an article on insect repellents

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An interesting article I came across... will give you some ideas on insect repellents. The ideal repellent would repel multiple species of biting arthropods; remain effective for at least 8 hours; cause no irritation to the skin or mucous membranes; possess no systemic toxicity; be resistant to abrasion and washoff; and be greaseless and odorless, making it cosmetically appealing. None of the currently available insect repellents meets all these criteria. Efforts to develop such a compound have been hampered by the multiplicity of variables that affect the inherent repellency of any chemical. All the repellents do not share a single mode of action, and different species of insects may react differently to the same repellent. To be effective, an insect repellent must be volatile enough to maintain an effective repellent vapor concentration at the skin surface, but it must not evaporate so rapidly that it quickly loses its

effectiveness. Multiple factors play a role in the effectiveness; these factors include the concentration, frequency, and uniformity of application; the user's activity level and overall attractiveness to blood-sucking arthropods; and the number and species of potentially biting organisms. The effectiveness of any repellent is reduced by abrasion from clothing; evaporation and absorption from the skin surface; wash-off from sweat, rain, or water; a windy environment; and high ambient temperatures. (Each 10°C increase in temperature can lead to as much as a 50% reduction in protection time.) The commercially available insect repellents do not cloak the user in a chemical veil of protection. Any untreated exposed skin can be readily bitten by hungry arthropods. Protection from both the nuisance and the health risks associated with insect bites is best achieved by avoiding infested habitats, wearing protective clothing, and applying adequate insect repellent. Currently, marketed insect repellents fall into 2 categories: manufactured (chemical) repellents and natural (plant-derived) repellents. In general, the chemical repellents have a broader spectrum of efficacy and a greater duration of action than botanical repellents. Thousands of plants have been tested as sources of insect repellents. Although none of the plant-derived chemicals tested to date demonstrate the broad effectiveness and duration of the protection of DEET, a few do show repellent activity. Plants whose essential oils reportedly have repellent activity include citronella, cedar, verbena, pennyroyal, geranium, lavender, pine, cajeput, catnip, cinnamon, rosemary, basil, thyme, allspice, garlic, and peppermint. Unlike synthetic insect repellents, plant-derived insect repellents have been relatively poorly studied. When tested, most of the essential oils yield short-lasting protection, lasting from a few

minutes to as long as 2 hours. Citronella Marketed products include Natrapel, Buzz Away, Herbal Armor, and Green Ban. Oil of citronella is the plant-derived active ingredient found in many natural or herbal insect repellents marketed in the United States. Oil of citronella has a lemony scent and is extracted from the grass plants Cymbopogon nardus and Cymbopogon winterianus. It has been registered for use in the United States since 1948. Conflicting data exist on the efficacy of citronella-based products. This data variation is attributed to differences in study methodology, location, and species of the biting insects tested. One comparative laboratory study demonstrated that marketed citronella-based insect repellents protected against mosquito bites for an average of less than 20 minutes. In general, citronella-based repellents provide considerably shorter protection times than DEET repellents;

therefore, they require more frequent reapplication to maintain their effectiveness. In 1997, the EPA concluded that citronella-based insect repellents must carry the following statement on their labels: "For maximum repellent effectiveness of this product, repeat applications at one hour interval." Citronella products are not intended to be used as tick repellents. Soybean oil The marketed product is called Blocker. Released in the United States in 1997, this natural repellent combines soybean oil, geranium oil, and coconut oil in its formulation. This product has been available in Europe for several years. In tests, this repellent usually provides longer-lasting protection than citronella-based repellents. In some studies, Blocker provided complete protection against mosquito bites for as long as 3.5 hours, and against blackflies for as long as 10 hours. The product is not labeled for use against ticks. Eucalyptus Marketed products include Repel Oil of Eucalyptus Repellent, OFF! Botanical, and Travel Medicine's FiteBite. In Europe, the product is sold as Mosiguard Natural. A derivative, p-menthane-3, 8-diol (PMD), isolated from the oil of the lemon eucalyptus plant has shown promise as an effective natural repellent. This repellent has been popular in China since 1978, is currently available in Europe, and was brought to the US market in 2002. A 30% PMD preparation appears to provide protection comparable to 20% DEET but requires more frequent reapplication to maintain the same level of protection. PMD-based repellents show low toxicity, but care must be taken to keep them out of the eyes because PMD can cause significant eye irritation. In April 2005, the CDC added PMD to its list of approved repellents, joining DEET and picaridin-based repellents

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