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Treating Caterpillar-Rash

By Jason Poquette, BPharm, R.Ph
Literary caterpillars, like the hookah-smoking blue caterpillar in Alice’s Adventures in Wonderland, may be quite amusing.  But the recent outbreak of caterpillars across New England has been anything but entertaining, and even has some patients heading for the doctor.  If you have been outdoors at all in the past month or so you have probably seen some of these caterpillars falling from the trees onto your clothing and skin.  For some, contact with the fine hairs protruding from these caterpillars can cause a blistering rash, itching, eye irritation and difficulty breathing.

It isn’t too often that I talk to patients in the pharmacy about caterpillars.  Several newspapers here in the Northeast said that even the New England Journal of Medicine is speaking up on the issue, calling it the worst infestation in the area since 1981.  A physician from the East Providence Allergy and Asthma Center, Dr. Russell Settipane, told reporters that patients should be cautious about contact with these caterpillars, because “the little hairs on the caterpillar can stick to the skin, causing a histamine-type reaction.”

There are actually at least 2 types of these caterpillars (the brown tailed moth caterpillar and gypsy moth caterpillar) currently climbing the trees and falling like rain being reported on at the moment.  They look similar, but can be distinguished by the dot pattern on their backs.  Both can cause damage to trees and allergic reactions to individuals sensitive to them. 

Of course, the rash isn’t anything new with this most recent crop of caterpillars.  Several years ago the Maine Forrest Service along with the state’s Department of Health and Human Services produced a public service document entitled “Browntail Rash” educating the public about the nature of this allergic condition which can be quite irritating.  To quote from their document:

“The caterpillars are active from May through July but the dermatitis is most common in late June and July when the toxins reach their highest concentration in the mature caterpillars. The signs and symptoms of the dermatitis can develop at the time of the exposure or be delayed for several hours. Most individuals developing the dermatitis will do so after outdoor activity which exposes them to trees or shrubs harboring this pest. Severe rashes have developed after contact with clothing which became impregnated with windborne hairs while being dried out-of-doors. The duration of the rash varies from hours to days.”

A forest entomologist, Charlene Donahue, talked to newspaper reporters last year warning that this year was likely to be a bad one for these moths.  The dry spring meant less of the mold that typically deters the spread of this species.  “We’re going to have a lot more Brown Tailed Moths next spring,” she said.  “I would prepare for a bad year next year.”  She was right.

So what should people do?  Not everyone reacts badly to the fine hairs which cover these caterpillars.  And direct contact isn’t necessary for irritation or breathing difficulty to develop.  The hairs, of which there might be upwards of 2 million on a single caterpillar, are fine enough to become airborne and make contact with our skin or be breathed in.  Whenever possible, avoiding areas of heavy infestation is the best advice. 

After potential exposure to these caterpillars it is recommend that you take a cool shower and change your clothing.  Drying clothes inside might reduce outside exposure of the drying clothes to airborne hairs.  If you’re experiencing one of those “blistery, oozy” rashes that are sometimes reported consider treatment with a cool compress and calamine lotion.  Oral diphenhydramine (e.g. Benadryl®) capsules can help reduce itching but will likely cause drowsiness.  Difficulty breathing or more severe rashes on the face or near the eyes should be seen by your doctor.

So keep an eye out for these critters and keep your distance if you suspect you might be sensitive or have an allergic reaction.   It might be fun to meet a talking caterpillar in Wonderland, but here in New England these creatures could result in a not-so-fun adventure to your local pharmacy for relief.