Mechanism of action
DEET works primarily by interfering with the olfactory receptors of insects and arthropods, preventing them from detecting human hosts. It does not kill insects but acts as a spatial repellent by creating a vapor barrier on the skin that confuses the chemosensory system of mosquitoes, ticks, and other biting arthropods.
The compound binds to odorant receptors on insect antennae, particularly blocking detection of lactic acid, carbon dioxide, and other human-derived attractants. This sensory confusion causes insects to avoid treated skin surfaces. DEET also has some direct effects on insect neurons, though repellent activity is the primary mechanism.
The duration of protection is concentration-dependent, with higher concentrations providing longer protection rather than greater efficacy. Formulations between 20-50% DEET provide practical protection for several hours, with diminishing returns above 50% concentration.
- DEET toxicity presents with CNS effects: confusion, ataxia, seizures, especially in children with excessive application
- DEET interferes with insect olfactory receptors, blocking detection of human host cues like lactic acid and CO2
- Higher DEET concentrations increase duration of protection (not efficacy): 10% lasts 2h, 30% lasts 6-8h
- DEET reduces sunscreen SPF by up to 30%; apply sunscreen first, then DEET after drying
- Contraindicated in infants under 2 months; use maximum 30% concentration in children
- Classic exam scenario: pediatric seizure after occlusion of freshly applied high-concentration DEET under clothing
- Treatment of DEET toxicity is supportive: benzodiazepines for seizures, skin decontamination, no specific antidote
- Safe in pregnancy for malaria prevention; benefit of vector-borne disease prevention outweighs theoretical risk
Indications
DEET is indicated for topical application to prevent bites from:
- Mosquitoes (including vectors of malaria, dengue, Zika, yellow fever, West Nile virus)
- Ticks (prevention of Lyme disease, Rocky Mountain spotted fever, ehrlichiosis)
- Fleas, chiggers, and biting flies
- Other disease-transmitting arthropods
It is recommended for travelers to endemic areas for mosquito-borne and tick-borne diseases and for outdoor workers and recreational users in areas with significant arthropod exposure. The CDC and WHO recommend DEET as a first-line prevention strategy for vector-borne disease prevention.
DEET is available in various formulations including lotions, sprays, wipes, and combination products with sunscreen, though combination products may reduce the effectiveness of sunscreen due to increased absorption or require more frequent application.
Pharmacokinetics
Absorption: DEET is absorbed through intact skin, with approximately 10-20% of the applied dose entering systemic circulation. Absorption increases with higher concentrations, occlusion, damaged skin, and in children due to higher surface area to body weight ratio.
Distribution: After dermal absorption, DEET distributes into tissues and can cross the blood-brain barrier. The volume of distribution has not been fully characterized in humans.
Metabolism: DEET undergoes hepatic metabolism primarily via oxidation and glucuronidation. The main metabolites include N,N-diethyl-m-toluamide carboxylic acid and other oxidative products. These metabolites are generally less toxic than the parent compound.
Elimination: Metabolites are excreted primarily in urine. The elimination half-life is approximately 2-3 hours for systemically absorbed DEET. Most of the absorbed dose is eliminated within 24 hours.
DEET that remains on the skin surface evaporates over time or is removed by washing, sweating, or mechanical abrasion. Repeated daily application can lead to accumulation in adipose tissue.
Adverse effects
DEET is generally safe when used as directed, but adverse effects can occur, particularly with misuse:
Local effects
- Skin irritation, rash, or contact dermatitis (most common)
- Urticaria or allergic reactions (rare)
- Eye irritation if accidentally applied near eyes
- Damage to synthetic fabrics, plastics, leather, and painted surfaces
Systemic effects (rare, usually with excessive use or ingestion)
- CNS toxicity: Confusion, disorientation, ataxia, tremor, seizures, encephalopathy
- Headache, dizziness, mood changes
- Nausea, vomiting
- Cardiovascular effects including hypotension and bradycardia (rare)
- Respiratory distress in severe poisoning
Special populations
- Children: Higher risk of systemic toxicity due to greater surface area to weight ratio and potential for hand-to-mouth transfer. Seizures have been reported with excessive application or use of high concentrations.
