In the age of Zika, knowing which insect repellents are safe and effective, is more important than ever. Luckily, The Medical Letter, a reliable source of unbiased information about pharmaceuticals, recently reviewed insect repellents. Here is what they found.
Repellents containing DEET (N,N-diethyl-m-toluamide for those of you who care) have the best documentation of effectiveness against mosquitoes. It comes in concentrations of between 5-100%. Although higher concentrations last longer, there is no added benefit to going above 50%. Although DEET can damage clothes made from synthetic fiber and plastics on eyeglasses, it is generally considered safe with the main side effects being skin reactions, such as hives and fluid-filled blisters. According to the Medical Letter review,
“toxic and allergic reactions to DEET have been uncommon and serious adverse events are rare.”
The CDC has deemed DEET safe for children and infants >2-months old, although the American Academy of Pediatrics recommends using concentrations in the range of 10 to 30%. Serious sided effects in kids, such as toxic encephalopathy (a brain disorder) has been reported with prolonged or excessive use that sometimes included drinking it. Relevant to the current concern over Zika, the CDC also considers DEET-containing formulations that are registered with the EPA to be safe for use during pregnancy.
Examples of DEET-containing repellents include Cutter Skinsations 7% pump spray (protection lasts 1-3 hours), Repel Scented Family 15% aerosol spray (lasts 5-8 hours), and Off Deep Woods VIII 25% aerosol spray (lasts 8 hours). Sawyer Ultra 30 Liposome Controlled Release (30%) and Ultrathon (34%) last 11 and 12 hours, respectively.
Picaridin seems to be better tolerated on the skin than DEET, although it can cause skin and eye irritation. Unlike DEET, it does not feel sticky or oily and it does not damage fabrics or plastic. Although there aren’t as many studies on picaridin as there are on DEET, it is noteworthy that in one controlled trial, picaridin at a concentration of 19.2% prevented mosquito bites as effectively as a long-acting 33% DEET formulation. The American Academy of Pediatrics has said formulations of picaridin in concentrations of 5-10% can be used on children as an alternative to DEET. Products with Picaridin include Cutter Advanced wipes (5.75%), Avon Skin So Soft Bug Guard Plus Picaridin spray (10%), and Natrapel spray (20%). All three provide protection for up to 8 hours.
IR3535 in concentrations >10% has been found to be effective against mosquito bites for several hours. Coleman Skin Smart is a spray with a 20% concentration. It lasts 8 hours. Avon Skin So Soft Bug Guard Plus IR3535 comes as a 7.5% lotion said to last 2 hours. According to the Medical Letter, two studies have found a concentration of 7.5% ineffective.
Oil of Lemon Eucalyptus
Oil of Lemon Eucalyptus (OLE or p-menthane-3,8 diol [PMD]) appears naturally in the lemon eucalyptus plant. It has also been produced by chemical synthesis for commercial use. Studies have shown that it can provide protection against mosquito bites for up to 6 hours. It is not recommended to use OLE products on children. OLE-containing products include Coleman Botanicals and Repel Lemon Eucalyptus. Both come as 30% sprays that last 6 hours and 7-8 hours, respectively.
In laboratory studies, various concentrations of citronella were much less effective against mosquito bites than DEET, and the protection times only lasted from 1.5 to 5 hours.
A variety of essential oils, including clove, geraniol, and patchouli, have been tested and found to provide “limited and variable protection against mosquitoes.” High concentrations may be more effective, but can irritate the skin.
Using sunscreen with insect repellents
Although these two products can be used together, the Medical Letter recommends applying the repellent after the sunscreen. The SPF of sunscreen may be reduced if DEET-containing products are applied second, but applying sunscreen after DEET products may lead to increased absorption of DEET. The CDC warns against using products that contain both a sunscreen and an insect repellent because “the sunscreen may need to be applied more often and in greater amounts than the repellent.”
Permethrin clothing and gear
Permethrin, a contact insecticide, is used on clothes, tents, sleeping bags, and mosquito nets to repel and kill mosquitoes. When a permethrin product is sprayed on clothing, it has been shown to remain active for several weeks and through multiple launderings. There is minimal transfer to the skin. You can also buy clothing impregnated with permethrin. Studies in outdoor workers have found that the clothing provided protection against mosquito bites for at least a year. Permethrin 0.5% sprays include Sawyer Premium Permethrin Clothing and Repel Permethrin Clothing and Gear. Permethrin-impregnated clothing is available in most camping and outdoor stores as well as online.
The best protection?
The Medical Letter concludes that wearing protective clothing (e.g., long-sleeve, high-necked shirts) treated with Permethrin in addition to using an effective mosquito repellent, such as DEET or picaridin, may provide the best protection of all. So, there you go. If you are going to be in an area with mosquitoes, apply an effective repellent and then cover-up. The best mosquito bite is no bite at all.