Tourists heading to the tropics were warned yesterday that their suntan lotion can kill off one of the main attractions of their holiday - the colourful corals that thrive in warmer waters. Residues from sunscreens that wash off in the sea were shown by researchers to cause coral bleaching, a condition that leads to the death of the organism and the collapse of delicate ocean eco-systems.

Chemical compounds that make up the ultra-violet (UV) filters in sunscreens, which are essential to protect the skin against burning, were shown to be harmful to coral reefs, even in small quantities.The researchers called for regulations to limit human contact with reefs where the coral was already suffering from other environmental threats such as rising sea temperatures.

“Different sunscreen brands, protective factors and concentrations were compared, and all treatments caused bleaching of hard corals,” said the researchers, who were led by Roberto Danovaro, at the University of Pisa in Italy, in the journal Environmental Health Perspectives.

“The coral response to sunscreen exposure was not dose dependent, as the same effects were observed at low and high sunscreen concentrations. The impact of sunscreens would be expected to be crucial in atolls and coastal coral reefs with low water renewal and strong tourist vocation.

"Our results provide strong scientific evidence of the potential impact of these products in tropical habitats and represent a pointer for outlining specific regulations for protecting coral reefs,” the team said.

The researchers added that, of the 10,000 tonnes of UV filters produced every year globally, about 10 per cent would be used by the 78 million tourists who visited the tropics.

A 20-minute dip in the sea could wash off about a quarter of the chemicals in the sun lotion, they said. They concluded: “According to these estimates, we believe that up to 10 per cent of the world's coral reefs would be threatened by sunscreen-induced coral bleaching.”

Coral is already under threat from global warming and one sixth of the world's population of coral was estimated to have been killed off by freak weather conditions in 1998.

John Bythell, a coral expert from the University of Newcastle, said: “Coral bleaching as a worldwide phenomenon is a problem because it kills the coral and the coral is supporting the entire reef, which is the prime coastal defence in the tropical world.

“In most of the developing countries coastal tourism is a major draw and an important source of income. The coral is getting closer and closer to its stress limits for survival.”

The research took place in seawater surrounding coral reefs in Mexico, Indonesia, Thailand and Egypt. Even small doses of sunscreen caused large discharges of coral mucous - a clear sign of environmental stress - within 18 to 48 hours. Virus levels in the seawater increased to 15 times the level found in control samples, suggesting that sunscreens might stimulate latent viral infections, the study found.

Sunscreens are made of about 20 compounds acting as UV filters and preservatives. Seven, including parabens, cinnamates, benzophenones and camphor derivatives, had negative effects.

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