Insect-borne diseases stimulate new interest in natural repellents.
Antagonism between man and biting insects is ancient. Those who have stored sweaters in a family cedar chest, however, swear by the insect-repellent qualities of cedar oil. Concerns about effects of chemical insecticides such as DEET, worries about insect-borne illnesses and recent explosions in the bedbug populations of Western nations have revived interest in older, more naturally based substances that repel bugs without harming humans, among them cedar oil. Does this Spark an idea?
History
Ancient peoples relied on natural plants, crushed to release volatile oils or burned, to keep insects at bay. Elizabethan and Puritan "strewing herbs" covered floors to repel insects. In response to 1980s and 1990s concerns about West Nile virus, urban legend-debunker Snopes.com published a long list of ineffective insect-repellers, including Mexican vanilla, brewer's yeast and B vitamins. Modern reviews of old herbal practices identify active oils in different varieties of cedar, emphasizing dangers of ingesting cedar and the possible role of cedar oil in inducing abortion; but only one cedar, West Indian aromatic, is cited as a possible insecticide.
Scientific Study
In 2002, the National Toxicology Program of the National Institutes of Health examined possible toxic effects of cedar wood and chemical components on animals and humans. Criteria included human and nonhuman toxicity, for both internal consumption and external application. Impeti for studies included industrial cedar products, increasing use of cedar in insecticides, and questions about the suitability of substituting cedar oil for napthalene in moth repellents. Cedars analyzed were Western Red Texas and Virginia cedars, all of which were chemically distinct. The three oils were judged nontoxic to humans and to the warmblooded animals on which further studies were based.
Commercial Applications
Most recent commercial insecticides and insect repellents involving cedar oil have been focused on the bedbug population plaguing Western European and U.S. stores and public accommodations as well as homes. Parental concerns about the effects of powerful chemicals on children and pets and the more general "green" reaction to chemical toxicity have fueled this logical revisiting of possible herbal remedies. Even optimistic reports of bedbug-targeted products must, however, recognize a distinct limitation to cedar oil. Sprayed directly on bedbugs, it kills them in less than a day. Left as a residue on bugs removed from the original site, it eventually kills them, within a couple of weeks. It appears, however, that spray in the area of bugs has no effect.
The Verdict
As is often noted at the end of clinical studies, further research is needed. As a repellent for insects that feed on fabric, cedar oil does an excellent job. As a repellent for insects that feed on warm-blooded mammals, the lack of harm cedar oil does to humans and pets may also extend to a lack of harm to insects except in suffocating, directly-applied amounts. Cedar oil may still be a green ingredient whose full potential remains to be understood and activated.
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