- Pregnancy: Generally considered safe for topical use, but systemic absorption occurs. Risk-benefit should be assessed in malaria-endemic areas.
Severe toxicity is almost exclusively associated with ingestion, prolonged excessive dermal application, or application to large body surface areas in young children. Deaths from DEET toxicity are extremely rare but have been reported.
Contraindications and warnings
Contraindications:
- Known hypersensitivity to DEET or formulation components
- Application to damaged, irritated, or sunburned skin
- Use under occlusive dressings or clothing immediately after application
Warnings and precautions:
- Do not apply to hands of young children (risk of ingestion or eye contact)
- Avoid application near eyes, mouth, and mucous membranes
- Do not apply over cuts, wounds, or irritated skin
- Use the lowest effective concentration for the required duration of protection
- Wash treated skin after returning indoors
- Do not spray in enclosed areas; use adequate ventilation
- Not for internal use; poisoning requires immediate medical attention
Age restrictions: The American Academy of Pediatrics recommends avoiding DEET in infants under 2 months. Concentrations should not exceed 30% in children. Some authorities recommend maximum 10% concentration in children under 12 years.
Pregnancy and lactation: DEET is considered safe for pregnant and breastfeeding women when used as directed, particularly in malaria-endemic regions where the benefit of disease prevention outweighs theoretical risks. It is classified as pregnancy category C by older FDA classifications.
Special precautions: Avoid prolonged or excessive use. When combined with permethrin-treated clothing, lower DEET concentrations may provide adequate protection.
Drug interactions
DEET has limited drug interactions when used topically as directed:
Sunscreen: DEET can reduce the SPF effectiveness of sunscreen by up to 30% and may increase systemic absorption of both products. Apply sunscreen first, allow it to dry, then apply DEET. Consider using higher SPF sunscreen to compensate.
Topical medications: DEET may enhance percutaneous absorption of other topically applied medications or chemicals. Avoid simultaneous application of multiple topical products on the same skin area.
Permethrin: Often used in combination with DEET-treated skin (permethrin on clothing, DEET on exposed skin) with no known adverse interaction. This combination strategy is recommended for high-risk areas.
Alcohol: Systemic DEET absorption may be increased by alcohol consumption, though clinical significance is unclear.
DEET does not significantly interact with oral medications when used topically. In cases of ingestion or severe systemic toxicity, DEET may theoretically interact with CNS depressants or medications affecting seizure threshold, but this is not well-documented.
Avoid applying DEET immediately before or after other topical products to minimize interaction potential and altered absorption kinetics.
Clinical pearls
- Concentration matters for duration, not efficacy: 10% DEET provides approximately 2 hours of protection, 30% provides 6-8 hours. Concentrations above 50% offer minimal additional benefit.
- Classic exam presentation: Child with seizures after excessive insect repellent application, especially with occlusion (clothing immediately after application) or repeated applications.
- Not mosquitocidal: DEET repels but does not kill mosquitoes. It works by masking the attractant signals that draw insects to humans.
- Efficacy factors: Sweating, swimming, and rain reduce protection duration. Reapplication should follow product guidelines and wash off after protection is no longer needed.
- Comparative effectiveness: DEET remains the gold standard against which other repellents are measured. Picaridin is a comparable alternative with similar efficacy and fewer concerns about damaging synthetic materials.
- Vector-borne disease prevention: In endemic areas, DEET use significantly reduces risk of malaria, dengue, Zika, and tick-borne diseases when applied correctly.
- Military use: Developed by the US Army in 1946 and remains standard issue for military personnel in endemic regions, typically in 30-35% formulations.
