DEET seen as safe for pregnant women to avoid Zika despite few studies

Pregnant women waiting to see a doctor at a clinic in Tegucigalpa, Honduras, in February. Local mosquito transmission of Zika has been reported in the country.CreditOrlando Sierra/Agence France-Presse — Getty Images

(THE NEW YORK TIMES) This summer, some yellow-fever mosquitoes carrying the Zika virus are expected to arrivealong the Gulf Coast and elsewhere in the continental United States. Health officials are urging people to use insect repellents with DEET to avoid being bitten.

The mounting evidence that the virus isstrongly linked with birth defectsmakes this a priority for pregnant women. But is it safe to use repellents containing DEET with a baby on the way?

Although the scientific evidence is a bit thinner than some experts would like, most say the answer is yes, as long as you do not overapply.

Few published studies address the effects of DEET, short for N,N-diethyl-meta-toluamide, in mothers-to-be and their offspring. None involved pregnant women in the first trimester, the period when most birth defects occur.

Still, the existing evidence in pregnant women is reassuring. Even though there is not “a lot of” research, “it makes sense to use DEET to protect yourself from something we know is truly unsafe, like Zika,” said Dr. Laura E. Riley, a specialist who works with high-risk pregnancies and infectious disease at Massachusetts General Hospital.

A randomized trial of roughly 900 womenin Thailand, published in 2001, provides some of the strongest evidence that using DEET daily for months will probably not hurt a fetus.

A malaria infection in pregnancy can lead to miscarriage or stillbirth. To prevent it, half of the women in the study applied a 20 percent concentration of DEET mixed with a makeup called thanaka daily in their second and third trimesters. The other half wore only thanaka.

DEET can cross the placenta and reach the fetus, the researchers found. But DEET was detected in the blood of the umbilical cord in just four of 50 users.

Importantly, “the newborns weren’t affected in terms of growth or development from DEET exposure,” said Dr. Rose McGready, the study’s lead author and a professor of tropical maternal and child health at the University of Oxford. No adverse effects on growth were found among the children a year later, either.

But the study “didn’t include the first trimester,” Dr. McGready said. “That’s an important missing component.”

Asked about the paucity of published studies looking at DEET use in the first trimester, Jack Housenger, the director of the Environmental Protection Agency’s office of pesticides programs, replied in a statement, “DEET is safe, including for pregnant women at any stage.”

In 2014, a safety review by the E.P.A. did not identify “any risks of concern to human health” if the directions are followed. The agency’s review assessed the potential risks of long- and short term use of DEET in pregnant animals.

The Centers for Disease Control and Prevention counsels pregnant women to use any E.P.A.-registered repellent, including those with picaridin (a synthetic compound), IR3535 (a biopesticide) and DEET. In animal studies, the E.P.A. has found no evidence that either picaridin or IR3535 is harmful to the developing fetus.

DEET was registered with the E.P.A. for public use in 1957, picaridin in 2005 and IR3535 in 1999, but the last two were used abroad for years before.

Bob Peterson, a professor of entomology at Montana State University, published arisk assessmentof DEET and picaridin in 2008. Exposures are acceptable in adults and children if they are used “according to instructions on the package,” he said.

An estimated 104 million Americans use DEET every year, and reports of adverse events are “relatively small by comparison,” the E.P.A. wrote in its safety review.

Only minimal amounts of DEET cross into a pregnant mother’s bloodstream, suggesting babies are exposed to very little.

In 2010, researchers, including some from the C.D.C., analyzed the blood of150 pregnant women in New Jerseyand their umbilical cords for a range of pesticides.

“DEET was not at remarkable levels,” said Mark Robson, the study’s senior author and a professor of plant biology and pathology at Rutgers University. “Birth weight, length and circumference were all normal” for all infants.

Pregnant women who wish to be extremely cautious may use a repellent with a lower concentration of DEET to limit how much gets in their blood, said Dr. Sarah G. Obican, a maternal fetal specialist and a member of the Organization of Teratology Information Specialists.

“Using a 6 percent DEET product will last you two hours, and 20 percent one will last close to four hours,” Dr. Obican said. “Why not use the lower concentration and apply more often?”

A 1999 trial with 60 men and 60 women who used a 31 percent concentration of DEET foundwomen had significantly less protectionover time than men did from Anopheles stephensi mosquitoes.

Still, DEET “will give you the best protection, even if it doesn’t protect as long a duration for a woman as it does for a man,” said Dawn Wesson, an associate professor of tropical medicine at the Tulane University School of Public Health and Tropical Medicine.

Until a few years ago, DEET formulations smelled like a chemical, Dr. Wesson said, and “people have this perception that if it smells this way, it’s not safe, and that’s not true.”

Pregnant women in areas where the Zika virus is spreading are currently at far greater risk than those in the continental United States. The C.D.C. ispredicting that a quarter of Puerto Rico’s3.5 million people may be infected with the Zika virus within a year.

Dr. John Meeker, a professor of environmental health sciences at the University of Michigan School of Public Health, and others are following 1,000 pregnant women in Puerto Rico. They are tracking concentrations of pesticides, including DEET and two of its metabolites, in urine to see if there is any link to adverse pregnancy outcomes.