Shampoo ingredient can increase breast cancer risk

Even at low levels, a class of preservatives widely-used in consumer products like shampoos, cosmetics, body lotions, and sunscreens can contribute to development of breast cancer, suggests new research.

The estrogen-mimicking chemicals called parabens also have implications for other diseases that are influenced by estrogens, the study noted.

These chemicals are considered estrogenic because they activate the same estrogen receptor as the natural hormone estradiol.

Studies have linked exposure to estradiol and related estrogens with an increased risk of breast cancer, as well as reproductive problems.

As a result, the use of parabens in consumer products increasingly has become a public health concern.

"Although parabens are known to mimic the growth effects of estrogens on breast cancer cells, some consider their effect too weak to cause harm," said lead investigator Dale Leitman, a gynecologist and molecular biologist at University California, Berkeley in the US.

"But this might not be true when parabens are combined with other agents that regulate cell growth," Leitman noted.

However, existing chemical safety tests, which measure the effects of chemicals on human cells, look only at parabens in isolation and fail to take into account that parabens could interact with other types of signaling molecules in the cells to increase breast cancer risk.

To better reflect what goes on in real life, the researchers looked at breast cancer cells expressing two types of receptors: estrogen receptors and HER2, or human epidermal growth factor receptor 2.

The study demonstrated that parabens may be more potent at lower doses than previous studies have suggested, which may spur scientists and regulators to rethink the potential impacts of parabens on the development of breast cancer.

The findings were published online in the journal Environmental Health Perspectives.