Suntan lotions used to protect against harmful ultraviolet radiation could themselves contain poisonous ingredients which kill skin, research disclosed today.

A chemical used in 90 per cent of sunscreens worldwide might itself be toxic, a team of Norwegian scientists have found.

Exposure to the sun could make the UVB filter octyl methoxycinnamate (OMC) even more deadly, according to a report in New Scientist magazine.

Tests conducted by the Norwegian Radiation Protection Authority found that half of mouse cells died when they came into contact with a weak dose of OMC, at a much lower concentration than is used in sunscreens.

Shining a lamp on the OMC-impregnated cells, to simulate sunshine, made the chemical twice as deadly.

NRPA biophysicist Terji Christensen said he believed some sunscreens could damage human skin and warned sunbathers to use sun screens "with caution".

"They should only be added when other protective measures cannot," he added.

Rona MacKie, a dermatologist from the University of Glasgow, highlighted the difficulties of extending the research's findings from mice to humans but agreed that sunscreen should only be used as a last line of defence against UV radiation.

The Cosmetic Toiletry and Perfumery Association, which represents sunscreen manufacturers in Britain, said OMC has been "thoroughly tested for safety" and approved by regulatory authorities in Europe and the United States.