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John Whyte, M.D., MPH Headshot

Does Bug Spray Do More Harm Than Good?

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The weather has been pretty gorgeous lately, and I bet you've been heading outside most chances you get. You've got your hat and sunglasses on when all of a sudden -- slap! -- oh hello mosquito!

The thought of stepping out only to become a blood buffet for these insects is almost enough to cancel that outdoor barbecue. Even worse, wear smelly socks (as one recent report suggests) and the mosquitoes will zoom towards you like a pack of flies to Lady Gaga's meat costume. Every year, about a third of us will rub on five to seven million pounds of repellent in hopes of fending off hungry mosquitoes. And for good reason! There are, after all, mosquito-transmitted diseases to worry about: West Nile virus, encephalitis and malaria, to name a few. Protecting yourself from bites is important, but if the repellent annoys the mosquito, have you ever wondered if it can also hurt you?

Let's start with the grand-daddy of them all: DEET-based repellents. DEET (N,N-Diethyl-meta-toluamide) has been around for over 50 years and has been applied on human skin more than five billion times. It's a common active ingredient in many mosquito repellents. There's been some concern over potential toxicity; the Environmental Protection Agency (EPA) evaluated DEET's potential toxicity based on the assumption that it's something most of us would only need to use occasionally for a short period of time.

The EPA placed DEET in Category 3, "slightly toxic," the second lowest of four categories. The EPA does not believe occasional use presents a health concern. If, on the other hand, your daily job happens to be park ranger in the swampy Everglades, you live in a malaria-infested area or dabble in jungle warfare, using DEET frequently will increase your risk of side effects. What are the side effects? The serious one is the risk of damage to the brain and other organs. DEET is absorbed through the skin and enters the bloodstream fairly quickly -- even more quickly if you combine it with sunscreen containing oxybenzone. Most of the time, if you have a reaction, it's some skin irritation. Perhaps most troubling, its strong odor doesn't always mesh well with barbecue brisket and beer.

Icaridin (marketed as Saltidin) came along as an alternative to DEET. By contrast, it's odorless, colorless, less likely to produce skin irritation and does not have the risk of hurting your brain cells. It works by blocking the mosquito's ability to find you. Like DEET, the higher the product concentration, the longer the protection time. A 20 percent solution gives good protection.

For you fashionistas, mesh clothing and wrist bands pre-treated with DEET are also available. Unless you're worried about just bites to the wrist, you might want to pass; a 2002 New England Journal of Medicine study showed that these wrist bands protected users for about 18 seconds, hardly long enough to even see if your outfit matches.

For anyone considering more natural or plant-derived ingredients, various botanical agents have also been evaluated as a potential way to repeal mosquitos and other insects. Examples include cedarwood, soybean oil, citronella and oil of lemon eucalyptus. Among these, soybean oil and oil of lemon eucalyptus seem to be the most promising. Soybean oil-based products provide on average 1.5 hours of protection from bites and are non-irritating to the skin. Drawbacks are the strong smell and sticky residue.

Oil of lemon eucalyptus is as effective as low-concentration DEET, non-irritating to the skin, but also with a strong, distinctive smell. Undiluted plant oil extracts from peppermint, basil, rosemary and celery seed have all shown the ability to kill mosquito larvae. However, their ability to repel mosquitoes in their natural plant form has not been reported. So fortressing your house and deck with these plants may not work, but at least you'll have a nice herb garden! I'll be honest: my wife has tried these plants, and I still have mosquito bites.

Have you seen those electronic devices that emit a low-frequency sound claimed to be intolerable to mosquitoes? Too bad scientists say they don't work! Apparently, mosquitos are tougher than they look and can tolerate it!

Other electronic gadgets like bug zappers can kill bugs but are not specific for mosquitoes. These devices typically have UV lamps that draw insects to them before the electricity turns them into popcorn. However, mosquitoes are more drawn to carbon monoxide than UV light, so these devices often end up killing more harmless or even beneficial insects. As an added caution, the cloud of aerosolized bug parts scattered by the machine (up to 6 feet away) can themselves contain bacteria or viruses. Squeamish strawberry yogurt fans may not want to know where the natural red food coloring carmine comes from.

On the lower end of technology, mosquito coils have been around for over 100 years. Popular in Asia, Africa and South America, these spiral-shaped coils contain insecticide and are lit like incense, repelling mosquitoes with their smoke. The smoke may not clear your mind, but it could clear out the lawn party. Using one mosquito coil releases the same amount of particulate mass as burning 75 to 137 cigarettes and emits the equivalent amount of formaldehyde (a known carcinogen) as 51 cigarettes. Even with the second hand smoke, coils are just not as exciting to watch as a bug zapper in action.

Some people have suggested taking thiamin (vitamin B1) and garlic as a way to keep mosquitos away, but the data just have not shown that they work. The garlic can, however, keep would-be conversationalists away.

With all these available products, what provides the best mosquito protection? It really depends on personal preference. If you live in an area with lots of mosquitoes, you're outside for hours or you don't want to keep reapplying repellent, then a higher concentration DEET repellent is probably your best bet. On the other hand, if your skin and your nose can't tolerate DEET, or you're concerned about potential side effects, try a repellent containing at least 20 percent icaridin.

More plant-based essential oils may become available in the future, but for now if you want to go the more natural route, oil of lemon eucalyptus and soybean oil repellents are good options. Just be prepared to deal with some sticky residue and smell of the plant oil. These oils also need to be reapplied more frequently to offer the same level of protection as DEET-based products. If all else fails, at least make sure you have clean smelling socks.

http://www.epa.gov/pesticides/factsheets/chemicals/deet.htm

Kline DL, Olfactory responses and field attraction of mosquitoes to volatiles from Limburger cheese and human foot odor. J Vector Ecol. 1998 Dec;23(2):186-94.

Fradin, MS, and JF Day. "Comparative efficacy of insect repellents against mosquito bites." New England Journal of Medicine 2002; 347: 13-8.

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