Citronella is an oil distilled from grasses. It has a lemony or citrusy fragrance that masks other odors, effectively confusing odor-tracking insects. So, citronella will ward off pests, not kill them -- it's used in diffusers and wax candles to clear the air of pesky biting bugs when people want to enjoy some time in the great outdoors. Citronella candles get mixed reviews. It helps to understand how they work before deploying them.

Ancient Trick for an Old Problem

Releasing the volatile compounds in plants is an ancient practice still in use in developing countries and among those in search of more "natural" insect repellants. Citronella oil, as is the case with a number of plants containing chemicals that emit an odor when bruised or broken, wards off multiple pests. These include the female Aedes aegypti mosquito, the culprit responsible for all those itchy bumps you acquired at your last backyard barbecue. When the oil is infused in a wax candle, the scent is released over time in a cloud of smoke the mosquito would prefer to avoid. She's still out there, circling and hungry, but at least she's not fastened to your arm.

The Bugs in the Citronella Solution

That's the good news. The caveat is that you have to be immersed in the smoke to hide your savory presence from tiny predators. Insufficient smoke to create a safe zone large enough to protect you means you are vulnerable. So does sitting outside the mosquito-free refuge. When the wind blows, the smoke dissipates too quickly to provide any protection. One candle for a picnic table is going to keep the platter of fried chicken safe, but it won't do much for your bare ankles. A study published in the Malaria Journal found that citronella candles offer only about a 50 percent reduction in mosquito bites. Another study, published in the Journal of the American Mosquito Control Association, assigned reduction in bites to 42.3 percent with adequate coverage by typical 3 percent citronella oil candles. Those results are better than nothing, but still pretty itchy.

How Mosquitoes Find You

Wearing or not wearing certain perfume, bathing or not bathing with scented soaps, eating or not eating things made with sugar -- none of these give you a magic anti-mosquito amulet. The Aedes mosquito is drawn to higher than normal concentrations of carbon dioxide in the atmosphere -- your exhalations. They can find that scent from as far as 100 feet away. Any additional scents -- perfumes, sweat -- just compound the irresistible appeal. The tantalizing view of your bare skin -- or lightly clad skin -- is a proboscis-enticing view at about 30 feet. Body heat is another heads-up to a hungry mosquito; you really don't stand a chance when it's dinner time. But when the mosquito's sensors are muddled and can't find you, it's possible to escape notice long enough to finish your cheeseburger. The hitch is, you are breathing in citronella smoke -- science has not yet determined the effects of citronella vapor on the human body. Moderate amounts of the oil don't seem to be harmful; the molecules break down and are excreted. But prolonged exposure to the candle smoke hasn't been tested.

Don't Become Dinner

So, what can you do to avoid cowering indoors during mosquito season? You do have options -- some less risky than others. Go ahead and use your citronella candles, but not as a sole defense. Get rid of all standing water to remove favorite mosquito breeding grounds. Neutral and light-colored clothing won't advertise your presence so glaringly, and leaving off the perfume sends less of an olfactory invitation. Set up an oscillating fan to cover the area -- mosquitoes won't exhaust themselves battling a gale to get to you. And consider a lotion or spray containing DEET if you are in a malaria or dengue infested region.