There is a long history of using bug sprays containing repellents to prevent mosquito bites. What works? Many new products have become available in the last 10 years. Repellents with the best track records include the following: DEET, Picaridin, IR3535, and oil of lemon eucalyptus (PMD). The three non-DEET compounds each seem to work as well as or nearly as well as DEET when they are used at higher concentrations (20%). Each of these and other products (Avon Skin-So-Soft; plant-based essential oils) will be discussed in more detail below.
The Centers for Disease Control and the Environmental Protection Agency have assessed test results for the 4 compounds listed above and concluded that they are effective. For more information see these websites:
Since there are lots of types of products, lots of species of mosquitoes, and lots of things that affect how well repellents last or work, analyzing these chemicals is complicated. Many chemicals or products have been tested both in the lab (against 1 or more species) and in more realistic situations outdoors (field testing). Very few repellents have been tested across the whole US against the full range of species that bite humans (an exception is DEET).
For the general public, factors to consider when purchasing a repellent include the amount of time you expect to be exposed to mosquitoes, the intensity of the biting pressure, temperature (which might increase sweat), and your tolerance for the types of chemicals available. The type of mosquitoes in an area will also affect the performance of the different categories of repellents. For travelers outside the USA, you should look at CDC’s webpage for additional recommendations.
Check the concentration. Bug sprays vary in the concentration of the ingredients that repel mosquitoes. In general, higher concentrations are expected to last longer before reapplication is needed. Lower concentrations (5-10%) may be fine when the period of exposure to mosquitoes will be 1-3 hr. In areas of intense mosquito activity, higher concentrations (20% and above) may be needed for adequate protection.
Check the label. Companies that market mosquito repellents frequently change the active ingredients while using the same product name. So last year’s MosquitoRepeller (which contained 10% citronella) may become this year’s MosquitoRepeller (no citronella but 20% picaridin). If you feel strongly about certain chemicals, you should pay attention to the labels.
The most widely available and commonly used repellent is a compound called DEET (N,N-diethyl-meta-toluamide). Products containing DEET are intended to be applied to the skin. Studies indicate that repellents containing DEET at concentrations >20% provide the longest periods of protection against mosquito bites but even low (5-10%) concentrations protect for 1-3 hours.
Slow release formulations of DEET are available (Xue et al. 2007). In these products, a lower concentration of DEET is used while maintaining a long period of protection. For example, a product called 3M Ultrathon (34-36% DEET in a lotion form) has been shown to be as effective as 75% DEET in alcohol, providing 12 hours of protection. Ultrathon aerosol sprays are also available. Sawyer produces a controlled release 20% lotion that provides repellency equal to that of 50% DEET in alcohol.
A newer twist on the use of DEET is the production of wristbands impregated with this compound. One study has shown a reduction in mosquito landing rates when these wristbands were worn (Jensen et al. 2000) while a second study showed no effect of these products (Fradin and Day 2002). Because the wristbands would protect only the immediate area around them, it isn’t surprising that they weren’t very reliable.
The Centers for Disease Control has a useful discussion of repellents http://wwwn.cdc.gov/travel/yellowBookCh2-InsectsArthropods.aspx
Colorado State University has a good summary of repellents
Picaridin (chemical name, 2-(2-hydroxyethyl)-1-piperidinecarboxylic acid 1-methylpropyl ester) is a colorless, nearly odorless liquid active ingredient that is recommended by the Centers for Disease Control and Prevention (CDC) as an alternative to DEET. Picaridin is available in Cutter™ and OFF™ products.
Lab and field studies of products containing picaridin (10-20%) indicate good protection with this compound (Barnard and Xue 2004, Barnard et al. 2002; Naucke et al. 2007; a summary of 14 trials can be found in Frances 2007). Products with lower concentrations (7.5%) are also on the market, and these may need field testing.
IR3535 is recommended by the Centers for Disease Control and Prevention (CDC) as an alternative to DEET. IR3535 is a synthetic insect repellent structurally similar to a natural amino acid, beta-alanine and is classified as a biopesticide by the EPA. This compound has been used as a mosquito repellent in Europe and Asia for 10-20 years (Marchio 1996) and was approved by the U.S. EPA in 1999. IR3535 is currently available in the Avon Skin-so-soft line of mosquito repellents (see below).
