Everything you need to know about bug spray ingredients

Nothing kills our chill-out-in-nature vibe faster than becoming an all-you-can-eat buffet for mosquitos, ticks and other bloodsuckers. And beyond the maddening itchiness, insect bites can pass along serious disease too—even if you’re not somewhere tropical.

“While Canada does not have local transmission of insect-borne killers like malaria and dengue, there are infectious diseases spread by insects here that can ruin your summer,” says Dr. David Fisman, professor of epidemiology at the Dalla Lana School of Public Health, University of Toronto, pointing to West Nile virus (from infected mosquitoes) and Lyme disease (via deer ticks).

So how can you get bugs to buzz off without dousing your family's skin in irritating chemicals? Here’s what you should know about insect repellents—the good, the bad and the useless.

DEET Invented for the US military in the '40s, DEET still ranks most effective. In a study testing 16 bug repellents on particularly game volunteers, published in 2002 in the New England Journal of Medicine (NEJM), DEET-based repellents fared best, giving “complete protection for the longest duration.” DEET’s side effects—some minor (skin/eye irritation), others scary (seizures and other neurological symptoms)—make a lot of people leery. But serious reactions are very rare; they’re typically linked to repeatedly applying way too much or ingesting it. Even the Environmental Working Group says, “DEET is generally safer than many people assume.”

Picaridin (A.K.A. icaridin) Harder to find than DEET but considered a solid alternative, picaridin is a synthetic ingredient approved by Health Canada in 2012. It’s similar to a compound found in the black pepper plant. Picaridin is thought to be almost as potent as DEET, without the same pitfalls: it doesn’t irritate the skin and eyes, it’s not stinky and it doesn’t come with a “potentially toxic” rep. In the US, where it’s been sold for longer than in Canada, a recent study found no reported cases of major side effects.

Oil of lemon eucalyptus If you want something botanically based, oil of lemon eucalyptus is pretty much the only option with serious scientific credibility. The ingredient’s active compound is p-menthane-3,8-diol (PMD); look for it on the label. Don’t confuse this ingredient with unrefined lemon eucalyptus essential oil—it’s not the same thing. A new study of 11 bug repellents, published this year in the Journal of Insect Science, ranked sprays with DEET and PMD as the most effective at keeping mosquitos at bay. Other research has found that oil of lemon eucalyptus is on par with low-concentration DEET (in other words, it doesn’t last as long as high-concentration DEET, but it still offers protection).

Other plant oils (eg., soybean and citronella) Despite being pitched as safer-for-you bug repellents, other plant oils provide protection that's murky at best. Some might do the job for a short while (sometimes repelling for mere minutes)—if they work at all. An old NEJM study found that a soybean oil–based product curbed bites for about 1.5 hours. But a more recent study in the Journal of Insect Science observed that two natural bug sprays (one with soybean oil plus geraniol, and one with citronella) had “little or no” effect on deterring mosquitos. So if you’re relying on these ingredients? Use them where there’s no risk of catching anything serious.

Read more: The best ways to protect your kids from bug bites this summer Ask Dr. Dina: Are insect repellents with DEET safe for kids? Myths and facts about mosquito bites