British scientists from Imperial College London say women who are exposed to hairspray in the workplace during pregnancy have more than double the risk of having a son with the genital birth defect hypospadias.
The number of cases of hypospadias has risen sharply in recent decades, and the finger of suspicion has now been pointed at chemicals called phthalates, including those found in hairspray.
According to a new study by the Imperial College team this is the first research to reveal a significant link between hairspray and hypospadias, one of the most common birth defects of the male genitalia, where the urinary opening is displaced to the underside of the penis - the causes of the condition are often unclear.
The researchers suggest that if women are exposed to hairspray in the workplace in their first trimester of pregnancy, they have a two to three-fold increased risk of having a son with hypospadias.
The research suggests that hairspray and hypospadias may be linked because of chemicals in hairspray known as phthalates which have previously been suspected of disrupting the hormonal systems in the body and affecting reproductive development - phthalates are found in some plastics 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.
Hypospadias is thought to affect around 1 in 250 boys and can be successfully treated with corrective surgery after a boy reaches his first birthday - more severe cases can lead to problems with urinating, sexual relations and fertility.
Other research has previously suggested that hypospadias might be linked to vegetarianism but the new study did not show any increased risk in women who had a vegetarian diet during pregnancy - it also revealed that taking folic acid supplements in the first three months of pregnancy is associated with a 36% reduced risk of bearing a child with the condition.
Experts recommend pregnant women take folic acid supplements until the twelfth week of pregnancy in order to prevent neural tube defects such as spina bifida.
Professor Paul Elliott from the Department of Epidemiology and Public Health at Imperial College London, says hypospadias if left untreated, can cause problems in later life and although surgery to correct it is usually successful, any surgery will be traumatic for the child and his parents.
Professor Elliott says it is encouraging to find that taking folic acid supplements in pregnancy may reduce the risk of a child being born with the condition but more research is needed to understand why women exposed to hairspray at work in the first 3 months of pregnancy, may have an increased risk of giving birth to a boy with hypospadias.
The researchers conducted detailed telephone interviews with 471 mothers whose sons had been referred to surgeons for hypospadias and 490 controls, across 120 London Boroughs and Local Authority Districts.
The questionnaires explored a range of aspects of the women's health and lifestyle, including the mother's occupation and possible exposure to different chemical substances, family history of disease, maternal occupation, vegetarianism, smoking and use of folate supplements.
Professor Elliott, who led the study, says while the finding did not prove that hairspray - or any phthalates it contained - was the culprit - it does provide a little more evidence about these chemicals, but more research will be needed to demonstrate that the link exists and pregnant women will need to make their own choices about whether or not to avoid these kind of exposures.
Experts say this new study is "important research" and women need to be given the evidence linking phthalates to health problems; they suggest 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 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.
Researchers from University College Cork and the Centre for Research in Environmental Epidemiology in Barcelona also contributed to the study which is published in the journal Environmental Health Perspectives.
The study was funded by a grant from the UK Health and Safety Executive, the Department of Health, the Department of the Environment, Transport and The Regions and the European Chemical Industry Council.