As people plan more outdoor activities this summer, some pregnant women may be wondering which insect repellent will protect them best. This year’s concern is Aedes aegypti and Aedes albopictus mosquitos, whose bites have the potential to transmit Zika virus. The virus has caused brain abnormalities in babies developing in the womb.
According to Patrick Ramsey, M.D., M.S.P.H., staying inside; getting rid of standing water outside; wearing light-colored, long-sleeve shirts and long pants when outside; and using a mosquito repellent containing DEET are the best ways to guard against Zika.
DEET is the gold standard
“DEET is the gold-standard ingredient in insect repellents,” said Dr. Ramsey, a maternal-fetal medicine specialist at UT Medicine San Antonio. UT Medicine is the faculty practice of the School of Medicine at the UT Health Science Center San Antonio. Dr. Ramsey delivers babies at University Health System, one of the UT Health Science Center’s clinical partners.
“We know from several large studies that about one-third of the U.S. population, including pregnant women, have used or are currently using mosquito repellents containing DEET. DEET doesn’t kill mosquitos. It impairs the mosquitos’ ability to locate and bite a victim,” he said.
“These repellents are safe for large-scale uses, such as city spraying initiatives, and for personal use,” he said. “The skin is a good barrier for preventing chemicals from getting absorbed into the body. A small amount of DEET does get absorbed, but it is excreted in the urine. DEET has shown no significant adverse outcomes for pregnant and non-pregnant patients.”
DEET was developed to protect U.S. troops during World War II and became available to the general public in the 1950s. Since then, studies have shown that it is the most effective ingredient in mosquito repellents.
Studies show DEET’s effectiveness
A 2001 “Perspective” article in the New England Journal of Medicine, conducted after outbreaks of West Nile Virus and Lyme Disease, found that insect repellents containing DEET “protect significantly longer than other synthetic and botanical repellants.” The study recommended a DEET concentration of about 35 percent for long periods of outdoor exposure. Repellents with lower concentrations are acceptable for short periods outside. The study said concentrations of more than 50 percent did not offer improved protection other than for a longer period of time.
The results were repeated in a 2015 study in the Journal of Insect Science. “For both species (Aedes Aegypti and Aedes albopictus), the researchers found that mosquitoes were strongly repelled by all products containing DEET. For other products, they found mixed results,” the study stated.
Dr. Ramsey added that a large study of 897 pregnant women in Thailand published in 2001 in the American Journal of Tropical Medicine found similar results. The study compared DEET to a placebo for the prevention of malaria. “They looked at levels of DEET in the maternal blood and in the placenta to see if it crossed into the placenta,” Dr. Ramsey said.
“Of the women with cord blood available, they detected DEET in only 8 percent of women who had received DEET-containing mosquito repellants. It tells us that DEET does cross the placenta but it doesn’t cross the placenta very well,” Dr. Ramsey explained. “It was mostly excreted in the urine.
“That same study also looked at the outcomes of the babies whose mothers used DEET mosquito repellants. They saw no differences or adverse effects in those babies. This included no evidence of neurological damage, skin changes or intestinal problems.”
Learn more about preventing mosquito bites
The Centers for Disease Control and Prevention lists DEET repellents first among its recommended products. “Use Environmental Protection Agency-registered insect repellents with one of the following active ingredients: DEET, picaridin, IR3535, oil of lemon eucalyptus, or para-menthane-diol. Choosing an EPA-registered repellent ensures the EPA has evaluated the product for effectiveness. When used as directed, EPA-registered insect repellents are proven safe and effective, even for pregnant and breast-feeding women,” the CDC website states. Visit http://www.cdc.gov/zika/prevention/ for more information.