ASK DR. BAUGHAN                                                         May 22, 1998

BUG DOPE REVISITED

For anyone who has spent five minutes outside in the past week, it is painfully evident that ‘THEY ARE HERE.”  I am referring to black flies, not tourists or aliens.  Even though I wrote about insect repellents last August, some new information has come to light that I wanted to share since this will be a peak time for people to be buying and using various chemicals on their bodies.

This information concerns DEET (diethyltoluamide), the most common ingredient in commercial insect repellents.  DEET has been around in public use since the 1950s.  The manufacturer’s claim to safety is that it has been used by millions of people annually for decades without apparent epidemics of disease or death.  Scattered reports appear periodically concerning seizures in children.  The more we learn about the physical and chemical properties of DEET, though, the more cause for concern I find.

A little chemistry:  a ring of six carbon atoms joined by double-bonds is called a benzene ring.  Benzenes are very carcinogenic to animals and humans.  Toluene is a variation on a benzene ring that is also toxic.  DEET (diethy - toluamide) is a variation on a toluene ring.  Now a variation on a variation does not equal a smoking gun for cancer, but it warrants careful attention.  What happens when this is sprayed or rubbed on people?  Sixty-percent is absorbed through the skin.  It then is spread throughout the body by the circulatory system.  It is readily stored in the body’s fat stores, where it may be stored or slowly metabolized for a long period.  It also can easily pass through what is called the “blood-brain barrier,” meaning it gets into and can be stored in the brain.  So in addition to immediate reactions, there is concern for long-term effects that become harder to study.  I hate to raise alarms without conclusive evidence, but if you wanted to find a frequently used chemical with potentially nasty properties, DEET would fit the bill.  The FDA has recently taken the step of limiting the percent of DEET that can be in products marketed for use in children to 10%, which is getting low enough that black flies might consider it a seasoning rather than a repellent.

Another feature of DEET that makes me uncomfortable:  spray it on plastic, spandex or polyester sometime.  Then watch the material deform or melt.  I don’t think I want that in my brain or liver.

What other choices do we have?  Permethrins will be the major alternative, and some manufacturers of repellents have already or will soon be offering permethrin products along with or instead of DEET.  So read labels.  Permethrins are derived from chrysanthemums, so there are no benzene rings to worry about.  They do not penetrate the skin.  In fact, one of their drawbacks is that they do not stick to skin well.  But they stick to hair and clothes very well.  They also act as an insecticide, not just a repellent.  The vapor from clothes or hair has an envelope of protection around the other parts of the body, although the effect may be insufficient at the beach or whenever a person is in a bathing suit.  For campers, hikers, cyclists and other other athletes who aren’t naked, though, permethrins can have a prolonged effect.  Permethrin powders can be added to the rinse cycle of clothes and last through up to six washings.  Sprays can last on clothes or tents  or sleeping bags for days.  And they won’t dissolve the tent.

Avon’s Skin-So-Soft and citronella oils do have some effectiveness, but keep them handy.  They need to be re-applied almost hourly to give protection.

So please enjoy the beautiful outdoors but consider the safety of the chemicals you use.