US authorities have ruled two eczema creams should carry warnings that they may increase the risk of cancer.
The device could help children with eczema
The Food and Drug Administration said research had shown that Elidel and Protopic may pose a cancer risk when absorbed into the body.
It said babies should not be treated with the creams at all.
The view is strongly disputed by the manufacturers, Novartis, which makes Elidel, and Fujisawa Pharmaceutical, which makes Protopic.
The FDA is working on a "black box" warning for the creams - the strongest warning carried by medicines in the US.
In a statement it said animal studies had shown a potential link with cancer.
There were also reports of seven cases of lymphoma and six of skin cancer among children and adults treated with Elidel or Protopic.
Both creams work by suppressing the immune system. Depressing immune activity in this way is known to potentially contribute to cancer.
A spokesperson for the UK's Medicines and Healthcare products Regulatory Agency said it was closely monitoring the safety of the creams.
"Any patient or parent of a patient who has concerns about their treatment or their child's treatment should speak to their doctor."
Margaret Cox, chief executive of the UK's National Eczema Society, told the BBC News website the creams already came with strong warnings about their over-use in this country.
"Because they are new treatments one does have to recognise that the long term effects are uncertain," she said.
"To date we haven't had any evidence of direct causality between topical application of these creams in humans and cancer."
Novartis dismissed claims Elidel could increase the risk of cancer, and said it planned no immediate change in its product label.
In a statement it said: "Novartis agrees that patients suffering from mild to moderate eczema need to be informed about the safe and effective use of Elidel, but we believe a recommendation to add a black box warning to the label is unsubstantiated by clinical evidence and experience in more than five million patients worldwide."
National Institute for Clinical Excellence guidance
Treatment with tacrolimus (Protopic) or pimecrolimus (Elidel) should be initiated only by physicians with a special interest and experience in dermatology, and only after careful discussion with the patient about the potential risks and benefits of all appropriate second-line treatment options
Fujisawa Pharmaceutical said it had not found any data to clearly link Protopic to cancer, and believes it has provided sufficient information to ensure the drug is used safely.
The American Academy of Dermatology (AAD) has also questioned the FDA move, arguing that virtually none of the creams would get inside the body.
Dr Clay Cockerell, ADD president, said: "These are valuable medications, and if used properly they significantly reduce the debilitating impact of eczema and allow millions of our patients to live normal lives."
In February, members of an FDA advisory panel said they were concerned the companies were aggressively advertising the medicines to treat infants and others with skin problems that the creams are not approved to treat.