Health officials in the U.S. issued a public health advisory over the use of two eczema creams because of a potential cancer risk.

The U.S. Food and Drug Administration is also adding black box warning for the drugs - Elidel and Protopic - the strongest warning carried on medicines in the U.S.

Children under 2 year of age should not be treated with the creams at all, according to the FDA.

The FDA said data showed that the risk of cancer increased as the amount of the drug given increased.

"FDA advises that Elidel and Protopic should be used only as labeled, for patients who have failed treatment with other therapies," said an FDA statement.