Repellents: What Really Works?
This article was originally published on September 11, 2006 and expired on September 18, 2006. It is provided here for archival purposes and may contain dated information.
The warm summer days occurring throughout Illinois means that people are outdoors and, in general, wearing minimal clothing, which increases the possibility of getting bit by mosquitoes. The Illinois Department of Public Health has recently issued news releases warning of the increased incidence of West Nile virus in Illinois (http://www.idph.state.il.us/public/press06/8.24.06wnv.htm).
As of August 29th, there were 25 human cases, and the first fatality of the year occurred August 23. The concerns associated with West Nile virus, which is vectored by several mosquito species (including the northern house mosquito, Culex pipiens) warrant protection to avoid mosquito bites. Most active at dawn and dusk, mosquitoes are attracted to heat, moisture, carbon dioxide, and dark-colored clothing. Also, females can detect lactic acid and octenol, emitted when an individual sweats. Sweat acts as a kairomone, making it easier for female mosquitoes to locate hosts.
Primary methods to deal with mosquitoes include eliminating breeding sites, controlling larvae, and applying personal repellents. Repellents are materials applied to the skin and/or clothing, depending on the particular repellent, and are supposed to keep mosquitoes from landing on skin and initiating a biting sequence.
DEET (N, N-diethyl toluamide or N, N-diethyl-meta-toluamide), developed in 1946 and available to the public in 1957, has been the product of choice in deterring mosquitoes from biting people because it is very reliable. In fact, no other repellent provides the level of protection against mosquitoes and is as persistent on human skin.
In general, DEET has a good safety record although there may be toxicological issues, primarily related to hypersensitive reactions. Also, DEET repels a broad range of biting arthropods, including ticks, sand flies, chiggers, and deerflies. However, DEET's activity or how it repels insects, especially mosquitoes, is not well understood.
A 30% concentration of DEET provides up to 8 hours of protection, particularly against house mosquitoes. Concentrations between 10% and 35% are sufficient to "ward off" most mosquito species. Besides applying DEET to your skin, you can also apply it to clothing.
It is important to note that DEET should not be used on children under the age of 2, and only DEET concentrations up to 10% should be used on children. Be careful when applying DEET because it damages plastics, as well as watch crystals and eyeglass frames. Avoid using DEET with a sunscreen because the combination may reduce the sunscreen's effectiveness. Products containing DEET include Off and Cutter.
Permethrin is a pyrethroid-based insecticide typically applied to clothing or imbedded into mosquito netting. It does not repel mosquitoes but kills them on contact. It should be applied only to clothing–not skin. Applications to clothing may provide up to 2 weeks of protection from mosquito bites. Permethrin is also effective against ticks, chiggers, and biting flies. Products containing permethrin (at 0.5%) include Repel Permanone and Cutter Outdoorsman Gear Guard.
Essential oils or those compounds derived from plants such as clove, peppermint, geranium, and catnip may repel mosquitoes. Citronella, derived from a lemon-scented grass (Cymbopogon nardus), is commonly used as a repellent in products such as Natrapel and Buzz Away. Also, citronella candles have been promoted as a method to repel mosquitoes. However, volatility impacts the effectiveness of citronella, as well as other essential oils, as repellents. For example, citronella is active as a repellent for only about 30 to 40 minutes. Citronella oil, derived from the geranium species Pelargonium x citrosum, is used as a repellent but lacks persistence in outdoor environments.
Catnip (Nepetia cataria) acts as a repellent. However, pure catnip oil should not be applied directly to the skin, and catnip is active as a repellent for only 3 hours. A substance in tomatoes (Lycopersicon spp.) repels mosquitoes and other insects such as fleas and biting flies.
Although popular, Avon Skin-So-Soft repels mosquitoes for only up to 20 minutes because it is volatile and evaporates quickly, meaning to consistently repel mosquitoes, it must be applied repeatedly. Numerous factors may influence the length of protection or the effect of repellents on mosquitoes, including concentration of the repellent, time of day, temperature, and humidity. Also, characteristics of individuals, such as age, sex, level of activity (related to sweating), and "attractiveness" influences the effectiveness. Several guidelines for using repellents follow:
- Always read the product label before applying any repellent.
- Apply repellents to exposed skin according to label directions.
- Be cautious when applying repellents to children. Do not apply repellents to children's hands.
- Avoid applying repellents to cuts or skin wounds.
- Do not apply repellents directly to the face.
Source: Phil Nixon, Extension Specialist, PAT/Ornamental Household Insects and Raymond A. Cloyd, Extension Specialist, Ornamental Entomology/IPM
Pull date: September 18, 2006