Apply insect repellent to exposed skin following label instructions. They reflect the conditions under which each product has been tested and often identify which insects the product targets.
Which repellent to use? For longest protection, synthesized active ingredients such as DEET and picaridin can last 4 to 10+ hours; see product labels for time estimates. If you prefer to keep it natural, you’ll need to reapply often. Repellents using essential plant oils are believed to be effective for 30 minutes to 2+ hours.
Apply permethrin to clothing, or wear clothing pretreated with the compound such as Insect Shield® apparel. Permethrin kills ticks that linger on treated fabric, and it deters mosquitoes from biting through clothing. Tip: Applying insect repellent under clothing is ineffective; don’t waste your time.
Around a campsite or backyard patio, use insect-repelling candles, diffusers, mosquito coils and mosquito sticks. These devices are most effective in windless conditions.
For serious swarms, wear a headnet. Add netted coverings (bug jacket, bug pants) as needed.
Note: Insect repellents are not effective against stinging insects (bees, wasps, hornets).
Background: Developed by U.S. Army in 1946. Used by millions since 1957. World’s most widely used repellent. Chemical name: N,N-diethyl-m-toluamide or N,N-diethly-3-methyl-benzamide.
Types: Concentrations range from 10% (for about 2 hours of protection) to 98% (up to 10 hours). Controlled-release “micro-encapsulated” formulas of 30%-34% DEET can potentially protect for 11-12 hours. DEET is encapsulated in a polymer, which permits its gradual release.
Safety: Extensively tested for safety; registered with EPA; endorsed for use by the CDC.
EPA: “Based on the available toxicology data, the Agency believes that the normal use of DEET does not present a health concern to the general U.S. population.” Rare anecdotal reports have connected DEET with seizures, but no lab data has confirmed such a link.
Considered a “plasticizer”—DEET can damage rubber, plastic, leather, vinyl, rayon, spandex, elastic, auto paint. After applying DEET, wash hands before handling these materials. Be careful, for example, with plastic eyeglass frames and golf club grips. DEET will not damage cotton, wool, nylon.
DEET in a controlled-release, polymer-encapsulated formula is far less likely to act as a plasticizer. A Sawyer rep tells REI that only 2% to 3% of the DEET is outside the encapsulations at any one time.
For kids, use concentrations of no higher than 30%. Do not use on infants under 2 months.
Presents no known health consequences for pregnant or lactating women.
Do not apply on cuts, wounds or irritated skin.
Note on effectiveness: Combined with permethrin-treated clothing, DEET is considered to be a very good defense against ticks.
Background: DEET alternative developed primarily in Europe beginning in 1998; available in U.S. since 2005. Chemical name: 2-(2-hydroxyethyl)-1-piperidinecarboxylic acid 1-methylpropyl ester. Also known as KBR 3023.
Types: Max concentration currently available: 20%. Protects for up to 8 hours. Refer to product label. In the future, higher concentrations may be available following more toxicology testing.
Safety: Does not damage fabrics, surfaces or materials. For kids, the American Academy of Pediatrics has made no recommendation on the use of picaridin. All repellents should be kept off infants under 2 months.
Note on effectiveness: Considered more effective against flies than DEET.
Synthesized Plant Oils
Synthesized plant oils are technically chemicals. Sometimes marketed as “plant-based” or “botanicals.”
Oil of Lemon Eucalyptus
Background: Registered by EPA in 2000. Chemical name:para-Menthane-3,8-diol (PMD for short). While technically plant-based, this is a chemically synthesizedversion of oil of lemon eucalyptus, not a so-called essential oil.“Pure” oil of lemon eucalyptus is not registered with EPA as an insect repellent.
Type: In a concentration of 30%, it's potentially effective up to 6 hours. Refer to product label.
Safety: May cause a reaction on sensitive skin. Do not use on children under 3 years old due to possible skin irritation.
