Insect repellents linked to genital defects in baby boys

Tuesday, December 1, 2009

British Medical Journal

Women who use insect repellents during the first three months of pregnancy are more likely to give birth to baby boys with a genital defect, according to researchers. Insecticides used in gardening and agriculture may also be linked to genital malformations in boys.

What do we know already?

Hypospadias is a birth defect that affects boys’ penises. It causes the opening to appear on the underside of their penis, rather than the tip. Boys born with hypospadias usually have an operation to correct it in the first few years of their life.

Hypospadias probably affects about 1 or 2 out of 500 boys, but not much is known about the causes. Researchers have been looking at whether contact with everyday chemicals during pregnancy is linked to a higher risk of having a baby boy with the condition.

In a study published last year, researchers interviewed the mothers of 471 boys born with hypospadias in the South East of England. Women who had regular contact with hairspray, such as those working as hairdressers, had a higher chance of having a boy with hypospadias. Researchers have looked again at the same group of women, this time looking at exposure to insect repellents, normally used on the skin, and insecticides, such as sprays used in gardening and agriculture.

Other research has already found that high doses of some insect repellents, such as DEET, can have harmful effects on pregnant rats. So far, studies looking at humans have found either no or low risks from using insect repellents. However, it’s impossible to rule out any risk without larger studies.

What does the new study say?

Women who had a son with hypospadias were more likely to have used insect repellents during early pregnancy, compared with women who had a healthy baby. However, the researchers didn’t ask about the specific products women used, so it’s impossible to say whether or which individual repellents might be linked to the increased risk. Different active ingredients include DEET and permethrin, while natural repellents contain essential oils of citronella or eucalyptus.

The researchers also looked at whether insecticides might be linked to birth defects. They looked at whether women lived near farmland, used pesticides in the garden, used fly sprays or ant powder, treated pets for fleas, or used nit shampoo. No single one of these things was linked to a higher risk, but women who had a combination of several were more likely to have a son with hypospadias.

How reliable are the findings?

Studies like this one can’t prove that insect repellents or insecticides are the cause of birth defects. We only know there’s a link. Women who use insect repellents may be different in lots of ways from women who don’t, so there could be other factors that play a part. However the researchers did adjust their findings to take account of other things which could affect the risk of hypospadias, such as smoking, the mother’s age, income, and the infant’s birth weight.

Where does the study come from?

The study appeared in a journal called Occupational and Environmental Medicine, which is published by the BMJ Group.

What does this mean for me? The researchers say that more research needs to be done on insect repellents before we can draw firm conclusions. There are probably several things that increase the risk of genital defects in boys, with smoking being another likely factor. It’s difficult to know just how big a part insect repellents or insecticides might play.

The outlook is reasonably good for boys born with hypospadias. Surgery can correct the problem in most cases, although no operation is completely without risk.

What should I do now?

There hasn’t been much research looking at whether individual insect repellents are safe during pregnancy. So it’s hard to know for certain what’s best at this stage. There may be times when you need to use them, for example if you’re travelling in a malarial area. Talk to your doctor if you’re in any doubt.

Research done last year suggested that taking folic acid supplements when trying to get pregnant might help protect your baby from hypospadias. Folic acid also helps prevent major birth defects like spina bifida. Official advice recommends you take a 400 microgram folic acid supplement (also called vitamin B9) from the time when you stop using contraception up to week 12 of your pregnancy.

Dugas J, Nieuwenhuijsen MJ, Martinez D, et al. Use of biocides and insect repellents and risk of hypospadias. Occupational and Environmental Medicine. Published online 1 December 2009.