben in a later review.21 In 2005, the Scientific Committee on Consumer Products (now known as the Scientific Committee for Consumer Safety) in Europe stated that methylparaben and ethylparaben can be used at levels up to 0.4% in products.22 This decision was reached due to reports of decreased sperm counts and testosterone levels in male juvenile rats exposed to these parabens; however, these reults were not successfully replicated in larger studies.16,22 In 2010, the Scientific Committee for Consumer Safety revisited its stance on parabens, and they then revised their recommendations to say that concentrations of propylparaben and butylparaben should not exceed concentrations of 0.19%, based on “the conservative choice for the calculation of the [Margin-of-Safety] of butyl- and propylparaben.”23 However, in 2011 the use of propylparaben and butylparaben was banned in Denmark for cosmetic products used in children 3 years or younger,16 and the European Commission subsequently amended their directive in 2014, banning isopropylparaben, isobutylparaben, phenylparaben, benzylparaben, and pentylparaben due to lack of data available to evaluate the human risk of these products.24
Contrary to the trends in Europe, there currently are no regulations against the use of parabens in shampoos or other cosmetics in the United States. The American Cancer Society found that there is no evidence to suggest that the current levels of parabens in cosmetic products (eg, antiperspirants) increase one’s risk of breast cancer.25 Parabens are readily absorbed into the body both transdermally and through ingestion but also are believed to be rapidly transformed into harmless and nonspecific metabolites; they are readily metabolized by the liver and excreted in urine, and there is no measured accumulation in tissues.17
Parabens continue to be the most widely used preservatives in personal care products, usually in conjunction with other preservatives. Parabens are good biocides; short-chain esters (eg, methylparabens, ethylparabens) are effective against gram-positive bacteria and are weakly effective against gram-negative bacteria. Long-chain paraben esters (eg, propylparabens, butylparabens) are effective against mold and yeast. The addition of other preservatives creates a broad spectrum of antimicrobial defense in consumer products. Other preservatives include formaldehyde releasers or phenoxyethanol, as well as chelating agents such as EDTA, which improve the stability of these cosmetic products when exposed to air.16 Parabens are naturally occurring substances found in foods such as blueberries, barley, strawberries, yeast, olives, and grapes. As a colorless, odorless, and inexpensive substance, their use has been heavily favored in cosmetic and food products.16
