The Medical Letter on Drugs and Therapeutics
Insect Repellents
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Summary: Insect Repellents
  • DEET is highly effective against mosquito and tick bites and is generally safe.
  • Picaridin appears to be as effective against mosquitoes as equivalent concentrations of DEET and may be better tolerated on the skin. It also repels ticks.
  • IR3535 at concentrations ≥10% and oil of lemon eucalyptus (OLE) can also be effective in repelling mosquitoes and ticks.
  • Published data on the efficacy of 2-undecanone are limited.
  • Citronella oil-based insect repellents provide short-term protection against mosquitoes, but not ticks. Other essential oils provide limited and variable protection against mosquitoes.
  • Wearing clothing treated with the insecticide permethrin in addition to using DEET or picaridin on exposed skin may provide the best protection against mosquitoes and ticks.
  • Wearable devices such as wristbands are not effective.

Use of insect repellents is strongly recommended by the Centers for Disease Control and Prevention (CDC) and the Environmental Protection Agency (EPA) to prevent infections transmitted by mosquitoes and ticks. Insect repellents applied to exposed skin should be used in conjunction with other preventive measures such as wearing pants and long-sleeved shirts, and avoiding outdoor activities during peak mosquito-biting times.1 Mosquitoes can transmit Zika, chikungunya, dengue, West Nile, eastern equine encephalitis, and yellow fever viruses, as well as malaria. Ticks can transmit Lyme disease, rickettsial diseases such as Rocky Mountain spotted fever, and viruses such as Powassan virus.

DEET — The topical insect repellent N,N-diethyl-m-toluamide (DEET) is highly effective against mosquito and tick bites.2 It also repels chiggers, fleas, gnats, and some flies. DEET is available in concentrations of 5-99%; higher concentrations typically provide longer-lasting protection,3 but increasing the concentration above 50% has not been shown to improve efficacy.

Long-acting polymer-based or liposomal DEET formulations containing concentrations of 30-34% have been shown to protect against mosquitoes for up to 12 hours. The CDC recommends using concentrations ≥20% in adults for protection against both mosquitoes and ticks.

Reviews of the safety and toxicity of topically applied DEET indicate that it is generally safe.2,4 Toxic and allergic reactions to DEET have been uncommon, and serious adverse effects are rare.4 Rashes ranging from mild irritation to urticaria and bullous eruptions have been reported. Patients find that some DEET formulations feel uncomfortably oily or sticky on their skin. DEET can damage clothing made from synthetic fibers and plastics on eyeglass frames and watches.

Children – The American Academy of Pediatrics recommends using DEET formulations containing concentrations of 10-30% on children and infants >2 months old. Neurologic adverse events have occurred in infants and children, usually with prolonged or excessive use that sometimes included ingestion of the product.

PICARIDIN — Picaridin provides protection against mosquitoes, ticks, flies, fleas, and chiggers. It is available in concentrations of 5-20%; higher concentrations typically provide longer lasting protection.5 Picaridin appears to be at least as effective against mosquitoes as DEET at similar concentrations.6

Picaridin can cause skin and eye irritation, but it appears to be better tolerated on the skin than DEET. It is odorless, non-greasy, and does not damage fabric or plastic, but it can discolor leather and vinyl. In a review of data from US poison centers, ingestion of picaridin-based insect repellents resulted in only minor toxicity (mild oral or skin irritation, mild GI symptoms) that did not require referral to a healthcare facility.7

Children – The American Academy of Pediatrics recommends formulations of picaridin containing concentrations of 5-10% for use on children as an alternative to DEET.

IR3535 — IR3535 (3-[N-Butyl-N-acetyl]-aminopropionic acid, ethyl ester), a synthetic version of β-alanine, repels mosquitoes, deer ticks, and flies. It is available in concentrations of 7.5% and 20% in the US (see Table 1). Concentrations ≥10% have been found to be effective against mosquito bites for several hours.8 Two studies found the 7.5% concentration to be ineffective.3,9 IR3535 can cause eye irritation, and it may damage clothing and plastics.

