BERKELEY, Calif., Oct. 27 (UPI) -- Parabens, a type of preservative used in personal care products such as shampoos, cosmetics and sunscreens, may cause cancer at lower levels than researchers previously thought.
Parabens activate the same estrogen receptors as the natural hormone estradiol and promote the growth of cancer cells.
Based on a study conducted at the University of California Berkeley, researchers said not only have previous tests potentially missed the "real world" effects of parabens by only considering them in isolation, rather than factoring in interaction with other molecules in cells.
Researchers said the study may indicate studies with other chemicals that mimic or interact with estrogen did not consider the environment outside a lab dish.
"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 Dr. Dale Leitman, a gynecologist and molecular biologist at the University of California Berkeley, in a press release. "But this might not be true when parabens are combined with other agents that regulate cell growth."
To measure how parabens interact with breast cancer cells in real life, researchers introduced the preservative to cells expressing two types of receptors, one for estrogen and the other for human epidermal growth factor receptor 2, or HER2.
Using a growth factor made in breast cells called heregulin, the researchers activated HER2 receptors in the cancer cells and exposed them to parabens -- which triggered estrogen receptors to turn genes on stimulating the growth of the tumor.
Parabens promoted cancer cell growth at concentrations 100 times lower in cells with heregulin than without. Researchers said the result suggests not only that parabens are more dangerous than previously thought, but that other chemicals should be tested at lower levels with the molecules they interact with in the body.
"While this study focused on parabens, it's also possible that the potency of other estrogen mimics have been underestimated by current testing approaches," said Chris Vulpe, a toxicologist at the Center for Environmental and Human Toxicology at the University of Florida, in a press release.
The study is published in Environmental Health Perspectives.