Chapter 21: Get Total Protection from Mosquitoes and Other Pests
Nothing can ruin your hike or any outdoor adventure like mosquitoes. They can be the difference between a great time and misery. Since you can’t swat them all, you need to know how to keep them away.
Fortunately, there’s a solution that can be nearly 100% effective. The mosquitoes will still be there, but they won’t bite if you use a combination of a DEET-based repellent on exposed skin and a permethrin treatment on your clothing.
That’s the short story. But it’s also helpful to know the stimuli that attract mosquitoes. You should know how to use each product correctly. And you probably want to know the effects of placing these products on your skin and in the environment.
Only female mosquitoes bite. They require a blood meal to produce eggs. They feed every 3 to 4 days and consume more than their own body weight in blood. Different species feed at different times of the day. There are over 175 species of mosquitoes in the United States. Some prefer animals. Some prefer human blood. Mosquitoes require an environment of standing water to develop.
The lifespan of mosquitoes varies from species to species. Males usually live for only about 2 weeks. Females can survive for 6 weeks to about 5 months, depending on the species, conditions, and time of year.
When a mosquito bites, she injects a small amount of saliva to make penetration easier and prevent the blood from quickly clotting. The welt or bump that appears after the bite is a mild allergic reaction to the saliva. When your body senses the intrusion of the mosquito saliva, it releases its own chemicals, or histamines, to fight off the attack. These histamines cause the bite to itch. Of course, some people are more allergic than others. You may also be more allergic to some species than others. You should avoid scratching these welts to prevent bacteria that may by under your fingernails from causing an infection.
Mosquitoes use visual, thermal, and olfactory stimuli to locate you. Olfactory signals, or sense of smell, are probably the most important. Mosquitoes can smell their prey from over 40 yards away. Larger people give off more carbon dioxide, which is probably why mosquitoes prefer adults over children. Mosquitoes prefer men over women, probably for the same reason.
Day feeders may notice your movement or dark clothing if you’re close. Mosquitoes follow your scent and can see you at about 10 yards. They don’t see well, and at 10 yards they have trouble distinguishing you from other objects of similar size and shape. Wear light, muted colors. Wear long sleeves and pants when possible, and clothing with tight weaves.
Our bodies release hundreds of compounds, but carbon dioxide, lactic acid, and uric acid are the best-studied mosquito attractors. Mosquitoes can detect lactic acid with the chemoreceptors on their antennae. These are the receptors that may be confused by DEET-based and picaridin repellents.
When mosquitoes get really close, your skin temperature and sweat are attractive to mosquitoes. Mosquitoes are attracted to heat so larger people are more of a target because of the additional heat as well as carbon dioxide and other compounds. Dark clothing holds more heat, so mosquitoes may be attracted to dark clothing because of the increased heat as well as the visual appeal. There seem to be other attractants in some people’s sweat that attract mosquitoes. Researchers are busy trying to isolate the chemicals in the sweat of people who don’t attract mosquitoes in order to make repellents.
Mosquitoes are sometimes attracted to fragrances, especially floral ones, so watch what soaps, lotions, deodorants, and hair care products you use. Use products that are unscented and leave all perfumes home.
If you feel picked on by mosquitoes, you may have good reason. One in ten people are very attractive to mosquitoes. Genetics are responsible for most of our susceptibility to mosquito bites. People with high concentrations of cholesterol on their skin attract mosquitoes. This doesn’t mean your cholesterol levels are high. It means these people may be more efficient at processing cholesterol and the mosquitoes are attracted to the byproducts remaining on the person’s skin.
Since mosquitoes prefer stagnant water, avoid ponds and lakes when possible and head for streams. Better yet, in mosquito areas take your water from streams and rest, cook, or camp away from water. This has advantages beyond avoiding mosquitoes. By avoiding heavily-camped areas, you’ll also have a more natural wilderness experience, and you’ll be more likely to avoid bears looking for your food.
Mosquitoes can be found at high altitudes. They’re usually not active below 55 degrees Fahrenheit. Mosquitoes don’t like moving air, so camping on a windy ridge can be a good idea. Mosquito populations and conditions can change drastically in just a few miles. You might get some good tips on where to hike and camp overnight from other hikers.
The most popular mosquito repellent continues to be DEET (N, N-diethyl-meta-toluamide) and for good reason. It’s been tested for many years and in many studies it’s been proven to be the most effective chemical repellent available. DEET was developed by the U.S. Department of Agriculture and was patented by the U.S. Army in 1946. It was registered for use by the public in 1957. About 38% of the U.S. population uses a DEET product every year. About 230 products containing DEET are registered with the Environmental Protection Agency. In addition to mosquitoes, it is effective in repelling biting flies, chiggers, fleas, and ticks. After completing a comprehensive re-assessment of DEET in 1998 the EPA concluded that insect repellents containing DEET do not present a health concern as long as consumers follow label instructions and take proper precautions. The bottom line is that DEET has a great safety record, and most problems reported are due to gross overuse.
