Citronella, extracted from the leaves of a tropical Asian grass related to lemon grass, has a worldwide reputation as an insect repellent, but I’m not sure that it’s all its cracked up to be. Citronella oil goes into candles, lotions, sprays, soaps, and other products designed to banish pesky bugs. Although it's considered quite safe, the undiluted oil can cause skin irritation, and may increase heart rate in some people.
Does it keep insects away? A study published in the New England Journal of Medicine in 2002 found that products containing citronella oil protected against mosquito bites for under 20 minutes compared to more than five hours for products containing highly concentrated DEET, an effective repellent that I consider toxic and nasty. The least concentrated citronella products didn’t do as good a job as Skin So Soft Bath Oil (a skin moisturizing product that consumers have come to believe has significant repellent effects), which gave a mean of just 9.6 minutes of protection. Incidentally, the researchers also tested wrist bands impregnated with DEET and citronella. None of them worked.
Burning citronella candles may be a better idea than using citronella insect repellents, but I wouldn’t depend on them to keep you bite-free. A Canadian study published in the June, 1996, issue of the Journal of the American Mosquito Control Association compared using three percent citronella candles, five percent citronella incense, an unscented candle and no candle at all in the woodlands of Ontario during several July and August evenings. Those near the citronella candles and incense received fewer bites than those near the unscented candle or in the area with no candle. The reduction attributed to citronella was 42.3 percent and 24.2 percent, respectively. That still leaves a lot of bitten people.
Natural insect repellents containing geraniol appear to be more effective and are my first choice. Neem oil and eucalyptus oil may also work better than citronella. Otherwise, your best bet is to stay indoors at dusk when mosquitoes are feeding, and make sure the screens don’t have any holes.
Andrew Weil, M.D.