Background: Developed in Germany by Merck in early 1980s; registered in U.S. in 1999. Chemical name: 3-[N-Butyl-N-acetyl]-aminopropionic acid, ethyl ester. Derived from the amino acid alanine.
Effectiveness: Potential duration of effectiveness:Up to 8 hours. Refer to product label.
Safety: From the EPA: “IR3535 has been used as an insect repellent in Europe for 20 years with no substantial adverse effects. Toxicity tests show that IR3535 is not harmful when ingested, inhaled, or used on skin.” The American Academy of Pediatrics has made no recommendation on the use of IR3535.
Background: First registered with the EPA in 1979 for agricultural use. First registered for use as a repellent on clothing in 1990 by the military. Permethrin was reregistered in 2006 and updated in 2009. It is a synthetic pyrethroid, which acts like a natural extract from chrysanthemums.
Usage: For use on clothing only. Does not harm or irritate skin, but offers no benefits if applied to skin.
Safety: Recommended by the EPA and CDC, permethrin is widely used in agriculture and for household pest control. It does not damage rubber, plastic or fabrics. Considered to be biodegradable; believed to not accumulate in the environment. Spray-on products won't cause stains.
Notes on effectiveness:
Can kill ticks that linger on treated fabric.
Spray-on applications can last 5-6 washings; pretreated clothing may last up to 70 washings.
Can break down in 42 days due to sunlight, even oxygen, according to permethrin-maker Sawyer. The company’s advice: Store treated items in dark, airtight bags such as plastic garbage bags.
Odorless after it has dried.
Does not interfere with the function of moisture-wicking fabrics.
Some permethrin products can be directly applied to dogs and are often used on pet beds. While wet, permethrin can cause fatal poisoning in cats so take caution when applying. However, once dry (on fabric or a dog), it is safe for cats.
The American Academy of Pediatrics advises using no repellent on infants younger than 2 months.
If using DEET, choose concentrations of no greater than 30%.
Any repellent may cause skin irritation for children with sensitive skin. If this occurs, try a different formula.
Kids find sprays more fun to apply, but lotions are typically milder on their skin.
Registered vs. Unregistered Repellents
Active ingredients are what make insect repellents effective. Repellents are considered pesticides, and before most can be marketed they must be registered with the EPA.
However, 30+ active ingredients made from plant oils are exempted from EPA registration. That means they are safe for humans but not necessarily effective.
Registered: Registration means a repellent-maker has provided the EPA with independent test data that indicates a product’s active ingredients, when applied according to label instructions, have been reviewed and approved for human safety and effectiveness. Registered products can display an EPA registration number (usually found on the back label). The Centers for Disease Control (CDC) endorses the use of registered repellents to guard humans from disease-spreading insects.
Examples: DEET, picaridin, oil of lemon eucalyptus, IR3535.
Unregistered: The EPA has a list of 31 “minimum-risk pesticides”—plant-based ingredients (both active and inert) that the agency describes as “demonstrably safe for the intended use.” Data demonstrating effectiveness, though, is not required for these ingredients. Thus repellents in this group could bill themselves as “EPA approved; all-natural.” Yet their duration of effectiveness is uncertain—believed to be between 30 minutes and 2+ hours—well short of what synthetics deliver.
Examples: Essential plant oils (lemongrass oil, cedar oil, geranium oil and many others) or food ingredients (corn oil, cloves and clove oil).
What diseases are transmitted by insects, and which insects do the transmitting? Here are links to information provided by the CDC and FDA.
Malaria. To protect international travelers from aggressive mosquitoes that carry this disease, the CDC advises the use of repellent, treated clothing and bed-netting and preventative pre-travel medication.
Zika virus. Like with malaria, the CDC recommends using repellent, treated clothing and bed-netting to prevent mosquito bites when traveling in areas where Zika virus is found.
Other mosquito-transmitted diseases include yellow fever (a vaccine is available and may be required for entry into some countries), dengue fever, Japanese encephalitis and chikungunya fever. For current news of specific locations, visit the CDC’s travel site.