Pucetti (2007) summarizes the results of 13 laboratory and field trials. In two recent field studies, an IR3535 containing repellent provided good protection (Naucke et al. 2007, Thavara et al. 2001). A lab study using Avon Expedition insect repellent, 20% IR3535, resulted in protection similar to 20% DEET (Cilek et al. 2004). However, in other laboratory trials, protection was short-lived, ranging between 10 and 60 minutes (Fradin and Day 2002). This study used a product containing a concentration of 7.5% IR3535 (Avon Skin so soft Bug guard plus 7.5%). Similarly Barnard and Xue (2004) and Barnard et al. (2002) reported short periods of protection (2 hours) for 7.5% IR3535 in their lab studies.
Lemon Eucalyptus (PMD)
Plant-derived repellents can provide good protection against mosquito bites. Those based on lemon eucalyptus provide the longest protection (6-8 hr).
Oil of lemon eucalyptus-based repellents include Repel Lemon Eucalyptus Insect Repellent (20%), and SC Johnson OFF Botanicals (10%). The active ingredient in these repellents is para-menthane3,8-diol (PMD), a chemical that can be extracted from the plant or synthesized. Field studies have shown that 20% PMD provided protection that was equal to 20% DEET but the 10% formulation was not as effective (Carroll and Loye 2006). In laboratory and field studies, the 20% formulations provided protection for 6-8 hr (Barnard and Xue 2004, Carroll and Loye 2006).
Soybean oil, Geraniol, or Citronella
Citronella-based products were not effective in laboratory trials. Geraniol-or soybean-oil based products have not been thoroughly tested.
A product containing geraniol (25%, MosquitoSafe) provided 2-4 hr protection in a laboratory study (Barnard and Xue 2004). Oil of citronella contains geraniol as well as citronellal. Field trials have not been published.
Several different citronella-based repellents (5-10%), provided protection for 20 minutes or less in 1 laboratory study (Fradin and Day 2002) and 0.5-5 hr in a second trial (Barnard and Xue 2004). A wristband with 25% citronella failed to prevent bites (Fradin and Day 2002).
Soybean oil-based repellents (Bite Blocker for Kids, 2%) provided 5-8 hrs of protection in one laboratory study (Barnard and Xue 2004) but only 16-195 minutes of protection (average of 1.5 hr) in another laboratory study (Fradin and Day 2002). Different mosquito species were tested in these trials. Field trials have not been published.
Many new products combine several elements, including some of the plant-based chemicals listed above as well as other essential oils. Testing of these products will be discussed below (see products containing essential oils).
Repellents based on other essential plant oils
The following discussion is based on a review by Xue et al. (2007). Botanical insect repellents contain essential plant oils as their active ingredient. A few examples are oils of peppermint, cinnamon, cedar, lemongrass, rosemary, thyme, lavender, catnip and sage. The only essential oils that are registered as repellents by the EPA are oil of citronella and oil of lemon eucalyptus (PMD). EPA requires that registered compounds have demonstrated repellency in lab and field trials. Other essential oils or combinations of these oils are often marketed as mosquito repellents but have not undergone scrutiny by EPA. They are listed as exempt from regulation because there are no safety concerns about these “natural” oils and there has been no requirement that these products demonstrate efficacy. This may change, as EPA is considering whether the public health aspect of repellents is important enough that all products will have to demonstrate that they actually work to repel mosquitoes in the field before they can advertise that they do.
A few products and compounds have undergone some testing. Barnard and Xue (2004) reported that Neem Aura, GonE!, SunSwat, and Bygone all protected for only 0-15 minutes. Bear in mind that the formulations for these brands may have changed since the tests were carried out. In another study, the mosquito repellent activity of 38 essential oils from plants at three concentrations was screened against the mosquito Aedes aegypti under laboratory conditions. The undiluted oils of citronella, patchuli, clove and Zanthoxylum limonella (makaen) provided 2 h of complete repellency. From these initial results, three concentrations (10%, 50% and undiluted) of citronella, patchouli, clove and makaen were selected for repellency tests against Culex quinquefasciatus and Anopheles dirus. As expected, the undiluted oil showed the highest protection in each case. Clove oil gave the longest duration of 100% repellency (2-4 h) against all three species of mosquito. However, clove oil should not be applied undiluted to skin as a homemade repellent as it often causes skin rashes and irritation. This is also true of several other essential oils (e.g. cinnamon, thyme).
