The incidence of hypospadias has risen sharply in recent decades, and some experts have pointed the finger of suspicion at chemicals called phthalates, found in some plastics, including those found in hairspray.

Phthalates have the ability to disrupt hormones, and have been banned in toys in the EU for some years.

Certain phthalates have also been banned from hairsprays and other cosmetic products since January 2005.

However, no study has found a convincing link between women exposed to them and problems in their children.

The latest study looks not at personal use of hairsprays, but at their use, potentially in higher doses, by workers such as hairdressers and beauty therapists.

A total of 471 women whose babies had been born with hypospadias were interviewed, as were a similar number of women with unaffected children.

The women gave birth in 1997 and 1998 and were interviewed between 2000 and 2003.

Roughly double the number of women in the "hypospadias" group revealed that they had been exposed to hairspray through their job compared with those with unaffected babies.

No proof

However, Professor Paul Elliott, who led the study, said that the finding did not prove that hairspray - or any phthalates it contained - was the cause of this.

He said: "Women shouldn't be alarmed. This study adds a bit more evidence to the general picture about these chemicals, but more research will be needed to demonstrate that the link exists.

"Pregnant women will need to make their own choices about whether or not to avoid these kind of exposures."

Professor Andreas Kortenkamp, the head of the Centre for Toxicology at the School of Pharmacy, University of London, said that it was "important research"

He said that the UK government should consider taking the approach used by the Danish authorities, which has issued advice to women about the evidence linking phthalates to health problems.

He said: "I don't think we can continue to leave women alone to make decisions about these things - they need a bit of guidance, to know where these chemicals are.

"Certainly, if this was the mother of my children who was pregnant, I would strongly advise her to stay away from these."

Leap of faith

Professor Richard Sharpe, from Edinburgh University, said it was a "big leap of faith" to conclude phthalates were to blame for birth defects.

He said research had shown phthalates could suppress production of the male sex hormone testosterone - which plays a role in penis development - in some animals, but evidence that it had the same effect in humans was inconclusive.

"My advice has long been that women who are planning a pregnancy should avoid (or at least minimise) use of cosmetics, body creams/lotions etc, especially in the first three months of pregnancy.

"This is not because we know that the ingredients can do harm to the baby, but because it can only do good for the baby to avoid unnecessary chemical exposures."

Another finding of the study provides further backing of the government's recommendation that pregnant women should take extra folate to prevent similar defects to hypospadias, which arise early in pregnancy.

Women who took folic acid in the first three months of pregnancy were a third less likely to have a baby with hypospadias, according to the study.