DEET for Tick Repellent Efficacy, Concentration, and Safety

The question most readers bring to DEET is a short one: does it work against ticks, what concentration should I use, and is it safe? The answers involve a distinction that the marketing rarely makes — much of the classic DEET evidence base was built on mosquitoes, and ticks respond differently to the chemistry. What follows is what public-health authorities and the peer-reviewed literature actually say.

What DEET is

The 2007 Connecticut Agricultural Experiment Station tick management handbook introduces DEET this way:

"The primary active ingredient in most insect/tick repellents today is DEET (N,N-diethyl-3- methylbenzamide, also known as N,N-diethyl-m-toluamide). DEET is the most effective, broad-spectrum repellent ever discovered, effective against mosquitoes, biting flies, chiggers, fleas and ticks." — CAES, 2007, pp. 44–45. Tick Management Handbook:...

A 2025 review in Veterinary Sciences places DEET in the broader repellent landscape, with specific efficacy and safety details threaded into the sections that follow.

One handbook "estimates that over one-third of the U.S. population will use a DEET-based product" (CAES 2007), and DEET-containing products "range in concentration from 4% to 100% DEET and are available as an aerosol can, pump spray bottle, stick, lotion, cream, or towelette for application to skin or clothing" (CAES 2014).

Efficacy against ticks

DEET repels ticks, but not as cleanly as it repels mosquitoes. CDC's 2016 tickborne rickettsial disease guidelines put the operative range this way:

"N,N-diethyl-m-toluamide (DEET) effectively repels ticks and can be applied directly to the skin. Products with 20%–30% DEET are considered optimal for protection against most tick species, and concentrations >50% do not confer additional protection." — CDC, 2016, pp. 33–34. Diagnosis and Management...

The same pattern — 20–30% as the useful window, >50% contributing little — appears in the 2020 Clinical Practice Guidelines from IDSA, AAN, and ACR, which note that "products containing >50% DEET do not offer a meaningful increase in protection time over lower concentrations" (IDSA 2020).

How well does 20–30% actually work against a tick crawling on you? The numbers depend heavily on whether DEET is applied to skin or to clothing. For the blacklegged tick (Ixodes scapularis), the vector of Lyme disease, one handbook summarizes the literature this way: "When applied to clothes, 30% and 20% DEET were found to be 92% and 86% effective against I. scapularis, respectively, but skin applications were reported to be only 75 to 87% effective against crawling ticks in a second study" (CAES 2007). An important caveat sits inside that number: "Concentrations of DEET that might prevent tick attachment may not deter a tick from walking across the skin to unexposed and untreated areas" (CAES 2014).

A 2025 review of chemical tick control puts the broader efficacy picture this way: "Studies indicate that DEET provides significant protection, with formulations containing 20% DEET offering up to 12 h of protection against tick bites" (MDPI 2025), though "the efficacy of DEET can vary based on concentration and environmental conditions" (MDPI 2025).

Concentration and duration

"Higher concentrations generally provide longer protection, but increasing the concentration does not proportionally increase protection time" (CAES 2007). The often-quoted numbers for the diminishing-returns curve come from a mosquito study: "a 23.8% DEET formulation provided an average of 5 hours of complete protection, while 6.65% DEET provided slightly under 2 hours of protection" (CAES 2007).

Protection also fades in ways that don't depend on the chemistry alone. "The effectiveness of DEET on the skin is influenced by the concentration of DEET, absorption through the skin, evaporation, sweating, air temperature, wind, and abrasion of the treated surface by rubbing or washing" (CAES 2014). Practically, "DEET is only effective for one to several hours and must be reapplied periodically" (CAES 2014). On longer-wearing formulations: "Several controlled-release, extended duration products with DEET have been developed which decrease skin absorption and increase protection time" (CAES 2014).

Compared with the alternatives

The 2020 IDSA/AAN/ACR guidelines place DEET alongside several other registered active ingredients. See also Picaridin Tick Repellent.

