Study Raises Concerns About Possible Reproductive Harms of DEET

Researchers from Harvard Medical School have uncovered new evidence linking the use of diethyltoluamide (DEET)-containing products to reproductive problems, including infertility, miscarriage, and birth defects. Using worm models, they found that DEET may negatively impact meiosis, highlighting the potential consequences of using insect repellent to protect against vector-borne diseases.

The study, published in iScience, was led by Monica Colaiácovo, PhD, professor of genetics at the Blavatnik Institute at Harvard Medical School in Boston. DEET, the main ingredient in many insect repellents, has been shown to have neurological effects, the study explained; however, little is known about DEET’s impact on meiosis, a specific kind of cell division in sexually reproducing organisms. 

Dr. Colaiácovo and her colleagues were inspired to explore the relationship between DEET and meiosis based on how high DEET scored in their initial screens of the impact of various chemicals on meiosis in the model organism C. elegans.

“DEET was one of our top hits in terms of chromosomes not separating properly, so eggs end up with abnormal numbers of chromosomes. In humans, this can cause miscarriage, stillbirth, infertility, and genetic conditions such as Down syndrome," Dr. Colaiácovo told Harvard Medical News in an interview. "We knew we had to look at this carefully."

To better understand the effects of DEET on reproduction, researchers observed the changes in meiosis after worms were exposed to DEET for 24 hours. The team discovered that DEET markedly influenced gene activity, altering the active and inactive genes within a cell.

This altered gene expression resulted in oxidative stress, characterized by an imbalance of free radicals and antioxidants, and distorted the structure of chromosome-forming materials. According to the study, these changes impaired the proper segregation of chromosomes during cell division, resulting in diminished health of egg cells and the subsequent worm embryos.

Although the  findings indicate that DEET can have harmful effects on meiosis in worms, Dr. Colaiácovo noted that more research is needed to determine how DEET impacts human reproductive health. However, she said the study provides a foundation for future research.

“Other groups can take up this work in mice or other animal models and further advance our understanding of what DEET may be doing in human reproductive systems,” said Dr. Colaiácovo. “We can also build on this evidence to flag chemicals of concern for policymakers.”

While DEET has been shown to have potentially harmful effects, Dr. Colaiácovo explained that it remains an effective option for protection against insect bites, which can have immense consequences. When using insect repellents, Dr. Colaiácovo said patients, especially those who are pregnant, should be aware of the potential risks and carefully follow the application instructions.

According to Tiana Dempsey, MD, ABIHM, an integrative doctor who specializes in tick-borne infections, DEET-containing repellents are not the only products that can protect against insect bites. In an article on Lyme disease, Dr. Dempsey suggested repellents made with picaridin, explaining that it has  a better safety profile and is generally more tolerable than DEET.  

Dr. Dempsey also suggested pretreating or spraying clothes with a chemical known as Permethrin, which effectively immobilizes ticks and their ability to attach to and bite the skin. In addition, she instructs her patients to avoid high-risk areas and conduct regular tick checks on themselves, their family, and their animals. 

Whether it's through DEET-containing insect repellent or not, Dr. Colaiácovo said the threat of vector-borne disease is rising and protection against insect bites is essential.

"My family is from South America, where Zika and dengue, for example, are common, and I want to make sure people are not scared away from being careful," she explained. "So-called tropical diseases transmitted by insects are moving into new regions of the world as the climate changes, putting more and more people at risk. The consequences of stopping the use of insect repellents can be very serious."