“Parabens,” the term for a group of preservatives used in mainstream beauty products, wasn’t always a dirty word.

In 2004, Dr. Philippa Darbre, a research scientist at the University of Reading in the UK, published a small but pioneering study that showed high concentrations of parabens in human breast tumors.

Women everywhere flipped over their moisturizers to read the list of ingredients.

“That first paper shocked people because it was the first time intact parabens had ever been measured in the human body,” says Dr. Darbre. And while the study did not show that the chemicals cause cancer, it sounded a serious alarm.

Why? Parabens, which prevent bacteria from growing in beauty and personal-care products, are able to mimic or interfere with estrogen in the body, and exposure to estrogen is one of the primary influences on the development of breast cancer.

Since then, several studies have detected and reported parabens in human urine and tissue. In response, many beauty companies have eliminated them from ingredient lists, though they’re still used in many mainstream products.

Now, Dr. Darbre has published two new studies that shed even more light on the ways parabens enter our bodies and how they affect our health.

Here’s what you need to know about the latest research (and before refilling your beauty bag):

1. Parabens are getting into your body. In March, Dr. Darbre and her team published the results of a study that replicated the original study done in 2004, with a much larger sample size. They looked at the concentration of five parabens in breast tumor tissue. One or more types were found in 99 percent of the tissue samples, and all five were measurable in 60 percent of the samples. “The take-home message was that we validated the earlier study with a much more substantial study. Parabens are getting into the breast, and they’re getting in in significant amounts,” she explains.

2. Yup, your skin is letting them in. The parabens identified in the study were primarily intact, meaning they’ve bypassed the liver. What does this mean? You’re not getting them from your food, they’re being absorbed through your skin.

3. Deodorants and antiperspirants aren’t the only bad guys. For a long time, Darbre thought deodorants and antiperspirants were most likely delivering parabens into breast tissue. (She cited close proximity and the fact that many breast cancers start in the area closest to the armpit). But seven people in the new study had never used deodorants or antiperspirants, and their concentrations of parabens wasn’t any lower. So, anything from moisturizer to sunscreen to eye makeup could be to blame. “I had to change my mind,” says Dr. Darbre. “I think it’s more about the total load on the skin across the body. What we still need to try to understand is how they can move around the body.”

4. Parabens are carcinogenic.Past research has focused on how parabens fuel the growth of existing cancer cells through their estrogenic activity. But in a second study published earlier this year, Dr. Darbre found that parabens may be carcinogenic, meaning they can transform healthy cells into cancer cells.

The takeaway, says Dr. Darbre, is that parabens are only a tiny slice of the problem. They’re just one of many chemicals we’re all exposed to in our day-to-day environment. “We’re going to see that the problem is long-term, low-dose exposure to a cocktail of chemicals,” she explains. “But the reason I’m keen on the personal-care products [issue] is that women have the option to stop using these things. I want to empower them to be able to make their own decisions.” —Lisa Elaine Held

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