"For the prevention of tick bites, we recommend N,N-Diethyl-meta-toluamide (DEET), picaridin, ethyl-3-(N-n-butyl-N-acetyl) aminopropionate (IR3535), oil of lemon eucalyptus (OLE), p-methane-3,8-diol (PMD), 2-undecanone, or permethrin (strong recommendation, moderate-quality evidence)." — IDSA, 2020. Clinical Practice Guideli...

The guidelines' review of the evidence concludes that "the use of DEET, picaridin, IR3535, oil of lemon eucalyptus (OLE), p-methane-3,8-diol (PMD, the synthetic active ingredient in oil of lemon eucalyptus), 2-undecanone, and permethrin reduced the number of ticks detected crawling on or attached to subjects compared with controls" (IDSA 2020). Further reading: Ir3535 Oil Lemon Eucalyptus Tick Repellent. Beyond that set, "Other commercially available products, including botanical agents and essential oils (eg, essential oils of rosemary, cinnamon leaf, lemongrass, geraniol, nootkatone, and carvacrol ) cannot be recommended due to insufficient evidence" (IDSA 2020). Related: Tick Repellent Myths Ineffective.

For clothing, DEET is not the first choice. The same guidelines find that clothing treated with permethrin is "more effective compared with clothes treated with DEET" (IDSA 2020). A further note on materials: DEET "will harm some synthetic fabrics (rayon and spandex), plastics (watch crystals and eyeglass frames), and car and furniture finishes" (CAES 2014).

Safety profile

DEET's safety record is the most studied part of its story. The 2007 CAES handbook summarizes it directly:

"Safe Use of DEET DEET has been used by millions of Americans for at least 40 years and has a remarkable safety record. The incidence of adverse reactions is extremely low with fewer than 50 cases of serious effects documented in the medical literature since 1960. The Environmental Protection Agency (EPA) conducted a review of DEET and believes that normal use of DEET does not present a health concern to the general population when used according to label directions (Reregistration Decision document available from the EPA)." — CAES, 2007, pp. 46–47. Tick Management Handbook:...

The 2020 IDSA/AAN/ACR guidelines reach a similar conclusion: "decades of use show there is a very low risk of adverse effects when used as labeled" (IDSA 2020), and "Despite hundreds of millions of annual applications of DEET, reports of encephalopathy are rare and may not differ from the background rate in the general population" (IDSA 2020). Adverse events, when they occur, tend to cluster around misuse: "Reported cases often involved ingestion of DEET, applications of high concentrations of DEET and over application of product contrary to label directions" (CAES 2014).

That does not mean zero reactions. "some allergic, toxic, and neurological reactions to DEET have been reported in medical literature" (CAES 2014). A 2025 review flags the same caveat for high concentrations: "Reports have indicated potential neurotoxic effects at high concentrations, raising questions about its safety, particularly for vulnerable populations such as children" (MDPI 2025).

Children and infants

The pediatric guidance is where authorities diverge, and the divergence matters. In shorthand: "The American Academy of Pediatrics recommends not more than 30% DEET be used on children and none on infants younger than 2 months of age" (CAES 2014). The 2007 CAES handbook offered the same ceiling — "A concentration of DEET up to 30% for adults and children over 2 years of age is the maximum concentration currently recommended by the American Academy of Pediatrics (AAP)" (CAES 2007) — with the additional note to "Apply sparingly to small children" (CAES 2007).

Applying it

"Apply DEET sparingly to exposed skin, and spray on clothing when possible" (CAES 2014). On reapplication, the 2020 guidelines note that "repellents may need to be reapplied after swimming, washing, or heavy perspiration" (IDSA 2020). On combination sunscreen-plus-DEET products, the same guidelines discourage them: "frequent application of the sunscreen may exceed the recommended exposure to the repellent" (IDSA 2020), and "sunscreen may increase the absorption of DEET through the skin" (IDSA 2020). "the FDA recommends that sunscreen be applied before DEET" (IDSA 2020).