Chemicals in food, cosmetics and cleaning products are 'feminising' unborn boys and raising their risk of cancer and infertility later in life, an expert warns today.
Professor Richard Sharpe, one of Britain's leading reproductive biologists, says everyday substances are linked to soaring rates of birth defects and testicular cancer, and to falling sperm counts.
The government adviser's report published today is the most detailed yet into the threat posed to baby boys by chemicals that block the action of the male sex hormone testosterone, or mimic the female sex hormone oestrogen.
Professor Sharpe says many could be harmless on their own - but warned that their cumulative effect could be devastating for developing foetuses and warned women trying for a child to avoid them.
'You can't do anything about chemicals in the environment but you can control what you expose a baby to through your lifestyle choices,' he said.
'Because we don't know the complete list of chemicals that may be hormone disrupters, and we don't know how they interact, we can't point a finger at an individual chemical.
'The message is to avoid them, just as you should avoid alcohol and drugs.'
Doctors are concerned about rising levels of birth defects, with 7 per cent of British boys born with partially descended testes and seven in 1000 with malformed genitals.
The latest estimates indicate that one in six men in the UK has a low sperm count and will struggle to father a child.
And the number of testicular cancer cases among men in their 20s and 30s has been doubling every 25 years.
Following an analysis of available evidence, Professor Sharpe concluded that gender-bending chemicals are 'likely to account for a proportion' of birth defects in baby boys - and the testicular cancer and fertility problems the boys may suffer later in life.
His report looked at studies into birth defects of boy's genitals, low sperm counts and testicular cancer - a range of problems collectively called Testicular Dysgenesis Syndrome or TDS.
In repeated experiments, testosterone-disrupting chemicals found in pesticides, drugs, plastics and household products created symptoms of TDS in laboratory animals. Some of the experiments showed that the chemicals work in combination - causing problems at doses where the individual chemicals should be harmless.
The evidence that the chemicals cause problems in humans was weaker, but still showed a link between environmental chemicals and male fertility problems, the report said.
In one study, scientists looked at families moving from countries with a low rate of testicular cancer to Denmark - which has one of the highest rates of the disease in Europe.
First-generation immigrants had the same level of cancer as their country of origin. But their children - conceived and born in Denmark - had a similar risk to Danes. That indicated something in the environment was to blame.
Other studies have shown that mothers exposed to chemicals used in plastics, flame retardants and pesticides are more likely to have sons who go on to develop testicular cancer.
Exposure to environmental chemicals slightly increases the risks of undescended testes and hypospadia - malformed genitalia - in boys, the report found.
Professor Sharpe said TDS has its origins in the period between the eighth and 12th week of pregnancy, when exposure to hormone-mimicking chemicals can interfere with testosterone production in a foetus, preventing the sex organs from developing normally.
Chemicals shown to cause problems include pesticides such as DDT, fungicides such as vinclozolin; a group of chemicals called PCBs used in electrical circuits, paints, flame retardants and glues; and phthalates, which are used to soften plastics.
Elizabeth Salter Green of the charity CHEM Trust, which commissioned Professor Sharpe's report, said: 'Chemicals that have been shown to act together to affect male reproductive health should have their risks assessed together.
'Currently that is not the case, and unfortunately chemicals are looked at on a individual basis.
'Therefore Government assurances that exposures are too low to have any effect just do not hold water because regulators do not take into account the additive actions of hormone-disrupting chemicals.'
She advised pregnant women to keep cosmetic use to a minimum, choose unscented products, stop using perfume, avoid colouring hair and avoid DIY.