Natural Bug Sprays: How Effective Are They?
By Kimberly Beauchamp, ND
Healthnotes Newswire (August 25, 2005)—Topical application of essential oils derived from clove (Syzygium aromaticum), citronella (Cymbopogon nardus), patchouli (Pogostemon cablin), or makaen (Zanthoxylum limonella) may repel Aedes aegypti mosquitoes for up to two hours, reports Phytotherapy Research (2005;19:303–9).
Along with the itching and discomfort that mosquito bites can cause, they may also transmit many serious diseases, such as West Nile virus, malaria, and eastern equine encephalitis (EEE). To reduce the risk of being bitten by mosquitoes, the Centers for Disease Control recommends using insect repellents containing Environmental Protection Agency–registered active ingredients including DEET (N,N-diethyl-m-toluamide) in Deep Woods Off!, picaridin (KBR 3023) in Cutter Advanced, or oil of lemon eucalyptus (p-menthane 3,8-diol or PMD) in Practical Nature’s Tick and Bug Repellent.
As chemical repellents carry the risk of side effects, interest in nontoxic alternatives to chemical insect repellents is increasing, and more studies are investigating the use of plant extracts for warding off mosquitoes. The new study compared the mosquito-repelling activity of 38 different essential oils. Among the oils tested were citronella, clove, sweet basil (Ocimum basilicum), cedar (Cedrus deodara), peppermint (Mentha piperita), garlic (Allium sativum), patchouli, and makaen.
Three participants volunteered to expose a 3 by 10 cm area of forearm to 250 non-infected Aedes aegypti mosquitoes (a vector for yellow fever and dengue fever) after having applied 0.1 ml of one of the essential oils.
Each of the oils was tested at concentrations of 10, 50, and 100% (undiluted). The treated arm was exposed for 1-minute intervals every 30 minutes until two bites had occurred. After this, the arm was exposed once more to confirm that the repellency had failed. Complete repellency times were derived from the time it took for one bite to occur. The four oils with the longest protection times were then tested against the mosquito species Anopheles dirus (vector for malaria) and Culex quinquefasciatus (vector for West Nile virus).
Of the 38 oils tested, the undiluted oils of clove, patchouli, citronella, and makaen provided two hours of complete repellency against Aedes species mosquitoes. Clove oil was the most effective against all mosquito species, providing up to four hours of protection against culex mosquitoes. At a lower concentration (50%), clove oil provided significant protection for at least two hours from culex and anopheles mosquitoes.
As of August 2005, there have been over 1,500 cases of West Nile virus and 74 deaths attributable to the disease in the United States. While the chance of an individual mosquito bite transmitting West Nile virus is very low, common sense precautions should be taken to avoid being bitten. The mosquito that transmits West Nile virus is most active between dusk and dawn. Avoiding outdoor activity during these hours, wearing light-colored clothing, and applying insect repellents reduce the chance of getting mosquito bites.
The new study suggests that the essential oils of clove, patchouli, makaen, and citronella may be safer alternatives to chemical repellents for warding off mosquitoes. DEET has the potential to cause skin blisters, rashes, and eye irritation. Long-term exposure to DEET may cause fatigue, disorientation, mood swings, and brain cell death. Children are particularly vulnerable to the effects of this and other chemicals; therefore, DEET-based products should not be used on children, especially those less than two years old. Picaridin may be a good alternative to DEET, as it ranges from slightly toxic to practically nontoxic in safety analyses. It has been used in Europe, Asia, Latin America, and Australia for many years and is now available in the United States.
Two recent studies have shown that oil of lemon eucalyptus provides mosquito protection comparable to that of DEET-based products. Oil of lemon eucalyptus appears safe for use on infants and children; however, it is an eye irritant and care should be taken to avoid contact with the eyes.
Kimberly Beauchamp, ND, received her bachelor’s degree from the University of Rhode Island and her Doctorate of Naturopathic Medicine from Bastyr University in Kenmore, WA. She is a co-founder and practicing physician at South County Naturopaths, Inc., in Wakefield, RI. Dr. Beauchamp teaches holistic medicine classes and provides consultations focusing on detoxification and whole-foods nutrition.
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