- Toxicity management: CNS toxicity including seizures is treated supportively with benzodiazepines, airway management, and decontamination (washing skin, activated charcoal if ingested and presenting early). There is no specific antidote.
- Special populations: CDC recommends DEET for pregnant women traveling to malaria-endemic areas. Benefits of disease prevention outweigh minimal theoretical risks from topical use.
- Application strategy: Apply to exposed skin only, use just enough to cover, avoid overapplication, and always wash hands after application to prevent inadvertent ingestion or eye contact.
Practice questions
1. A 4-year-old boy is brought to the emergency department with altered mental status and generalized tonic-clonic seizures that began 2 hours ago. His mother reports applying insect repellent liberally before dressing him in long sleeves and pants for an outdoor camping trip earlier today. On examination, he is postictal with temperature 37.2°C, pulse 110/min, respirations 22/min, and blood pressure 95/60 mmHg. Neurological examination shows confusion and mild ataxia. What is the most likely cause of his presentation?
2. A 28-year-old pregnant woman at 20 weeks gestation is planning travel to a malaria-endemic region in West Africa. She is concerned about using insect repellent during pregnancy. Which of the following is the most appropriate advice regarding DEET use?
3. A 35-year-old man applies a 30% DEET lotion and SPF 30 sunscreen simultaneously before hiking. After 3 hours of sun exposure, he develops more extensive sunburn than expected. Which of the following best explains this observation?
Frequently asked questions
How does DEET work as an insect repellent?
DEET interferes with olfactory receptors on insect antennae, blocking their ability to detect human-derived chemical attractants such as lactic acid, carbon dioxide, and body odor. This creates a sensory confusion that causes mosquitoes, ticks, and other arthropods to avoid treated skin surfaces. DEET does not kill insects but acts as a spatial repellent through this olfactory disruption mechanism.
What are the side effects of DEET?
Most side effects are mild and include skin irritation, rash, or contact dermatitis at application sites. Serious toxicity is rare but can occur with excessive use, especially in children, and includes CNS effects such as confusion, ataxia, tremor, and seizures. Eye irritation can occur if accidentally applied near eyes. Systemic toxicity typically requires misuse such as ingestion, prolonged occlusive application, or use of very high concentrations over large body surface areas.
Is DEET safe for children and pregnant women?
DEET should not be used in infants under 2 months of age. For older children, concentrations should not exceed 30%, and some guidelines recommend maximum 10% for children under 12 years. DEET is considered safe in pregnancy and breastfeeding when used as directed, particularly in malaria-endemic areas where preventing mosquito-borne disease outweighs theoretical risks. The CDC specifically recommends DEET for pregnant travelers to endemic regions.
What is the difference between 10% and 30% DEET concentration?
The difference lies in duration of protection, not effectiveness at repelling insects. A 10% DEET formulation provides approximately 2 hours of protection, while 30% provides 6-8 hours. Higher concentrations do not repel insects better; they simply last longer before requiring reapplication. Concentrations above 50% provide minimal additional duration benefit and increase risk of systemic absorption and adverse effects.
Can DEET be used with sunscreen?
Yes, but DEET can reduce sunscreen effectiveness by up to 30% and may increase absorption of both products. The recommended approach is to apply sunscreen first, allow it to dry completely, then apply DEET. Consider using a higher SPF sunscreen to compensate for the reduced effectiveness. Combination sunscreen-DEET products are available but may require more frequent reapplication to maintain adequate sun protection.
Conditions it is used for
Related drugs
Sources and further reading
DailyMed (FDA labels)StatPearls (NCBI Bookshelf)MedlinePlusWHO ATC/DDD index: P03BX01
Educational content for medical students, prepared by the WhiteCoat Pro editorial team with AI assistance; every page is reviewed by a second AI model for factual errors. It is not medical advice and does not replace the product label, local guidelines or a clinician.