All DEET product labels tell the consumer to: *Read and follow all directions and precautions on the label
*Do not apply over cuts, wounds, or irritated skin
*Do not apply to hands or near eyes and mouths of young children
*Do not allow young children to apply this product
*Use just enough repellent to cover exposed skin and/or clothing (More on clothing treatment with permethrin later, which will reduce the need for DEET clothing application to zero)
*Do not use under clothing (As above, there is no need to apply under clothing with the use of permethrin on clothing)
*Avoid over-application of this product
*After returning indoors, wash treated skin with soap and water (For hikers, it’s best to wash it off regularly so there’s no buildup)
*Wash treated clothing before wearing again (No need to use DEET. Permethrin is easier to use on clothing and very effective)
*Use of this product may cause skin reactions in rare cases.
For aerosol and pump sprays users are cautioned not to spray in enclosed areas and not to spray directly onto face. Spray on hands first.
DEET is approved for use on children over two months old with no restriction on the percentage of DEET. The American Academy of Pediatrics recommends the lowest concentration of DEET that’s effective for the amount of time you’ll be outdoors and to avoid repeated applications on children.
Most experts recommend concentrations of 20% to 35% DEET for adults over 12 years of age and concentrations of 10% or less for children under 12. The U.S. military uses the Ultrathon brand which is 34.34% DEET. It has been shown to be 99% effective for more than 8 hours and more than 95% effective for up to 12 hours depending on the conditions. It is dispersed in a polymer giving it a time-release action. The Centers for Disease Control reported:
*A product containing 23.8% DEET provided an average of 5 hours of protection from mosquito bites
*A product containing 20% DEET provided almost 4 hours of protection
*A product with 6.65% DEET provided almost 2 hours of protection
*Two products with 4.75% DEET were both able to provide roughly 1 ½ hours of protection
For complete protection there is not much of an advantage to increasing the concentration of DEET above 35%, and above 50% there is not an equivalent increase in duration of coverage. The brands with time-release formulas make it even more advantageous to use lower concentrations that are effective longer.
Length of protection from mosquito and other bites varies with the amount of active ingredient, temperature, perspiration or water exposure, and whether the repellent is rubbed off. In general, a higher percentage of DEET will last longer, although it varies between different products and brands. Different species of mosquitoes vary in reaction to the same repellent.
DEET’s most significant benefit is its ability to repel potentially disease-carrying insects and ticks. The Centers for Disease Control receives nearly 10,000 reports of Lyme disease (transmitted by deer ticks) and 1,000 reports of encephalitis, including West Nile (transmitted by mosquitoes) annually. Both of these diseases can cause serious health problems or even death in the case of encephalitis. Other diseases that DEET helps to prevent by repelling the host carriers are Rocky Mountain spotted fever, human granulocytic ehrlichiosis (HE), malaria, yellow fever, and dengue fever.
You should be careful when applying DEET because it can be damaging to plastics like eyeglass frames, watch crystals, leather, painted or varnished surfaces, rayon, spandex, and some other synthetic fabrics.
DEET can be applied to natural fibers and backpacking equipment made of nylon such as mesh netting, packs, tents, and sleeping bags. But it is easier, more effective, and longer-lasting to treat them with permethrin.
DEET can be applied with sunscreen, but there are some concerns and guidelines. Since the sunscreen will probably have to be applied more often, it’s best not to use a combination product, especially on children. The sunscreen protection level can be decreased by one third. The DEET can also be compromised, and possibly absorbed into the skin at a higher rate. Sunscreens are meant to work below the skin and repellents are designed to be an olfactory barrier on top of the skin. It’s best to apply the sunscreen first and wait a few minutes before applying the repellent.
Picaridin, or KBR3023, or Bayrepel outside the U.S. (trademark of Bayer AG), is recognized by the EPA as an effective alternative to DEET. Picaridin’s protection and duration are similar to DEET, and it has some advantages. It is colorless and nearly odorless, with a light, clean feel. It has low toxicity. It has been used worldwide and especially in Europe and Australia since 1998. It was approved by the EPA for use in the United States in 2005. The American Academy of Pediatrics has not yet made a specific recommendation for the use of picaridin on children.
Picaridin is effective in repelling biting flies, mosquitoes, chiggers, ticks, and fleas. It is environmentally friendly and will not harm spandex, rayon, or other synthetic clothing. It doesn’t damage sealants, coatings, or plastics such as watch crystals or eyeglass frames. Picaridin doesn’t need to be washed off after returning indoors. It is marketed in the U.S. under the brand name Cutter Advanced.
For areas where biting flies are a problem and are resistant to DEET, Sawyer Broad Spectrum includes 16% DEET and a separate fly repellent R-326 which repels flies, gnats, and no-see-ums. It is available in pump spray without alcohol.
