By Brenda Goodman, MA
WebMD Health News
Reviewed by Brunilda Nazario, MD
Oct. 27, 2015 -- A new study has found that chemicals called parabens can spur the growth of certain types of breast cancer cells. And they appear to be able to do this even in tiny amounts.
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Parabens are used in many food and personal care products. They have a chemical structure that's similar to estrogen, which means they can mimic the effects of that hormone in the body. But they seem do this weakly, and on the scale of chemical threats, researchers thought parabens were pretty low on the list of things to worry about.
New research suggests, though, that they may be more harmful than previously thought.
For the study, scientists grew breast cancer cells in a lab. They treated the cancer cells with low doses of parabens along with heregulin, a growth-promoting substance that's normally found in breast tissue. The two chemicals are known to have a more powerful effect when combined.
When the two chemicals were combined, the dose of parabens needed to stimulate growth was 100 times lower. That suggests parabens may be exerting effects at levels people are being exposed to in real life, according to study author Ruthann Rudel, who co-directs the research program for the non-profit Silent Spring Institute.
WebMD asked experts to discuss the findings.
Q: What are parabens?
They're preservatives. They prevent bacteria from growing in things like face moisturizer, which repeatedly comes into contact with germs from your hands as you scoop it out to apply it to your face. The American Chemical Society estimates that parabens are in about 85% of personal care products -- everything from shampoo to shaving cream. Researchers believe most of us get our greatest exposure from these products as they're absorbed through the skin.
Parabens can also be found in foods like baked goods, beverages, syrups, jellies, jams and preserves, in the packaging that keeps food fresh, and in drugs, according to the CDC's National Biomonitoring Program.
The most commonly used parabens are methylparaben, propylparaben, and butylparaben, according to the FDA.
Q: Who is exposed to them?
Everybody. A recent study that tested 183 adults and children in California found parabens in 70% to 100% of their urine samples -- depending on the specific paraben they were looking for.
Adults tended to have more of these chemicals in their urine than children, probably because they used about twice the number of personal care products.
The same study found that the more personal care products a person used, the higher their paraben levels. Women tend to have higher levels than men, probably because they use more.
The good news is that these chemicals are cleared from the body pretty quickly, says Claire Philippat, PhD, a post-doctoral researcher at the University of California at Davis who studies paraben exposure.
The bad news is that because they're so widely used, we always have some in our bodies.
"Even if you eliminate them quickly, you're continually exposed to them," Philippat says.
Q: Are parabens harmful?
Scientists are working hard to understand this. Parabens have a chemical structure that's similar to estrogen, and they can mimic this hormone's activity in the body. But they aren't particularly strong. They're about 10,000 to 100,000 times less potent than the natural hormone, according to the CDC.
"I would definitely say when we line up all the chemicals, they don't tend to stand out. They're fairly weak estrogen mimics. They aren't compounds that rise to the top of our concern level," says Robin Dodson, ScD, a research scientist at the Silent Spring Institute.
The new study found that in the presence of growth-promoting substances that are normally in breast tissue, parabens can promote the growth of estrogen-sensitive breast tumors even in tiny amounts -- around 5 to 10 nanograms. A nanogram is a billionth of a gram. "The question is: Would humans have those kinds of concentrations in their tissues or blood?" Rudel says.
Q: Are the levels of parabens tested in the study like the levels we're exposed to in real life?
The short answer is that we don't know. There have only been a few studies that have ever tried to measure the chemical in blood or tissues.
Two studies have found parabens in human breast tumors. But those studies have been questioned, because researchers can't rule out that the samples may have been contaminated with parabens as they were being prepared for analysis.
A large, ongoing study by the CDC is tracking Americans' exposure to many chemicals, including parabens. Based on data collected for that study, Rudel says people who get exposed to the highest levels in the U.S. have paraben concentrations in their bodies that are about at the levels used in the new study.
"But there isn't direct evidence," she says.
Q: What other limitations of the study should we know about?
The scientists tested breast cancer cells that were known to be sensitive to (or fueled by) hormones.
"Those cells aren't the same as normal human cells," Rudel says. "We'd love to know how sensitive normal cells are. That's something we're working on."
But she says you can imagine that if you have some abnormal cancer cells growing in breast tissue, a chemical mix including parabens might act like fertilizer, further encouraging their growth.
And she admits that these are cells growing in a petri dish in a lab. It's a very precise but simple way to test exposure, but it's not necessarily representative of what's going on inside the body, which is a much more complex system.
Q: Is it possible to avoid some sources of parabens?
Yes. Thanks to consumer pressure, more and more cosmetics and personal care products are going paraben-free. And if they are, they usually advertise that fact on their labels. A careful read of the ingredient list on cosmetics can also tell you if a product contains parabens.
A 2012 study tested 213 consumer products for 66 different chemicals, including three kinds of parabens. Some were conventional products, while others advertised themselves as "green" or alternative products.
Among the conventional products, parabens were detected in hand soap, body lotion, shampoo, conditioner, face lotion and cleanser, foundation, lipstick, mascara, hair styling products, and sunscreen.
When researchers tested the green versions of those products, though, the parabens, and many other kinds of concerning chemicals, were much less common.
"Generally, I would say that you can reduce your levels by choosing more green products," says Dodson, who led the study.
As more companies drop parabens from their products, Americans' levels of these chemicals seem to be going down, according to CDC data.
"We know from looking at those [data] that levels have been dropping quite rapidly from 2005 to 2011," Rudel says. "I'd attribute that to consumer pressure."
SOURCES: Ruthann Rudel, MS, co-director of research, Silent Spring Institute, Newton, MA. Claire Philippat, PhD, post-doctoral researcher, the University of California at Davis. Robin Dodson, ScD, a research scientist at the Silent Spring Institute, Newton, MA. Environmental Health Perspectives, Oct. 27, 2015. CDC: Biomonitoring Summary, Parabens. FDA: "Parabens."
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