The Deet debate: Is your bug spray putting you at risk?

Bug sprays with Deet offer strong protection against deadly insect-borne illnesses when used properly. Photo / 123rf

Some worry that this active ingredient is toxic. Here’s what we know about its effect on human health.

Q: Everyone says that the Deet in bug spray is awful, but my own research seems to suggest that it’s well-tested and safe. Am I giving myself a little bit of cancer every time I use it?

A: A spritz of a Deet-containing bug spray might smell unpleasant, but when used correctly, Deet’s offensive odour might be its most harmful effect, said Dr Joseph Kennedy, a physician and medical toxicologist at the University of Vermont Medical Centre.

Still, there’s widespread concern that Deet might be potentially toxic or cause cancer, he said, with “so many misperceptions”.

Here is why people think Deet is bad for human health, and what we know about its safety.

How does Deet work?

Scientists aren’t exactly sure how Deet repels insects. But contrary to what many people may think, Deet is not an insecticide, Kennedy said. It doesn’t kill mosquitoes and is not poisonous to them. Instead, it simply deters them, likely with its noxious smell.

“The whole point of smelling unpleasant is you’re not the only one that thinks that,” Kennedy said. “Insects do, too,” he said. That includes other bugs like ticks, fleas and biting flies.

Another theory about how Deet works is that it masks certain human emissions, like carbon dioxide, which insects are normally attracted to, Kennedy said.

Deet doesn’t kill insects; it repels them with its unpleasant smell. Photo / 123RF

Is Deet safe?

Millions of people in the US use Deet-containing products every year, according to the Environmental Protection Agency. Yet between 2007 and 2012, there were only about 2800 reported health incidents involving the chemical, the agency said in its most recent review.

Deet has also been used for about 80 years. If it was toxic or caused cancer, “it would have showed up a long time ago,” said Jeffrey Bloomquist, an insect toxicologist at the University of Florida.

Most incidents the EPA noted were minor, involving skin, eye or respiratory irritation like rashes, watery eyes or wheezing.

“If you get it in your eyes or your mouth, it is really unpleasant,” Kennedy said.

Bloomquist said that Deet-containing products are safe as long as they’re applied correctly – meaning only to exposed skin and not sprayed directly on to the face or broken skin.

And don’t use more than is needed, Bloomquist said, especially with children, who tend to absorb more of the chemical through their skin than adults. He recommended that young children or infants use products with lower concentrations of Deet (a 24% solution should be adequate). And he suggested spraying it on to their clothing rather than directly on to their skin.

If used improperly, such as if someone swallows it or applies too much, Deet can cause severe health effects like seizures, low blood pressure, unco-ordinated movements or death, Kennedy said. But those cases are rare – seizures, for example, occur only once in every 100 million uses, according to the EPA.

It’s also worth noting that some repellents come in high concentrations such as 100% Deet, which is overkill for most people, Bloomquist and Kennedy added.

Little quality research on the relationship between Deet and cancer has been conducted in humans, Bloomquist said. The Centres for Disease Control and Prevention has reported that long-term exposure is not associated with an increase in tumours in rodents, rats or dogs.

And Deet hasn’t been shown to cause harm to pregnant women or their fetuses.

Where did the panic come from?

In the 1980s and 1990s, a few isolated reports of seizures and deaths linked to Deet sparked widespread concern. However, those people hadn’t used Deet as directed.

Between 1960 and 2020, researchers have reported only nine deaths related to Deet poisoning. Of those, four had intentionally swallowed the chemical – and among them, some had also ingested other substances, like alcohol or antidepressants, which could have played a role in their deaths. The other cases included two young children and a baby whose parents had applied Deet every night for weeks or months, and two adults who had applied more Deet than necessary. It’s unclear if the Deet or something else – such as an underlying health condition – played a role.

Deet also sounds a lot like DDT, a toxic insecticide that is now banned. “People mix those two chemicals up,” Kennedy said.

Deet has been used for nearly 80 years with minimal reports of serious health incidents. Photo / 123rf

Does Deet have health benefits?

One major benefit of Deet is its ability to protect against insects that may transmit potentially deadly illnesses like dengue, West Nile or Lyme disease.

“It’s stunningly effective,” Kennedy said.

In a 2022 study, volunteers stuck their Deet-coated arms in a cage of hungry mosquitoes. Those wearing insect repellents containing about 24% DEET were fully protected from insect bites for around five hours. Repellents that contained only essential oils such as citronella or peppermint oil protected them for less than 20 minutes.

When using any chemical, Kennedy said, there are risks and benefits. But the toxic side effects of Deet are far less common than what can occur with insect-borne illnesses, such as an irregular heartbeat caused by Lyme disease or severe anaemia with tick-borne babesiosis, he added.

“These truly life-altering diseases can be prevented with just some basic precaution and application of a repellent,” Kennedy said.

This article originally appeared in The New York Times.

Written by: Isobel Whitcomb

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