Parabens are a group of chemicals widely used as preservatives in the cosmetic and pharmaceutical industries. Parabens are effective preservatives in many types of formulas. These compounds, and their salts, are used primarily for their bacteriocidal and fungicidal properties. They can be found in shampoos, commercial moisturizers, shaving gels, personal lubricants, topical/parenteral pharmaceuticals, spray tanning solution and toothpaste. They are also used as food additives.

Their efficacy as preservatives, in combination with their low cost, their long history of safe use and the unproven efficacy of natural ingredients like grapefruit seed extract (GSE), probably explains why parabens are so commonplace. They are becoming increasingly controversial, however, and some organizations which adhere to the precautionary principle object to their everyday use.

Chemistry

Parabens are esters of para-hydroxybenzoic acid, from which the name is derived. Common parabens include methylparaben (E number E218), ethylparaben (E214), propylparaben (E216) and butylparaben. Less common parabens include isobutylparaben, isopropylparaben, benzylparaben and their sodium salts. The general chemical structure of a paraben is shown at top right, where R symbolizes an alkyl group such as methyl, ethyl, propyl or butyl.

Occurrence

Molecular biologist Philippa Darbre, at the University of Reading, says that the ester-bearing form of parabens found in the tumours indicates it came from something applied to the skin, such as an underarm deodorant, cream or body spray. . Some parabens are found naturally in plant sources. For example, methylparaben is found in blueberries, where it acts as an antimicrobial agent.However,when parabens are eaten, they are metabolised and lose the ester group, making them less strongly estrogen-mimicking.

Synthesis

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. para-Hydroxybenzoic acid is in turn produced industrially from a modification of the Kolbe-Schmitt reaction, using potassium phenoxide and carbon dioxide.

Toxicology

Parabens are considered to be safe because of their low toxicity profile and their long history of safe use; however, a few recent studies have begun to challenge this view. Studies on the acute, subchronic, and chronic effects in rodents indicate that parabens are practically non-toxic.Soni, M. G.; Carabin, I. G.; Burdock, G. A. Safety assessment of esters of p-hydroxybenzoic acid (parabens). Food and Chemical Toxicology (2005), 43(7), 985-1015. doi: 10.1016/j.fct.2005.01.020 Parabens are rapidly absorbed, metabolized, and excreted. The major metabolites of parabens are p-hydroxybenzoic acid (pHBA), p-hydroxyhippuric acid (M1), p-hydroxybenzoyl glucuronide (M3), and p-carboxyphenylsulfate (M4).