The Best Mosquito Repellent

You know I talk a lot about the killers IN our food – but what happens when we ARE the food. Today, we ponder the pros and cons of repelling mosquitoes with Deet. 

The most dangerous animal in the world isn’t the great white, or the king cobra, or lions and tigers and bears. In fact, only about 10 people die in shark attacks every year. Coming in #2 as most dangerous—fellow human beings. But the worst? Mosquitoes.

Literally billions of people are at risk of contracting dengue fever from mosquitoes, and hundreds of thousands die from mosquito-borne malaria every year. New threats like Zika continue to pose a global public health threat, such that the World Health Organization suggested delaying pregnancy in Zika-affected areas around the world. What’s the best mosquito repellent to wear?

There are products like permethrin, a product originally derived from chrysanthemums, interestingly, that can be applied to clothes. But what about the repellents you actually put on your skin? DEET is the repellent to beat, considered the gold standard of protection when it’s crucial not to get bitten. It was developed back in the 1940s for use by the military. It’s long been considered the first-line mosquito repellent. Effectiveness-wise, 20 to 50 percent DEET repellents provide up to several hours of protection. That’s rubbed on the skin, though.

DEET-impregnated wristbands don’t work, repelling mosquitoes only from areas covered by the band––which I guess you could say about non-DEET-impregnated wristbands. DEET or citronella wristbands have been clocked at working more broadly for only 12 to 18 seconds. Safety-wise, DEET is considered safe even in the second and third trimesters of pregnancy and in children, as long as they’re older than two months. Now, it should be noted that DEET can damage plastics and synthetic materials; therefore, care should be taken when it is used around plastic watches, eyeglasses, and synthetic fabrics. Nylon is okay, but it’s been found to damage spandex, rayon, acetate, and pigmented leather, in addition to plastic and vinyl.

DEET is absorbed through your skin into your bloodstream, but it’s cleared from your system within a few hours. Does it have any adverse effects? DEET is probably far less toxic than many people believe. DEET has a remarkable safety profile after now more than a half century of use and billions of applications. Fewer than 50 cases of serious toxic effects have been documented in the medical literature since 1960, and most of them resolved. Most reported cases of adverse or lethal events involved overuse or incorrect use of the product. Incorrect use as in chugging it to commit suicide.

What’s a correct usage? Read and follow all directions on the product label. Only apply to intact non-irritated skin. Do not apply near eyes and mouth and only sparingly around ears. That’s to avoid accidental eye exposure or ingestion. It can be applied to the face, but don’t spray it on your face. Spray it on your hands and then you can dab it on, but still avoid the eyes and mouth. Apply it to children so they don’t swallow any. Just use enough to cover exposed skin or on the outside of clothing, not underneath. And, then once you’re back inside, wash it off with soap and water, and wash any treated clothing. If you do have a reaction, stop using it, wash it off, call your local poison control center, and if you go to your doctor, bring the bottle.

So, which mosquito repellent works best? In head-to-head tests, DEET crushed it. But this was in reference to a study published about 20 years ago. Anything new on the market that won’t melt your eyeglasses? We’ll find out, next.

DEET has been considered the most effective mosquito repellent. Unquestionably, read this editorial in The Journal of Family Practice, it should be the only mosquito repellent recommended by physicians, with no other repellent coming close. Given the dramatic efficacy, it’s hard to conceive that any other repellent would ever beat it. However, there are some rare reports of severe reactions to DEET, not to mention the fact that it can melt plastics, like eyeglass frames and cellphone components, and many consumers find the odor and sensation on the skin unpleasant. Enter picaridin. Overall, studies have shown little difference between DEET and picaridin applied at the same dosage, with some evidence pointing to a superior persistence for picaridin––all without the irritancy, odor, and melted glasses.

No wonder it got Consumer Reports’ pick for the best overall insect repellent. Note that concentration matters. Their 20 percent picaridin product topped the list, but at 5 percent it was one of their worst-performing products. Any toxicity? Adverse effects, when occurring, primarily manifested as eye irritation/redness, vomiting, and oral irritation. But, of course, you’re not supposed to eat it or spray it in your eyes. But even unintentional ingestion was associated only with relatively minor toxicity.

What about the electronic mosquito-repellent gizmos? There were 10 studies done, and all 10 found that there was no difference in the number of mosquitoes landing on people with or without the gizmos, and experiments out in the field confirm: no effect on preventing mosquito bites.

Picaridin was roughly based on a black pepper compound, but, like DEET, is a synthetic chemical. Are there any natural repellents? Of course, just because something is natural doesn’t mean it’s necessarily safe. Strychnine is a natural product of the strychnine tree, and ricin from castor beans is 10,000 times deadlier still. In fact, the top 10 most toxic poisons are all natural.

But, let’s look at the mosquito-repellent effects of about 20 essential oils, compared to a placebo control group, and to DEET. The asterisks point to the significant results, so here’s a cleaner peek. Only five had any lasting effect at all. Peppermint and lemongrass oil were effective for 30 minutes. Spearmint and garlic oil started working but didn’t even last that long. Cinnamon oil, though, reduced mosquito attraction for one and a half hours. The remaining essential oils had no significant effect on mosquito attraction at any time point, and this includes citronella.

Citronella was the most widely-used repellent before DEET was invented, and it is still used today in many formulations, despite inferior efficacy. At lower concentrations, it may only last a few minutes, and at higher concentrations, citronella can cause skin irritation. Compared to a complete protection time of six hours for DEET, citronella may only last 10 1/2 minutes. Therefore, citronella may be acceptable for brief exposure to nuisance mosquitoes, but it is not advised for protection if you really can’t afford to get bit. Essential oils, read this Family Medicine Journal editorial, have no effectiveness, and are not recommended. But that was before we learned about lemon eucalyptus, the only plant-based repellent recommended by the CDC––though it should not be used by pregnant women or children younger than three years of age.

Consumer Reports listed it as one of their top three picks, warding off mosquitoes and ticks for at least seven hours. All the other botanical products they tested failed. But 40 percent lemon eucalyptus was shown to prevent bites for 4 to 7 hours after application for aggressive species of mosquitoes, and for greater than 12 hours for less aggressive mosquitoes––a period of prevention greater than at least a 10 percent DEET repellent.