Mercury poisoning doesn’t sound fun, but it also doesn’t necessarily sound like something the average consumer runs into a lot in modern cosmetic aisles, what with federal regulations banning dangerous levels of the stuff. However, there are a slew of illegal skin care products for sale out there that contain mercury, and the Food and Drug Administration doesn’t want folks slathering them on their bodies.

The FDA says many cosmetics marketed as “anti-aging” or “skin-lightening” contain mercury, and are usually marketed as treatments that remove age spots, freckles, blemishes, and wrinkles. Young people may also use them as acne treatments.

So how will you know if there’s mercury? Check the label, the FDA says: if the words “mercurous chloride,” “calomel,” “mercuric,” “mercurio,” or “mercury” are listed, mercury’s in it and you should stop using the product immediately.

What if there are no ingredients listed? Don’t assume it’s fine, the FDA warns.

“Federal law requires that ingredients be listed on the label of any cosmetic or nonprescription drug, so do not use a product that doesn’t have a label,” the agency advises. “In addition, don’t use drugs or cosmetics labeled in languages other than English unless English labeling is also provided. That’s also a sign that the product may be marketed illegally.”

These kinds of products are usually manufactured abroad and then sold illegally stateside, Jason Humbert of FDA’s Office of Regulatory Affairs explains, often in stores that cater to the Latino, Asian, African, or Middle Eastern communities. They’re also promoted online on social media, sold through mobile apps, and some people may bring them back from other countries for personal use as well.

“Even though these products are often promoted as cosmetics, they also may be unapproved new drugs under the law,” says Linda Katz, M.D., director of FDA’s Office of Cosmetics and Colors.

According to the FDA, mercury compounds are easily absorbed through the skin, and tend to accumulate in the body. They may cause allergic reactions, skin irritation, or neurotoxic problems.

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