En español | When you go to a dermatologist now, you'll probably find brochures on products and procedures that will "turn back the clock." But how do they work, and are they worth the money and effort?

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Some of the most popular products for reducing fine lines are prescription-strength retinoids, which are vitamin A derivatives, marketed under the brand names Retin-A or Renova. Their active ingredient is tretinoin or the milder retinoid called retinol.

"Anytime I talk to people about skin care, basically I tell them to get the prescription drug Renova," says Linda Rhein, a biochemist with Bayer Healthcare Pharmaceuticals and editor of the 2009 book Aging Skin: Current and Future Therapeutic Strategies. "At least with Renova you know there were valid clinical trials conducted to prove that it works."

Over-the-counter skin care products contain lower concentrations of retinoids and may make the skin feel smooth, but they do little for wrinkles, according to ConsumerReportsHealth.org.

But one of those clinical trials on retinoids also showed that it may pose a cancer risk. When researchers tested tretinoin on a group of older male veterans, the study was halted because of a higher death rate, including from lung cancer, among men assigned to use tretinoin. The research was spurred by earlier evidence that retinoids may lower the risk of skin cancer. Researchers disagree over whether the tretinoin was to blame, but other studies have linked vitamin A products to lung cancer, writes dermatologist Kenneth Katz in an editorial about the study in a 2009 issue of the Archives of Dermatology.

"This is an inconvenient truth," Katz says. "Tretinoin is a great medicine — it's very effective — but this trial showed us there might be some big risks in using it."

Dermatology nurse Barbara McKeehen, a member of the Dermatology Nurses' Association, disagrees. "There have been no previous similar adverse events associated with tretinoin in all the years it has been available," she says. She also notes that the study participants were "typically elderly men who have been smokers."

Recent animal tests by the National Toxicology Program (NTP) also suggest that some retinoids may pose a cancer risk. John Bailey, a biochemist and now chief scientist at the industry-funded Personal Care Products Council, called for the testing when he worked for the Food and Drug Administration's cosmetics office. However, he now says that the NTP study was "very flawed" and should have been thrown out.

An FDA spokesperson said the FDA continues to believe that tretinoin "is a safe and effective product when used as labeled."

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