Sprays that kill insects are bad news for people, too.

RODALE NEWS, EMMAUS, PA—Your attempt to deter Lyme disease–carrying ticks and West Nile–infected mosquitoes from latching on to you could open the door to other health threats, emerging studies suggest. The latest evidence, published in the journal Occupational and Environmental Medicine, found that pregnant women who use bug repellents have a higher likelihood of giving birth to a child with a common birth defect.

THE DETAILS: Spanish and British researchers looked at 471 cases of baby boys born with hypospadias, an increasingly common birth defect in baby boys where the urethra opening is on the underside, not at the end, of the penis. Corrective surgery is generally successful in fixing the problem. The scientists also included a group of 490 healthy children as a control.

In the study, researchers inquired about family members' use of insecticides, including bug repellents, in the home and garden, and their home's distance from agricultural operations where chemicals are commonly used. Participants answered questions regarding use of fly strips, pesticides, insect spray, bug repellent, rat poison, ant powder, flea treatment, and lice shampoo. Researchers added up the exposure and found that a high score increased the risk of hypospadias by 73 percent; insect repellent use within the firth three months of pregnancy correlated to an 81 percent increased risk.

WHAT IT MEANS: Other scientific research has linked hypospadias, which occurs in about two out of every 500 boys, to other environmental exposures, but this was the first to make a connection between bug repellent, which commonly uses the chemical DEET as an active ingredient, to the birth defect. A study published last year in the journal Environmental Health Perspectives found an association between hairspray and birth defects, while other studies point to pesticide exposure (particularly DDT and lice-killing lindane), and exposure to phthalates at work. Phthalates are chemicals with estrogenlike properties used to make some plastics more flexible, and to help disperse fragrances. University of Rochester researchers recently found that these chemicals, found in hairsprays, cleaning products, soaps, and vinyl, cause boys to exhibit fewer masculine qualities.

This new study raises new concerns about harmful consequences of pesticide exposure. Still, the finding shouldn't be all that surprising; a number of studies have linked DEET to other health problems, including asthma attacks, death from ingestion, and seizures. A study appearing recently in a British journal suggested DEET can interfere with proper functioning of your central nervous system because of its ability to inhibit the activity of the enzyme cholinesterase.