The U.S. Food and Drug Administration is proposing a ban on over-the-counter sales of skin-lightening products, saying potential health risks mean they should not be sold without a prescription.

The creams typically contain a drug called hydroquinone, a possible carcinogen also linked to a skin-disfiguring condition, the FDA said.

While the actual risk of the drug is unknown, the agency said the products should be restricted to prescription use under medical supervision.

An estimated 65 companies in the United States sell roughly 130 different skin-bleaching creams and other products that contain hydroquinone, the FDA said.

Studies on rodents show only "some evidence" that hydroquinone may cause cancer. However, the drug's link to a disfiguring condition called ochronosis has been widely documented since 1975 in black women and men in South Africa, Britain and the U.S.

The condition is marked by the darkening and thickening of the skin, as well as the appearance of tiny dome-shaped bumps and greyish-brown spots, the FDA said. Studies report the signs have appeared in users even after short-term use of the creams.

Since 1983, South Africa has limited the concentration of hydroquinone in skin-lightening products to two per cent to combat ochronosis.

Under the proposed FDA rule, all skin-bleaching products — prescription and over-the-counter — would be considered new drugs. Manufacturers would have to seek FDA approval to sell them and only then with a doctor's note.

The FDA published the proposed rule Tuesday in the Federal Register. The agency will accept public comments through Dec. 26. It was not immediately clear when the rule could become permanent.

In 1990, the FDA declared as unsafe another skin-bleaching drug, ammoniated mercury.