Children – According to the EPA, IR3535 is safe for use on children >2 months old.

OIL OF LEMON EUCALYPTUS — Oil of lemon eucalyptus (OLE; p-menthane-3,8-diol [PMD]), which repels mosquitoes, ticks, flies, gnats, and biting midges, occurs naturally in the lemon eucalyptus plant.2 It is chemically synthesized for commercial use as a repellent. In field studies against malaria-transmitting mosquitoes, OLE provided up to 6 hours of protection against mosquito bites.8 It has demonstrated efficacy equivalent to that of DEET against mosquitoes in some laboratory and field studies.10 OLE can cause eye and skin irritation, including allergic skin reactions.11

Children – OLE products are not recommended for use on children <3 years old.

2-UNDECANONE — A relatively new insect repellent, 2-undecanone is derived from the wild tomato plant.12 A synthetic version is commercially available in a 7.75% spray formulation (BioUD). Published data on the efficacy of 2-undecanone are limited.2 According to the product label, BioUD is effective for up to 4.5 hours against mosquitoes and up to 2 hours against ticks. It can have a strong odor.

CITRONELLA — Citronella oil-based insect repellents provide short-term protection against mosquitoes, but they are probably not effective against ticks. In laboratory studies, various concentrations of citronella oil were less effective than DEET against mosquito bites in duration of protection.13 The protection times for most citronella oil products are 2 hours or less, and they can cause skin irritation.

OTHER ESSENTIAL OILS — Essential oils obtained from raw botanical material, including clove, geraniol, catnip, and patchouli, provide limited and variable protection against mosquitoes. High concentrations can be irritating to the skin.14,15

SUNSCREENS AND INSECT REPELLENTS — Topical insect repellents can be used with sunscreens; the repellent should be applied after the sunscreen. Applying DEET after sunscreen has been shown to reduce the sun protection factor (SPF) of the sunscreen, but applying sunscreen after DEET may increase absorption of DEET. The CDC does not recommend use of products that combine a sunscreen with an insect repellent because the sunscreen may need to be reapplied more often and in greater amounts than the repellent.

PERMETHRIN — A synthetic pyrethroid contact insecticide, permethrin can be sprayed on clothing, mosquito nets, tents, and sleeping bags to repel and kill mosquitoes and ticks. Permethrin-impregnated clothing is available commercially; it remains active for several weeks through multiple launderings with minimal transfer to the skin.16 An indoor laboratory study found that subjects wearing permethrin-treated sneakers and socks were 73.6 times less likely to be bitten by a tick than those wearing untreated footwear.17 Studies in outdoor workers in North Carolina wearing uniforms treated with a long-lasting formulation of permethrin using a commercially available factory-based method found that the clothing protected against mosquito and tick bites for at least 1 year.18,19 No significant adverse effects have been reported from wearing permethrin-treated clothing.11

WEARABLE DEVICES — Several insect repellents, including DEET, OLE, and citronella, are commercially available in wearable devices such as wristbands. These devices are not effective.20,21

PREGNANCY — The CDC considers EPA-registered formulations of DEET, picaridin, IR3535, OLE, and 2-undecanone safe for use during pregnancy.22 According to the EPA, there is no evidence that exposure to permethrin results in adverse effects in pregnant or nursing women or developmental adverse effects in their children.23 In its Zika virus prevention guidelines, the American College of Obstetricians and Gynecologists recommended that pregnant women traveling to areas where Zika has been reported use an EPA-registered DEET product and permethrin-treated clothing, cover exposed skin, and stay in air-conditioned or indoor areas.24,25


