For now, the message from the experts is urgent but restrained: Don’t panic, but do be prepared.
Pregnant women, especially, are being instructed to avoid areas where Zika is transmitted locally, and to take extra precautions to protect themselves from mosquito bites. That means making sure there are screens on open doors and windows; wearing long sleeves, socks, and pants outside; and using insect repellent once mosquito season gets under way.
But which bug sprays are safe for pregnant women?
Research into the use of various chemicals during pregnancy hasn’t been robust, but there are several studies that support the safety of chemicals commonly found in insect repellents. One randomized, double-blind trial involving nearly 900 women found that when DEET was applied regularly in the second and third trimesters, it could cross the placenta, but it didn’t have any adverse effects on a baby’s survival, growth, development at birth, or development at one year old.
That study didn’t include any women in early pregnancy, but researchers say the results of a separate animal-based experiment conducted in 1994 offer reassuring evidence that DEET is safe in the first trimester. In that study, with one exception, the offspring of rats and rabbits given massive doses of DEET didn’t suffer any ill effects. Because the highest dose was orders of magnitude higher than the normal human dose, researchers wrote in a paper for the Canadian Medical Association Journal in 2003, it appears that DEET is safe when used as recommended.
That’s in line with recommendations from the Centers for Disease Control and Prevention, which say it’s safe for women at any stage of pregnancy (and nursing moms) to use insect repellents containing DEET (up to 30 percent concentration), the synthetic compound picaridin (20 percent), or the biopesticide IR3535 (20 percent)—as long as they’re registered with the Environmental Protection Agency. (You can check the EPA database here.)
Shirts and pants treated with the insect-repellent permethrin are also considered safe. (Permethrin is also the active ingredient in many shampoos used to treat lice; and the U.S. Army has treated its combat uniforms with the chemical since 2013.)
“The evidence is reassuring that DEET, when used as directed, is safe,” said Peggy Honein, one of the leaders of the Pregnancy and Birth Defects Team for the CDC’s Zika response. “For permethrin-treated clothing, the data is also very reassuring. We would encourage pregnant women to use these methods to prevent mosquito bites, particularly if they’re in a place where there’s local transmission, but to use them as intended.”
In other words, don’t bathe in the stuff. In fact, the CDC recommends using “just enough repellent to cover exposed skin or clothing,” and rinsing off once you’re back indoors. Those who want to be particularly cautious could opt for insect repellent with lower concentrations of chemicals, which would have to be reapplied more often.