In 2001, Catnip oil was reported to repel mosquitoes 10 times better than DEET. Subsequent tests of this claim have shown some repellency for catnip oil and its component nepetalactone (Zhu et al. 2006). However, these laboratory tests have not shown that catnip oil works as well as DEET. There were also unusually strong differences in protection time between the mosquito species tested, ranging from no protection to 4 hours (Webb and Russell 2007, Chauhan et al. 2005, Bernier et al. 2005).
Vanilla, a common kitchen flavoring, has been suggested by members of the general public as a possible repellent. Two published studies demonstrated minimal to no repellent activity of vanillin, the primary component of the extract of the vanilla bean (Khan et al. 1977; Tawatsin et al. 2001) and this is supported by informal testing by my laboratory and correspondents. However, the two published studies indicated that addition of vanillin to DEET or to other repellents increased the efficacy against some mosquitoes (Khan et al. 1977; Tawatsin et al. 2001). Extracts of vanilla plants also have been tested for the ability to kill mosquito larvae directly (insecticidal rather than repellent function).
Garlic oil may be an alternative mosquito repellent for humans but testing is limited. In a field study conducted in India, a preparation made of 1 percent garlic oil, petroleum jelly and beeswax that was rubbed on the arms and legs of study subjects was found to be effective in preventing mosquito bites for up to eight hours (Bhuyan et al. 1974). See also Home Remedies for studies of the ingestion of garlic.
Since then, Avon® has produced a line of Skin-So-Soft products specifically designed to repel mosquitoes and these currently incorporate IR3535 or picaridin (see the sections above on these two chemicals. In 2008, the line of mosquito repellents included:
SKIN SO SOFT BUG GUARD Plus PICARIDIN Aerosol Spray with 10% Picaridin
SKIN SO SOFT Bug Guard Plus IR3535® EXPEDITION™ SPF 30 Aerosol Spray with 20% IR3535
SKIN SO SOFT BUG GUARD PLUS IR3535® Gentle Breeze SPF 30 Sunscreen Lotion
With 7.5% IR3535
These products were tested by Cilek and colleagues (2004) in cage studies against two species of mosquitoes. In general, the length of protection was similar to that for DEET preparations of similar concentration.
Fradin and Day (2002) tested an older version of Skin-so-soft Bug guard® (with 0.1% citronella) which is no longer available, and Skin-so-soft Moisturizing Suncare® (0.5% citronella, again no longer available. In this study, they also tested Skin-so-soft bath oil®(active ingredient unknown). These products provided protection for an average of 10-15 minutes (range of 1-30 minutes for all volunteers).
Permethrin (Permanone; 0.5%) should not be applied directly to the skin or to inner clothing (socks or underwear). You can spray your outer clothing with this product but be sure to allow enough time for them to dry completely before you wear them. If I am working in the field, I usually spray my clothes the day before I leave. Do this outside-not in the house/apartment. Spray each side of the fabric until moistened, and be sure to spray the openings to the clothing. Then, hang the clothes out to dry.
You can now purchase repellent clothing that incorporates permethrin or a related chemical. For these products, the repellent persists through repeated washings. Similar technology is used by the US Military.
From the Centers for Disease Control and Prevention: “Travelers should be advised that permethrin-containing repellents (e.g., Permanone) are recommended for use on clothing, shoes, bed nets, and camping gear, and are registered by the U.S. Environmental Protection Agency (EPA) for this use. Permethrin is highly effective both as an insecticide and as a repellent for ticks, mosquitoes, and other arthropods. Clothing treated according to label instructions should provide protection for up to 2 weeks and through several machine washings before re-treatment is required. Clothing pre-treated with permethrin is commercially available and should be used and washed according to the manufacturer’s instructions. There appears to be little potential for toxicity from permethrin-treated clothing. Permethrin-treated clothing should be supplemented with topically applied repellents to protect exposed skin.”
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Bernier U. R., Furman K.D., Kline D. L. Allan S.A., Barnard D.R. 2005. Comparison of contact and spatial repellency of catnip oil and N,N-Diethyl-3-methylbenzamide (DEET) against mosquitoes. Journal of Medical Entomology 42:306-311.
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