Parabens are a class of widely used preservatives in cosmetic and pharmaceutical products. Chemically, they are a series of parahydroxybenzoates or esters of parahydroxybenzoic acid (also known as 4-hydroxybenzoic acid). Parabens are effective preservatives in many types of formulas. These compounds, and their salts, are used primarily for their bactericidal and fungicidal properties. They can be found in shampoos, commercial moisturizers, shaving gels, personal lubricants, topical/parenteral pharmaceuticals, spray tanning solution, makeup, and toothpaste. They are also used as food additives.
Their efficacy as preservatives, in combination with their low cost, the long history of their use, and the inefficacy of some natural alternatives like grapefruit seed extract (GSE), probably explains why parabens are so commonplace. No effective direct links between parabens and cancer have been established.
Parabens are esters of para-hydroxybenzoic acid, from which the name is derived. Common parabens include methylparaben (E number E218), ethylparaben (E214), propylparaben (E216), butylparaben and heptylparaben (E209). Less common parabens include isobutylparaben, isopropylparaben, benzylparaben and their sodium salts. The general chemical structure of a paraben is shown at the top right of this page, where R symbolizes an alkyl group such as methyl, ethyl, propyl or butyl.
All commercially used parabens are synthetically produced, although some are identical to those found in nature. They are produced by the esterification of para-hydroxybenzoic acid with the appropriate alcohol, such as methanol, ethanol, or n-propanol. para-Hydroxybenzoic acid is in turn produced industrially from a modification of the Kolbe-Schmitt reaction, using potassium phenoxide and carbon dioxide.
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Most of the available paraben toxicity data are from single-exposure studies. Further assessment of the additive and cumulative risk of multiple paraben exposure from daily use of multiple cosmetic and/or personal care products is needed. 
In individuals with normal skin, parabens are, for the most part, non-irritating and non-sensitizing. Parabens can, however, cause skin irritation and contact dermatitis and rosacea in individuals with paraben allergies, a small percentage of the general population.
Breast cancer myth
No direct evidence of a causal link between parabens and cancer has been shown. A 2005 review of the data available at that time concluded "it is biologically implausible that parabens could increase the risk of any estrogen-mediated endpoint, including effects on the male reproductive tract or breast cancer" and that "worst-case daily exposure to parabens would present substantially less risk relative to exposure to naturally occurring endocrine active chemicals in the diet such as the phytoestrogen daidzein." The American Cancer Society also concluded that there was insufficient scientific evidence to support a claim that use of cosmetics such as antiperspirants increase an individual's risk of developing breast cancer.
Animal experiments have shown that parabens have weak estrogenic activity, acting as xenoestrogens. In an in vivo study, the effect of butylparaben was determined to be approximately 100,000 times weaker than that of estradiol, and was only observed at a dose level approximately 25,000 times higher than the level typically used to preserve products. The study also found that the in vivo estrogenic activity of parabens is reduced by about three orders of magnitude compared to in vitro activity.
The estrogenic activity of parabens increases with the length of the alkyl group. It is believed that propylparaben is estrogenic to a certain degree as well, though this is expected to be less than butylparaben by virtue of its less lipophilic nature. Since it can be concluded that the estrogenic activity of butylparaben is negligible under normal use, the same should be concluded for shorter analogs.
The European Scientific Committee on Consumer Products (SCCP) stated in 2006 that the available data on parabens do not enable a decisive response to the question of whether propyl, butyl and isobutyl paraben can be safely used in cosmetic products at individual concentrations up to 0.4%, which is the allowed limit in the EU.
The above-mentioned studies have sparked scientific debate that in turn led to popular controversy, largely propagated by mass e-mail. Darbre's paper led to further discussion over possible carcinogenicity and estrogenic effects being expressed over the continued use of parabens as preservatives.
The mainstream cosmetic industry believes that parabens, like most cosmetic ingredients, are safe based on their long term use and safety record and recent scientific studies. Public interest organizations which raise awareness about cosmetic ingredients believe that further research is necessary to determine the safety of parabens, under the precautionary principle. The concerns about endocrine disruptors have led consumers and companies to search for paraben-free alternatives. Grapefruit seed extract is promoted as a natural preservative, but in a study, five out of six commercial products tested were found to contain artificial preservatives such as methylparaben and benzethonium chloride. A common alternative has been phenoxyethanol, however this has its own risks and led to an FDA warning on inclusion in nipple creams.
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