  1. CDC/EPA. Joint statement on insect repellents from the Environmental Protection Agency and the Centers for Disease Control and Prevention. July 17, 2014. Available at: Accessed August 15, 2019.
  2. QD Nguyen et al. Insect repellents: an updated review for the clinician. J Am Acad Dermatol 2018 Nov 2 (epub).
  3. MS Fradin and JF Day. Comparative efficacy of insect repellents against mosquito bites. N Engl J Med 2002; 347:13.
  4. Chen-Hussey et al. Assessment of methods used to determine the safety of the topical insect repellent N,N-diethyl-m-toluamide (DEET). Parasit Vectors 2014; 7:173.
  5. Picaridin – a new insect repellent. Med Lett Drugs Ther 2005; 47:46.
  6. L Goodyer and S Schofield. Mosquito repellents for the traveller: does picaridin provide longer protection than DEET? J Travel Med 2018; 25(suppl_1):S10.
  7. NP Charlton et al. The toxicity of picaridin containing insect repellent reported to the National Poison Data System. Clin Toxicol (Phila) 2016; 54:655.
  8. LI Goodyer et al. Expert review of the evidence base for arthropod bite avoidance. J Travel Med 2010; 17:182.
  9. SP Frances et al. Comparative field evaluation of repellent formulations containing DEET and IR3535 against mosquitoes in Queensland, Australia. J Am Mosq Control Assoc 2009; 25:511.
  10. SP Carroll and J Loye. PMD, a registered botanical mosquito repellent with DEET-like efficacy. J Am Mosq Control Assoc 2006; 22:507.
  11. JH Diaz. Chemical and plant-based insect repellents: efficacy, safety, and toxicity. Wilderness Environ Med 2016; 27:153.
  12. BE Witting-Bissinger et al. Novel arthropod repellent, BioUD, is an efficacious alternative to DEET. J Med Entomol 2008; 45:891.
  13. C Kongkaew et al. Effectiveness of citronella preparations in preventing mosquito bites: systematic review of controlled laboratory experimental studies. Trop Med Int Health 2011; 16:802.
  14. Y Trongtokit et al. Comparative repellency of 38 essential oils against mosquito bites. Phytother Res 2005; 19:303.
  15. MY Lee. Essential oils as repellents against arthropods. Biomed Res Int. 2018 Oct 2 (epub).
  16. KM Sullivan et al. Bioabsorption and effectiveness of long-lasting permethrin-treated uniforms over three months among North Carolina outdoor workers. Parasit Vector 2019; 12:52.
  17. NJ Miller et al. Tick bite protection with permethrin-treated summer-weight clothing. J Med Entomol 2011; 48:327.
  18. MF Vaughn et al. Long-lasting permethrin impregnateduniforms: a randomized-controlled trial for tick bite prevention. Am J Prev Med 2014; 46:473.
  19. B Londono-Renteria et al. Long-lasting permethrin-impregnated clothing protects against mosquito bites in outdoor workers. Am J Trop Med Hyg 2015; 93:869.
  20. SD Rodriguez et al. Efficacy of some wearable devices compared with spray-on insect repellents for the yellow fever mosquito, Aedes aegypti (L.) (Diptera: Culcidae). J Insect Sci 2017; 17:24.
  21. RV Patel et al. EPA-registered repellents for mosquitoes transmitting emerging viral disease. Pharmacotherapy 2016; 36:1272.
  22. CDC. Zika virus. Prevent mosquito bites. Available at www.cdc. gov/zika/prevention/prevent-mosquito-bites.html. Accessed August 15, 2019.
  23. US Environmental Protection Agency. Repellent-treated clothing. Last updated March 29, 2016. Available at: Accessed August 15, 2019.
  24. American College of Obstetricians and Gynecologists. Practice advisory interim guidance for care of obstetric patients during a Zika virus outbreak. Available at Accessed August 15, 2019.
  25. BJ Wylie et al. Insect repellants during pregnancy in the era of the Zika virus. Obstet Gynecol 2016; 128:1111.
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