How to avoid mosquito bites – DEET Repellents Must Be Used With Care

Originally published in The Ottawa Citizen June 22, 2002
Original Title: Don’t Let the Bugs Bite!

Every summer our skin is subject to the mosquito onslaught. Young children’s skin tends to react more strongly from bites. A young child’s immune system has not had the pleasure of the hundreds of times adults have been exposed to mosquito saliva. With age we develop antibodies so that by adulthood our response to these bites is more subdued.

Clinical complications to common North American mosquito bites are infrequent. Complete eyelid closure due to swelling commonly occurs in small children. Similar dramatic swelling of the face can also occur. Eyelid swelling does not often lead to infection. Lymph nodes in the neck can swell in response to scalp and facial bites that can persist for several weeks.

A few simple precautions can help avoid mosquito bites. The skin should be covered with protective clothing such as long pants and long-sleeved shirts. Children’s play areas (such as a sandbox) should be placed in open sunny areas (remember sunscreen use) and not near vegetable gardens, brush or trees. Most bites occur in the early dusk or early dawn.

DEET (N, N-diethyl-meta-toluamide) is one of the most effective commonly used topical insect repellents. In 1946, the U.S. Army developed it for use in insect-infested areas. It was made available to the general public in 1957. Although the exact ingredient or combination of ingredients that repel mosquitoes and ticks is unknown, it is likely to be toluene. Toluene is an organic solvent used in rubber and plastic cements and paint removers. DEET belongs to this family chemical family.

DEET is absorbed through the skin. Since children have a greater body surface area to weight ratio the side-effect risk is greater. Although toxic encephalopathy (brain poisoning) and seizures are associated with its use in children, these rare instances occurred with prolonged exposure to DEET. Swallowing DEET can be fatal. Coma, seizures and hypotension (low blood pressure) occur within an hour of ingestion.

Rashes, hives, blisters, skin and mucous membrane irritation and numb or burning lips tend to be more prevalent with DEET concentrations of 50 to 75% or when used in excessive amounts. There is no evidence that it causes cancer or birth defects.

Commercial preparations are available as sprays and rub-ons. Although comparative studies show only moderate advantage, the effectiveness of each is partly related to the concentration of DEET. A combination of clothing sprayed with an insecticide (NIX) or an odour repellent plus DEET applied to exposed skin surfaces appears to be the most effective bite protection available.

Due to the toxic side effects of skin absorption, DEET concentrations of less than ten percent or none at all should be used directly on children’s skin. Adults should not apply concentrations greater than 30% onto their skin.

DEET sprays should be applied to children’s clothing before they are worn. Entomologists wear a special mesh jacket that is placed in a Zip-lock bag with DEET for two hours. Greater concentrations of DEET can be used in this case. It can be worn over clothing and is effective for many days. Skin absorption is minimized because of the avoidance of direct skin contact. DEET can damage some synthetic fabrics and plastics.

DEET should not be applied to the skin during pregnancy.

Children should not apply DEET themselves. Parents should apply it to their own hands then put it on the child avoiding their face, hands, open sores or cuts. Prolonged or excessive use of DEET, application in enclosed spaces and failure to wash off the repellent once indoors can increase the risk of side effects.

Mosquito coil smoke contains about 70 different volatile organic compounds including allethrin, phenol, benzene, toluene and xylene. Animal studies with long term exposure (8 hours a day, 6 days a week for 60 days) to mosquito coil smoke showed metaplasia (abnormal growth) of skin cells, poor weight gain and lung damage. It should therefore not be used in enclosed or poorly ventilated areas.

Avon Skin So Soft bug repellents contains citronella oil (0.05 to 0.10 %); a safer alternative having less potential toxic effects. It has a very acceptable odor and appears to adhere to the skin better.

Citronella is a volatile oil derived from obtained from the leaves and stem of the plant Cymbopogon winteratus. Used for over 50 years as an insect and animal repellent, it is found in many familiar insect repellent products: candles, lotions, gels, sprays and towelette wipes for use on clothing and people. Citronella is also present in some home lawn and garden pellet products to repel dogs and cats. When used as directed, citronella products are not expected to cause harm to humans, pets or the environment. These repellents are not as effective as DEET and provide about 30 to 40 minutes of protection from bites.

Proper use of these products will minimize any potential for harm and keep the bugs out of your hair.

Product DEET % Toluamide (%)
Off Skintastic lotion 7.125 0.375
Off Skintastic for kids spray 4.75 0.25
Muskol with sunblock 15 9.5 0.5
Deep Woods Off 95.0 5.0
Muskol Spray 23.75 1.25
Muskol 8 hour lotion 28.5 1.5

© Dr. Barry Dworkin 2002

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