Well: A Warning on Chemical Peels

Poison Pen

Deborah Blum writes about chemicals and the environment.

In the late 19th century, German scientists discovered that an easy-to-make acid could rather neatly peel off a layer of skin cells. They promptly marketed it for "skin rejuvenation." Today, that compound, trichloroacetic acid, or TCA, is widely used by dermatologists both to brighten up aging faces and to remove damaged skin cells, including precancerous ones.

More than one million people received chemical peels from dermatologists in 2012, according to the American Society of Plastic Surgeons. The procedures can be performed with a variety of acids, but TCA is especially popular because it can reduce sun damage, pigment spots and acne scars. TCA is so popular, in fact, that it is sold in do-it-yourself formulas at pharmacy chains like Walgreens and online retailers like Amazon.

But a growing number of studies, mostly in laboratory animals, have suggested that TCA has troubling, more destructive effects. Recently the International Agency on Cancer Research moved to classify it as a suspected human carcinogen, and in July, the state of California followed suit, announcing its intent to add TCA to the state registry of toxic substances. Researchers have been taking a hard look at TCA's safety both for patients and practitioners.

"When there's evidence of carcinogenicity in animals, we assume it has the potential to cause harm in humans," said Martha Sandy, chief of the Reproductive and Hazard Assessment Branch of the California Environmental Protection Agency. Even if the evidence is uncertain, she said, it is important that both consumers and businesses be told of potential risks.

"One of the purposes of putting a compound on the list is to make the public aware of the current state of scientific knowledge," Dr. Sandy said.

You don't have to get a chemical peel to be exposed to TCA. It is used as an antiseptic, a soil sterilizing agent and a reagent in pharmaceutical manufacturing; it turns up in drinking water as a byproduct of chlorination, and as a metabolite of some industrial solvents and some medications, like chloral hydrate, a common sedative. Research with animals shows that it can be absorbed both in drinking water or through dermal exposure, seeping through the skin into the bloodstream.

Concern about the acid has been growing since the 1990s, when early studies began linking it to cancers in animals. The California E.P.A. first flagged it as a potential carcinogen in 1999, but decided the evidence wasn't strong enough to say more.

But scrutiny intensified after a 2011 review by the federal Environmental Protection Agency, which cited study after study in lab mice linking TCA to liver cancer; one research group called it a "complete carcinogen."

Although the bulk of the TCA studies involve animals, a few human studies also hint at harm. A report published this summer in the journal Environmental Science and Pollution Research found evidence of both genetic and cellular damage in human subjects.

But such research is rare. The federal E.P.A.'s analysis emphasized the dearth of good human studies: "No human epidemiology or occupational studies of TCA were located. Case reports and accounts of the medical use of TCA for skin treatments demonstrate its potential for skin corrosion and eye irritation. However, no information on systemic toxicity following dermal exposure of humans to TCA was identified."

So do chemical peels with TCA raise your risk of cancer? "The short answer is, nobody knows," said Dr. Michael Hadley, an associate professor of dermatology at the University of Utah and a co-author of a chapter on TCA in the Color Atlas of Chemical Peels. "I can tell you that the link is not proven or shown in any human studies. But that's partly because we haven't done the long term research that would give us all the answers."

Dr. William Coleman, the editor in chief of the journal Dermatologic Surgery, points out that the cancer findings derive from long term exposures in laboratory animals. A person receiving a chemical peel, on the other hand, is exposed to TCA for only a few minutes before the acid is washed off. Further, TCA causes a mild coagulation of skin proteins, which he said should reduce absorption of the acid into the bloodstream.

"I continue to use TCA without hesitation," he said.

Even public health advocates admit that it's difficult to assess the risk. "Cancer is complicated, exposures are complicated, and it's ethically difficult to do the kinds of human studies that might tell us what we really want to know," said Caroline Cox, research director of the Center for Environmental Health, an advocacy group in Oakland, Calif. "In the universe of chemical compounds used in commerce, there are so few that have been thoroughly tested."

The greatest concern may be for those who are exposed on a regular basis, including practitioners who regularly apply peeling agents and consumers using over-the-counter products a bit too enthusiastically.

Both Dr. Coleman and Dr. Hadley noted that TCA sales are poorly regulated and that it is far too easy to purchase it without fully understanding the risks. Aside from the toxicity concerns, this is a powerful acid, and if applied incorrectly it can burn skin severely enough to cause permanent damage.

Meanwhile, "we're paying attention to the studies that raise concern with long toxicity," Dr. Hadley said. The California EPA plans further analyses during the next year as the agency determines whether warning labels should be required on products containing the acid.

In the meantime, Dr. Hadley adds, "I think there's a certain amount of care that should be used." TCA isn't the only option for those seeking rejuvenated skin; there are milder peeling agents, such as glycolic acid, as well as dermabrasion and laser resurfacing treatments. Consult with a clinician before making a choice.

Dr. Cox noted that the reevaluation of TCA by California in particular could bring new and safer products to the market. "It's often an incentive to innovate," she said.

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