Sunscreen lotions used by tourists worldwide are a major cause of coral bleaching - a condition that leads to the death of the organism and the collapse of delicate ocean eco-systems - according to a new study.
In the study, chemical compounds that make up the ultra-violet filters that wash off the skin of swimmers in the tropics were shown to be a major cause of bleaching of coral reefs even in small quantities.
The researchers, who were led by Roberto Danovaro, at the University of Pisa in Italy, called for a set of laws 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," Times Online quoted the authors, as saying.
"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," they added.
The researchers further said that out 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.
They said that a 20-minute dip in the sea could wash off about a quarter of the chemicals in the sun lotion.
"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," the researchers said.
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," he added.
Researchers conducted the study in seawater surrounding coral reefs in Mexico, Indonesia, Thailand and Egypt.
They found that even small doses of sunscreen caused large discharges of coral mucous - a clear sign of environmental stress - within 18 to 48 hours.
The study showed that 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 is published in the journal Environmental Health Perspectives.