However, Christopher Bunick, MD, a board-certified dermatologist and associate professor of dermatology for the Yale School of Medicine — who studies benzene contamination in personal care products — says, “Here, benzoyl peroxide itself is unstable when placed in currently available formulations and/or vehicles and breaks down into the carcinogen benzene.” According to Dr. Bunick, the breakdown to benzene happens in the bottle or packaging, though the time it takes to break down may vary. “At room temperature it could be days to weeks or longer, and that will depend on the formulation and the storage parameters.”
Should we be worried?
That’s up for debate, depending on who you ask. On one hand, benzene is classified as a carcinogen. “It’s not a, ‘Maybe this is bad for you.’ Benzene has been known to cause cancer or significantly elevate the risk of cancer in human beings for decades,” explains Light. The International Agency for Research on Cancer (IARC), part of the World Health Organization, classifies benzene as “carcinogenic to humans,” as does the US National Toxicology Program.
“Long-term industrial exposure, meaning workers in manufacturing who are exposed frequently over tens of years to benzene, has been linked to cancer,” Dobos says. “I’d like to examine all the test methods and data [of the Valisure study], but some of the high numbers referenced are coming from testing of products that were subjected to high temperatures accelerating the breakdown of benzoyl peroxide into benzene.”
Dermatologists Allure spoke with are skeptical about taking benzoyl peroxide off the table entirely, too. “We need more data,” says Caren Campbell, MD, a board-certified dermatologist in San Francisco. “Even if the breakdown of benzoyl peroxide releases benzene, the penetrability of it through the skin has been questioned by toxicologists [previously] and the apples-to-apples comparison of the data to real life is also questioned by these reputable toxicologists.”
Dr. Campbell typically recommends patients use benzoyl peroxide as a face wash at a low percentage of five percent or less, versus having it sit on the skin, so they get the acne-fighting benefits of benzene without its potential for irritating the skin. “This is what I’ve always recommended and frankly, this is also a way to limit the time on the skin and limit the concentration if more data is discovered showing it’s an issue,” she says. Certain types of acne respond differently to certain topicals, though Dr. Campbell does advise patients to avoid benzoyl peroxide if they are pregnant, breastfeeding, or trying to conceive.