Updated: Jul 19, 2017 - 6:08 PM

There's a new health warning about a chemical found in most sunscreens. A new study found when that chemical comes into contact with sun and chlorine, it can become toxic.

If you flip over your sunscreen, chances are avobenzone is first ingredient you'll find. In fact, Boston 25 News went into a couple of drug stores and found the vast majority of the sunscreens on the shelves have this chemical listed as the active ingredient. Avobenzone is the active ingredient in most sunscreens as it protects against UV rays.

“I have this one cause I bought it just for my daughter, but I don't even know if it has it. Oh, avobenzone there it is -- first ingredient. And [the sunscreen is made] for babies so that's not good,” said Candice Brown of Mattapan.

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“It's an incredibly common ingredient in sunscreen,” said Dr. Abigail Waldman, Brigham and Women’s Dermatologist.

But a new study first conducted in Moscow and published in the Chemosphere Journal, that's now being cited here in the United States found avobenzone can break down when exposed to a combination of light and chlorinated water, such as in a swimming pool and it can degrade into some very harmful compounds, some of which are known to cause cancer.

Health alert: an extremely common ingredient in your sunscreen could do more harm than good. A @BrighamWomens doctor has advice on @boston25 pic.twitter.com/myqnIiB2xA — Heather Hegedus (@HeatherHegedus) July 19, 2017

“Anytime you put on a sunscreen or a lotion, it can react with chlorine and byproducts can form, which are chlorinated byproducts that can potentially could be harmful and whether that's on your skin initially or it's floating in the pool and you get exposed, those are two main ways of having exposure,” said Dr. Waldman.

Waldman explains the particular concern is ingesting it.

“After swimming in a pool and putting your hand in your mouth or sucking your thumb,” said Dr. Waldman.

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Dr. Waldman's advice is to keep kids' hands out of their mouths, and towel or shower off immediately after pool time, and consider looking for a sunscreen with zinc.

Mothers we spoke with say they're going to make the switch.

“So yeah, we gotta think about that,” said Brown.

Dr. Waldman also says despite all of this, people shouldn't stop using sunscreen altogether.

She says using sunscreen, even with avobenzone, is better than using nothing at all because going without it can lead to skin cancer.

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