Oil of lemon eucalyptus (p-menthane 3,8-diol or PMD), a plant-based repellent is also registered with the EPA and is available under the Repel brand name. It provides protection similar to repellents with low concentrations of DEET. Labels on these products warn that they are not to be used by children under 3 years. No other plant-derived repellents, including citronella, approach the effectiveness and duration of DEET or picaridin.
Avon Skin-So-Soft (IR3535) is recognized by the EPA as a repellent, but it is much less effective than DEET and is not long-lasting.
There is no scientific evidence that other methods such as taking large doses of vitamin B or eating garlic are effective in repelling mosquitoes.
As mentioned, loose-fitting clothing with tight-weave fabrics are great, but determined mosquitoes often find the parts of your body that are pressed tightly against the clothing. The greatest addition to fighting the mosquito war in recent years is permethrin. It is a synthetic chemical similar to the natural insecticide pyrethrum which comes from the chrysanthemum plant. Permethrin is approved by the EPA to spray on clothing, shoes, netting, and camping gear. When you use it on your clothing in combination with a DEET-based product on your skin you get complete protection from mosquitoes and many other pests. The U.S. Department of Defense uses this system. In tests conducted by the U.S. Army and Air Force, uniforms treated with a light .05% solution of permethrin gave 97.7% protection from mosquitoes. When used in combination with a 33% solution of DEET there was 99.9% protection over an 8 hour period. This test was conducted in an environment where unprotected people received 1,188 bites per hour.
DEET confuses insects. Permethrin kills insects or knocks them down when it contacts them or when they eat it. It has repellent effects also. It is effective against mosquitoes, ticks, flies, fleas, chiggers, mites, bedbugs, millipedes, centipedes, earwigs, spiders, ants, fire ants, and over 100 other insects.
To treat clothing, moisten both sides completely and allow it to dry. Apply it in a well-ventilated area. Permethrin is harmless to natural and synthetic fibers, even silk. It won’t harm Gortex. Permethrin is colorless, odorless, and non-staining. It doesn’t affect the feel of the clothing or gear. After it dries and bonds to the fabric in your clothing or gear it has exceptional resistance to sunlight, water, and heat. It bonds so tightly to the fabric that any chance for absorption through your skin is minimal. If any permethrin gets on your skin accidentally, it is rapidly inactivated and very poorly absorbed (less than 2%) and quickly inactivated by your skin and liver and excreted. Based on animal testing it is not expected to accumulate in the body.
No systemic effects have been reported. In EPA and FDA tests it was uncommon to have any skin irritation from permethrin. It doesn’t bond to skin as it does to fabric, and when it touches your skin it is deactivated in about 20 minutes. When applied to clothing by aerosol or trigger spray in the .05% concentration it will last up to two weeks or two launderings. Clothing sprayed or soaked in heavier concentrations will last even longer.
Hikers have always had the option of putting DEET on their clothing or gear, but it feels as though they’re applying something quite greasy when they do this. The DEET may feel enough like a lotion for use on your body, but adding it to gear hasn’t seemed practical because of the oily feel and because it doesn’t have a lasting effect. Permethrin doesn’t change the look or feel of the gear. Treating your tent netting and the tent in general has the obvious advantage of keeping pests farther from you. A permethrin treatment at the door of the tent can keep many varieties of crawling bugs away from you. If your pack is treated, you don’t have to worry as much where you place it at rest stops and around camp.
Studies report that permethrin is environmentally safe. It readily breaks down in most soils. Permethrin is tightly bound by soils, so there is very little leaching. It is nearly insoluble in water, and is not expected to leach or to contaminate groundwater. Permethrin degrades rapidly in water, although it can persist in sediments. Before it breaks down it is toxic to fish, so you should not use it near a water source or a drain. Permethrin is practically non-toxic to birds, but is very toxic to bees. There are some permethrin sprays specifically for dogs. These should never be used on cats because of their grooming habits and because they are much more susceptible to toxicity from permethrin.
If you receive mosquito bites there are a number of things you can try to reduce the itching and discomfort. Wash with soap and water and keep the area clean to avoid infection. A cool compress may be difficult when hiking, but if you’re near water or snow pack it can sometimes bring relief. Try a paste of baking soda and water, using just enough water to make the paste sticky, and apply it to the bite. Use calamine lotion or a topical anesthetic containing pramoxine, such as Caladryl. Take an antihistamine, one that is not very sedating to you. Topical steroid creams can be helpful. An anti-inflammatory drug such as ibuprofen or naproxen may reduce swelling. Ibuprofen is probably already in your arsenal for muscle aches. Other anti-inflammatory choices are oral evening primrose oil and papaverine. Try a 1-percent hydrocortisone cream. There are many home remedies that are not scientifically proven, but are interesting. Choices include applying soap, deodorant, toothpaste, rubbing alcohol, Visine, Murine, or vinegar.
With a little precaution, you can have total protection from mosquitoes and ticks. Spray your clothing and gear ahead of time with permethrin and when you hike cover your exposed skin with a DEET-based repellent.