Parabens are preservatives widely used in personal care products, cosmetics, packaged food, and drugs to extend shelf life by preventing microbial and fungal contamination. Parabens are suspected of contributing to breast cancer risk, mainly because they have been shown to be endocrine disruptors. However, the U.S. Food and Drug Administration has determined that consumers need not be concerned about the use of cosmetics containing parabens. In addition, affected industry groups have vigorously defended the use of parabens in their products, for example, by making the claim that parabens are 10,000 to 100,000 times less active than phytoestrogens consumed in plant foods or estrogens produced in the human body. Now a new study has reported that paraben levels in breast tissue are often high enough to stimulate breast cancer cell proliferation.

Parabens are endocrine disruptors with estrogenic properties

Parabens, which are alkyl esters of p-hydroxybenzoic acid, are endocrine disruptors: chemicals that interfere with hormone systems in the body. When an endocrine disruptor is similar to a natural hormone, it can cause the body to respond as though more of the hormone were present. Other endocrine disruptors block the effects of certain hormones by interfering with their ability to interact with hormone receptors. Still others stimulate or inhibit the endocrine system directly, resulting in overproduction or underproduction of hormones. Most endocrine disruptors suspected of causing breast cancer, including parabens, have estrogenic properties in other words, they mimic estrogen. Parabens also possess androgenic properties, which means that they could interfere with male reproductive functions. The most common parabens used in consumer products are methylparaben, ethylparaben, propylparaben, butylparaben and isobutylparaben.

Parabens are suspected of helping initiate breast cancer development

Parabens are absorbed into circulation through the skin. In other words, parabens can penetrate human skin intact and be absorbed systemically. Parabens were found in 99% of breast tissue samples of breast cancer patients in one study. Another study demonstrated that parabens at concentrations found in breast cancer patients can initiate cancer development in the laboratory.

Paraben levels in breast tissue can be high enough to stimulate proliferation

The study referenced at the beginning of this news story was designed to investigate the extent to which proliferation of hormone receptor positive (ER+/PR+) breast cancer cells is influenced by exposure to five parabens (n-propylparaben, methylparaben, n-butylparaben, ethylparaben, and isobutylparaben). To conduct the study, the authors exposed MCF-7 human breast cancer cells to the parabens either alone or in combination at levels measured in 160 human breast tissue samples. A total of 43 (27%) of the 160 breast tissue samples contained at least one paraben at a concentration greater than its lowest-observed-effect concentration (LOEC), and 64 (40%) of the samples had paraben concentrations greater than no-observed-effect concentrations (NOEC).

Total paraben concentrations at or above the median levels measured in the breast tissues were found to stimulate proliferation of the MCF-7 breast cancer cells. When 22 tissue samples taken from ER+/PR+ breast tumors were considered, 12 were found to incorporate sufficient concentrations of one or more paraben to increase proliferation of MCF-7 cells. The authors conclude that the results demonstrate that parabens, either alone or in combination, are present in human breast tissue at concentrations sufficient to promote the proliferation of MCF-7 cells. The authors note that the functional consequences of paraben in human breast tissue should be evaluated on the basis of all five parabens and not single parabens individually.