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, cleansing gels, personal lubricants,
topical/parenteral pharmaceuticals 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.
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
Some parabens are found naturally in plant sources such as
methylparaben from the fruit of the blueberry shrub, where it acts as an antimicrobial agent.
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 used to be considered unconditionally 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.
The US Environmental Protection Agency (EPA) in their report "Pharmaceuticals and Personal Care
Products in the Environment: Agents of Subtle Change?" reported that the chemical preservatives called parabens—methyl,
propyl, butyl and ethyl (alkyl-p-hydroxybenzoates)—displayed estrogenic activity in several tests.
This
means that these chemicals mimic the body´s own hormones and can have endocrine-disrupting action when they are rubbed
into one's body or washed down the drain into our drinking water.
These disruptors interfere with the body´s
endocrine system: the hypothalamus, the ovaries, the thyroid—virtually every system in your body.
The
EPA also stated that "continual introduction of these benzoates (parabens) into sewage treatment systems and directly
to recreational waters from the skin leads to the question of risk to aquatic organisms."
Scientists
in Europe found other endocrine-disrupting body care chemicals in the bodies of fish that humans are eating, and in human
breast milk.
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).
Allergic reactions
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 in individuals with paraben allergies, a small percentage of the general population.
Breast cancer
One controversial scientific study
reports that parabens were found in samples of breast tumors. The validity of the conclusions of this study have been debated
in the scientific literature.
Nevertheless, this study has fueled the belief that parabens in underarm deodorants
or other cosmetics migrated into the breast tissue and contributed to the development of the tumors.
However,
no causal link with cancer has ever been proven and so far there is no scientific evidence to support any link with any form
of cancer.
A recent review of the available data has 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 "that worst-case daily exposure to parabens would present substantially less risk relative to exposure
to naturally occurring endocrine active chemicals (EACs) in the diet such as the phytoestrogen daidzein."
In addition, the American Cancer Society has concluded that there is no good scientific evidence to support a claim that
use of cosmetics such as antiperspirants increase an individual's risk of developing breast cancer.
Estrogenic activity
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 estradiol, although this effect was only
observed when employing a dose level which was 25,000 times higher than is actually used to preserve products.
As the estrogenic effect is dose-related, it may be calculated that the estrogenic effect at normal use concentrations of
butylparaben is 100,000 x 25,000, i.e. 2,500,000,000 times weaker than estradiol.
In the same study it was
shown that the in vivo estrogenic activity of parabens is reduced by about three orders of magnitude compared to
in vitro activity probably through the rapid metabolism of the parabens to the non-estrogenic metabolites.
In vivo data are accepted as being more relevant than in vitro data.
The estrogenic
activity of parabens increase 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.
Some estrogens are known to drive the growth of tumors; however
the estrogenic activity and mutagenic activity of estrogens are not the same with the latter dependent on free radical chemistry
and not estrogen receptor activity.
Nonetheless, this study has elicited some concern about the use of butylparaben,
and to a lesser extent other parabens as well, in cosmetics and antiperspirants.
However, there is no evidence
that any cosmetics containing parabens pose a health risk, because of the low doses involved and the fact that parabens are
unlikely to penetrate into the tissue, remain intact, and to accumulate there.
Nevertheless, the European
Scienticic Committee on Comsumer 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.
Paraben controversy
The above mentioned studies have resulted in scientific
debate that in turn led to popular controversy largely propagated by mass e-mail. The controversy has led to some concerns
(both over its possible carcinogenicity, as well as its estrogenic effect) being expressed over the continued use of parabens
as preservatives, although the scientific community has found no correlation with cancer and mostly agree that any causation
is improbable. There has been consensus that any estrogenic effect caused by the doses of parabens received from consumer
products are insignificant compared to natural estrogens and other xenoestrogens.
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 (see also precautionary principle).
The concerns have led to a significant minority shift from their usage by natural personal care companies seeking
alternatives.
