(Beyond Pesticides, December 3, 2009) Pregnant women should reconsider applying insect repellent after a study finds a link to an increasingly common birth defect. European researchers have found an association between mothers who used insect repellent in the earliest phase of pregnancy and an increased rate of “hypospadias” in the penises of their male children.
Hypospadias is the condition where the opening of the penis is in the wrong place – usually back from the tip and on the underside – and often requires corrective surgery. The condition is thought to affect around one to two baby boys in every 500. According to a report published online November 30 in Occupational and Environmental Medicine and entitled “Use of biocides and insect repellents and risk of hypospadias,” infants born to mothers who used insect repellent during the first trimester of pregnancy are more likely to have hypospadias (OR 1.81, 95% CI 1.06 to 3.11) after adjusting for other factors.
The research includes 471 babies with hypospadias and 490 acting as a comparison group. Their mothers were asked a series of questions, including whether they had been exposed to insect repellents and biocide chemicals, such as pesticides or weedkillers. They were asked about their own use of fly sprays, repellents, animal poisons, pet flea treatments and nit shampoos and asked geographical questions, for example if they lived less than a mile from an agricultural field. Exposure levels were then calculated using a score from 0 to 8.
A high total pesticide exposure was associated with an increased risk (73%) for hypospadias. Insect repellent use in the first three months of pregnancy was linked with an 81% increased risk of hypospadias. The researchers found no significant links between the birth defect and individual pesticides.
“We found a significant association for risk of hypospadias with the use of insect repellents and total biocide score, but not with the use of individual biocides or indicators for its use,” Mark J. Nieuwenhuijsen, MD, of the Center for Research in Environmental Epidemiology at Parc de Recerca Biomedica de Barcelona, and colleagues wrote.
“Further work should be conducted on the possible reproductive effects of insect repellents, with consideration of the type, content, and mechanisms of action of specific formulations, and the current findings need to be replicated before firm conclusions can be drawn.”
A number of studies have also found associations between pesticide exposure and risk of hypospadias, but none had explored whether the use of insect repellents increased the risk. While the researchers found no direct link between individual pesticides and hypospadias, they theorized that association between total pesticide exposure and the birth defect might indicate exposure to some other toxic compound.
Scientists describe a group of impacts on the male reproductive system under the term Testicular Dysgenesis Syndrome (TDS). TDS includes the birth defects cryptorchidism and hypospadias, as well as poor semen quality (i.e. reduced sperm count, abnormal sperm), decreased fertility and perhaps also testicular cancer. Scientists suspect chemical exposures during pregnancy, specifically during the time when the male reproductive system is developing, may be causing these related impacts. Scientists suspect that TDS results from chemicals that can disrupt hormones, known as endocrine disruptors, and include chemicals such as PCBs, dioxins and some pesticides.
The researchers in this study note that insect repellents can contain compounds such as N,N-diethyl-m-toluamide, better known as DEET, which can cross the placental barrier and can be toxic at high doses. For years scientists have raised concerns about the use of DEET and seizures among children, even though the U.S. Environmental Protection Agency (EPA) claims that there is not enough information to implicate DEET with these incidents. DEET is quickly absorbed through the skin and has caused adverse effects including severe skin reactions including large blisters and burning sensations. Laboratory studies have found that DEET can cause neurological damage, including brain damage in children.
DEET’s synergistic effect with other insecticides is also a major health concern. DEET, when used in combination with permethrin – a synthetic pyrethroid insecticide, likely facilitates enhanced dermal absorption of permethrin and induces symptoms such as headache, loss of memory, fatigue, muscle and joint pain, and ataxia, which causes an inability to coordinate muscular movements.
There are many least-toxic options for repelling insects that include the use of citronella and other essential oils, like oil of lemon eucalyptus, which has been recommended as an efficacious alternative by the Center for Disease Control and Prevention (CDC). For more information on safer methods to protect yourself from insects, please visit Beyond Pesticides’ fact sheet on repellents.