Parabens are preservatives widely used in personal care products, cosmetics, food and drugs to prevent microbial and fungal contamination. Parabens have been suspected of contributing to breast cancer risk because they are endocrine disruptors (chemicals that interfere with hormone systems in the body). Despite long-standing interest in the topic, research into the possible link between parabens and breast cancer is not far advanced and a firm link to breast cancer has not been established. Now a new study has reported that parabens at concentrations found in breast cancer patients can initiate cancer development in the laboratory.

Parabens can be absorbed through the skin

It has been demonstrated that parabens are absorbed into circulation through the skin. In other words, parabens can penetrate human skin intact and be absorbed systemically. A study of 332 healthy women reported that methyl paraben was detected in 63% of the women's blood samples, propyl paraben was found in 29%, and ethyl paraben was in found in 22%. The paraben levels were related to the women's use of skin lotions, indicating that frequent use maintains elevated levels. Parabens have also been reported to be found in human breast tissue.

Latest research finds that parabens have carcinogenic properties

The study referenced at the beginning of this news article was designed to investigate the potential carcinogenic properties of parabens. The possibility of a link between parabens and breast cancer risk has been raised, but studies have concentrated on parabens' estrogenic activity and little attention has been given to the possibility that parabens have outright carcinogenic properties.

In the study, the authors used MCF-10A immortalized but non-transformed human breast epithelial cells. MCF-10A cells, which do not have any invasive or tumor forming characteristics, are considered to be similar to normal breast cells. MCF-10A cells can be used to model the transition from normal to transformed to invasive to fully malignant breast cancer. Transformed cells give rise to solid masses when exposed to carcinogens.

Parabens were found to be capable of inducing anchorage-independent growth of MCF-10A immortalized but non-transformed cells. Such growth is closely related to transformation and a predictor of tumor growth. MCF-10A cells produced very few colonies of small size in normal culture. However, when methylparaben, propylparaben or n-butylparaben were added, a greater number of colonies per dish were produced and the average colony size increased in each case. Dose-response experiments demonstrated that very low concentrations of the parabens could increase colony numbers.

The authors then compared these very low concentrations to the paraben levels measured in a previous study in human breast tissue samples from 40 mastectomies (see the first study below). It was found that 22 of the 40 patients had at least one of the parabens in their tumors at or above these low concentrations. The authors comment that this is the first study to report that parabens can induce a transformed phenotype in human breast epithelial cells in the laboratory and that further investigation is justified into a potential link between parabens and breast cancer development.

Bottom line

A previous study found that high paraben levels were not specifically associated with estrogen receptor positive (ER+) disease, which contradicted the theory that parabens increase breast cancer risk through estrogenic actions. This study, while preliminary, could offer an explanation. In any case, it makes sense to choose paraben-free personal care products (especially lotions and creams) to be on the safe side.