If your suntan oil can change the sex of fish, what can do it to you?

The stuff is not only on our skin: it's in our tap water and lunches too

Scientists have found that male hornyhead turbot and English sole, feeding near sewage outfalls on the Californian coast, are being feminised - and a chemical found in sunscreens is the likely culprit.

Meanwhile, Swiss researchers have found other suspected gender-bender chemicals from sun creams and oils building up in fish in their rivers.

Scientists at the University of California, Riverside, found that two-thirds of the male turbot and sole near a sewage outfall three miles off the surfers' paradise of Huntington Beach, near Los Angeles, were growing ovary tissue in their testes. A similar study by the Southern California Coastal Water Research Project found fish affected all along the coast. The American research is the first to find sex changes in fish in the open ocean.

Research on the feminising of fish in British rivers by the UK Environment Agency, exclusively reported in The Independent on Sunday, concluded in 2002 that oestrogen in urine from the contraceptive pill was to blame

But the University of California scientists found that the only culprit they could "exclusively identify" is oxybenzone, used to protect the skin from the ultraviolet component of sunlight.

Oxybenzone, which mimics oestrogen's chemical make-up, is washed off tanned bodies in the shower, passes through sewage works unchanged and settles on the seabed, where bottom-feeding fish eat it.

The scientists suspect the sunscreens are a contributory factor along with other pollutants, which they have yet to identify, such as DDT and PCBs. The new Swiss research, however, shows two other suspected gender-bender substances used in sunscreen and lip balm - octocrylene and 4-methylbenzylidene camphor - also building up alarmingly in fish.

They fear that people are being exposed to the chemicals several times over, first by putting them on their skin, and then injesting them in drinking water and the fish they eat. But the cosmetics industry denies the chemicals are dangerous, and says that"sunscreen phobia" could lead to more cancers. For, unlike other cosmetics, sunscreens unquestionably save lives. About 100,000 new cases of skin cancer are diagnosed in Britain each year, of which 7,300 are particularly deadly melanomas that kill more than 1,600 people a year. Cancer Research UK fears melanoma numbers will treble over the next 30 years.

However, there have been other concerns about potential health effects. Some clear sunscreens use nanoparticles so small that they can penetrate the skin and even get into the brain.

There is also concern about a the universal use of sunscreens. By shielding ourselves from sunlight, we produce less vitamin D, which protects against as many as 16 different cancers.