Insect Repellents

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Pest Management Fact Sheet #5108

Griffin M. Dill, IPM Professional.

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Enjoying the Maine outdoors often involves facing a number of arthropod pests including ticks, mosquitoes, black flies, midges, and other biting flies. Moving beyond the simple annoyance posed by these pests, serious mosquito-borne diseases such as West Nile Virus (WNV) and Eastern Equine Encephalitis (EEE), as well as the tick-borne Lyme disease can cause serious illness and even death. Insect repellents are an important tool in preventing these diseases while also allowing us to enjoy everything the Maine outdoors has to offer.

Repellents can come in a variety of forms including lotions, wipes, pumps, candles, impregnated cartridges, and pressurized sprays. The effectiveness of repellents depends upon active ingredient, concentration, target species, as well as a host of other secondary factors. This fact sheet provides information that will help you make educated decisions regarding the safe and effective use of insect repellents.

Choosing a Repellent

When heading outdoors, choose a repellent that best fits your needs based on:

  • Length of exposure (How long do you plan on being outside?)
  • When and where you will be (Some pests are more active at specific times and certain places are more likely to have higher pest activity than others.)
  • What you will be doing (Physical activity, temperature, and water exposure can influence the endurance of repellents.)
  • Type of pest present (What types of pests are in the area: mosquitoes, ticks, flies, etc?)
  • Effectiveness of active ingredients (Do you prefer a synthetic repellent or a natural repellent?)
  • Age of user (Caution should be used when selecting repellents for use on children.)

Not all insect repellents are the same. Specific brands use different active ingredients and different concentrations of these ingredients. The following active ingredients have been determined to have varying degrees of effectiveness in repelling biting arthropod pests. The first four repellents (DEET, Picaridin, IR3535, and Oil of Lemon Eucalyptus) are recommended for use by the Centers for Disease Control and Prevention (CDC) based upon their endurance and effectiveness against biting arthropods.

DEET: DEET is the commonly used acronym for the chemical N, N-diethyl-meta-toluamide. It has been extensively used as a highly effective mosquito repellent and also works well on ticks, fleas, black flies, and biting midges (no-see-ums). DEET can be found in concentrations ranging from 4-100%. However, studies indicate that concentrations greater than 30% do not provide added protection and have resulted in skin reactions and eye irritation on rare occasions. Exposure to DEET at high doses has also been associated with respiratory and gastrointestinal irritation. Depending on the situation and concentration, DEET provides 2-8 hours of protection. According to the American Academy of Pediatrics (AAP) DEET may be applied to children over the age of two months but should be done so by an adult and in concentrations not exceeding 30%. Care should be taken when applying DEET to clothing or around certain materials including plastics, rayon, spandex, leather, and painted or varnished surfaces. DEET is an effective solvent and may dissolve some of these materials.

Picaridin: Picaridin (Icaridin, Piperidine, Propidine, INCI, or KBR 3023) is another effective repellent of mosquitoes, ticks, fleas, black flies, and biting midges. It can be as effective as DEET, but without the toxicity and allergenic problems commonly associated with DEET. Picaridin is a relatively new product (introduced to the U.S. market in 2005) and allergenic properties may be discovered once use becomes more widespread. Derived from pepper, this repellent has minimal odor and does not harm plastics or fabric. Picaridin offers 4-8 hours of effectiveness, but, because it is relatively odorless, not irritating or greasy, and doesn’t damage synthetic materials, it is often preferred to DEET.

IR3535: IR3535 (ethyl butyl acetyl aminoproprionate) is a moderately effective repellent of mosquitoes, ticks, and biting flies. Some tests indicate that the relatively non-toxic IR3535 can provide 4-6 hours of effectiveness, however, USDA laboratories found this repellent to be 10-100 times less effective than DEET.

Oil of Lemon Eucalyptus: Oil of lemon eucalyptus (p-menthane 3,8-diol or PMD) is one of many plant-based insect repellents and is effective against mosquitoes, black flies, biting midges, ticks, and gnats. Generally, plant-based repellents do not have the same level of effectiveness as synthetics such as DEET and Picaridin, however, oil of lemon eucalyptus has been shown to offer protection similar to concentrations of 20-30% DEET, but for much shorter periods of time. According to the product label, oil of lemon eucalyptus should not be used on children under the age of three and care must be taken to keep it out of the eyes because it can cause significant eye irritation.

