ASK DR. BAUGHAN                                                         August 28, 1997

THE DOPE ON BUG DOPE

The French may be experts on the subtle distinctions between wines.  Eskimos may be able to differentiate dozens of types of ice and snow.  Residents of Mt. Washington Valley become connoisseurs of insect repellents.  After the snow melts in May until the last leaf drops in November, to enjoy the outdoor beauty of the region requires sharing it with tenacious and blood-thirsty little critters.  This requires an ecological decision with four basic choices: (1) become a blood donor for insects (2) stop bathing (3) dress in the latest in designer net-ware (4) use chemicals.

I am indebted to an excellent review of currently available chemical repellents in the August 1997 issue of Postgraduate Medicine by Erick Mafong, M.D. and Lee Kaplan, M.D.  There are four primary substances on the market that have systematic evaluations of effectiveness in protecting skin from biting bugs.

DEET (diethyltoluamide) is the most widely used repellent in commercial products (Cutter, OFF!, Repel, etc.) and varies in concentration from 10% to 100%.  It was developed in 1953 for use in the US military and marketed to the public in 1956.  It is used by an estimated 100 to 200 million people annually.  It has been shown to be the currently most effective repellent against blackflies, midges, mites, and chiggers.  How long it lasts may depend on how much the person sweats, how much rubbing of clothing occurs, and to some degree, how oily or dry a person’s skin may be.

The main concern expressed about DEET is its safety.  A review of the medical literature shows infrequent to rare reactions to DEET.  A review of 9000 calls related to DEET to poison control centers found only 4 serious accidental cases.  In 1979, there were 6 reported cases of seizures in children aged 1-8 years old.  In 1989, another 5 cases were noted by the Centers for Disease Control.  A few other reports documented that DEET is toxic if you drink it.  Risks to children can be minimized if the lower concentrations (less than 10%) are used on skin and if skin can be protected by clothes as much as feasible.  Even in adults, there is little demonstrated benefit in preparations over 50%.  DEET works well if applied to most clothing, although it may damage rayon, spandex and polyester.

Permethrin is more effective than DEET in repelling ticks.  It is the ingredient in Permanone, Coultston’s, and Duranon.  It is the active agent in Elimite and Nix preparations used to treat scabies and lice.  It works better when applied to clothing and may last through several washings.  Fortunately, we still have few cases of Lyme disease this far north because the tick that carries it does not thrive up here, but for outdoor activity in endemic areas, use permethrin.

Avon’s Skin-So-Soft is used widely as a repellent although it was originally developed as a skin softener.    When compared with a 33% DEET liquid with US troops in Honduras, it provided a respectable 71% protection versus 96% for DEET.  It seems to work by forming a slippery barrier between the skin and the insect.  It needs to be used fairly often;  most studies show loss of effect after 60 to 90 minutes.

Before DEET came along, citronella was the most popular repellent.  It is a fragrant, volatile oil from the leaves of Cymbopogon grasses native to tropical Asia.  Citronella oils have shown 96% effectiveness, again for limited times, when applied to skin.  Citronella candles may provide 42% protection against bites, but these studies get harder to evaluate because there are so many variables, such as distance from the candle, wind, etc.