Citronella: Citronella is another natural plant-based product with minimal repellence to mosquitoes. Citronella is often used in candles, torches, and in some topical repellents. In general, citronella based products provide much lower protection from mosquitoes than other repellents and are not effective against ticks and other biting pests.

Essential Oils:  In addition to oil of lemon eucalyptus and citronella, commercially available repellents containing active ingredients such as catnip oil, geranium oil, peppermint oil, soybean oil, and a host of other essential oils are purported to have repellent qualities.  While these oils may offer some mosquito repellence, they tend to do so for short periods of time and have not been found to be effective against other biting arthropods, ticks in particular.

2-Undecanone:  2-undecanone (methyl nonyl ketone or IBI-246) is an oily, plant-based repellent that has shown some effectiveness against ticks and mosquitoes. The use of 2-undecanone as an insect repellent is relatively new; it is most commonly used to repel cats, dogs, and even raccoons. Due to the limited use of 2-undecanone as an insect repellent, adverse effects have not been well documented. Studies indicate that the potential exists for some acute toxicity and mild irritation but further testing is needed.

Permethrin: Permethrin is a pyrethroid that works as a contact insecticide as well as a repellent. The chemical is effective against mosquitoes, flies, ticks, fleas, human lice, and chiggers. It has low mammalian toxicity and is poorly absorbed by the skin. Products containing permethrin are for use on clothing or other fabrics (tents, mosquito netting, etc.) not on skin. The use of permethrin treated clothing in combination with a DEET application provides a formidable barrier against biting insects and can nearly eliminate mosquito bites. Permethrin yard foggers can be an effective short term solution for small outdoor settings, however, some concerns have been raised about potential respiratory and gastrointestinal irritation associated with the prolonged inhalation of permethrin.

Metofluthrin: Metofluthrin is another relatively new chemical repellent. Although it is a repellent, metofluthrin is similar to permethrin, in that it is a type of pyrethroid and is not to be used directly on the skin. Metofluthrin is found in impregnated repellent strips that are placed near outdoor gathering spots, as well as in the replaceable cartridges of battery operated personal repellent devices. These devices emit a small cloud of metofluthrin that acts as an effective repellent against mosquitoes. Concerns have been raised about the safety of these products, as users are exposed to prolonged inhalation of metofluthrin, which has been found to be a neurotoxin in some studies.

Applying Repellents

Once you have determined the type of repellent you would like to use, it is important to follow these general considerations when applying repellents:

  • Remember insect repellents are registered pesticides. Read and follow all directions and precautions on the product label. It is the law.
  • Only apply repellent to exposed skin as directed, never under clothing.
  • Do not apply over cuts, wounds, or irritated skin.
  • Do not apply products directly onto your face. Spray your hands and carefully apply to your face, avoiding contact with your eyes and mouth.
  • Do not apply repellents near food or drink items.
  • Do not apply repellents to children under the age of two months. Check label for additional restrictions (lemon of eucalyptus should not be used on children under three)
  • Do not apply to hands or near eyes and mouth of children.
  • Do not allow young children to apply this product.
  • Avoid over-application. Use only what you need.
  • Do not spray when you are in an enclosed area.
  • Do not re-apply unless the label allows additional applications.
  • After returning indoors, wash treated skin with soap and water.
  • Wash treated clothing before wearing it again.
  • The AAP cautions against use of a repellent that is combined with sunscreen. The sunscreen will need to be reapplied more often than the repellent so you might end up using too much repellent.

For more information regarding the safe use of insect repellents please see:

When Using Pesticides


Pest Management Unit
Cooperative Extension Diagnostic and Research Laboratory
17 Godfrey Drive, Orono, ME 04473-1295
1.800.287.0279 (in Maine)

Information in this publication is provided purely for educational purposes. No responsibility is assumed for any problems associated with the use of products or services mentioned. No endorsement of products or companies is intended, nor is criticism of unnamed products or companies implied.

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