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Q: I'm seeing patients with all the classic signs of allergic contact dermatitis: an itchy rash, sometimes oozing, with occasionally painful blisters on their hands, arms, and legs. What's making the dog days of summer so uncomfortable for them?

  
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A: Scratch the surface and you'll find one of the usual suspects at work: poison oak, poison sumac, or poison ivy. The cause of the contact dermatitis you've described is urushiol, a sticky, clear oil contained in the sap of these plants.

 

A day or two after exposure, the skin starts to redden and become itchy. In another day or two, tiny blisters (intraepidermal vesicles and bullae) appear. Some swell, burst open, and ooze for up to 4 days. It can take up to 4 weeks for the reaction to completely subside.

 

It may be possible to stop the rash before it starts by washing thoroughly with soap and water or rubbing the skin with isopropyl alcohol. But better be quick about it: Some sources say this must be done within an hour of exposure; others claim the window of opportunity is a scant 10 minutes!!

 

Direct contact with a poisonous plant isn't the only way to get the rash. Urushiol can infiltrate your patient's world via gardening tools, clothing, and pets, so he should be prepared to thoroughly wash anything that may have been exposed. Advise him to avoid burning these poisonous plants because of exposure to the toxin in the smoke.

 

Bad to worse

Some patients can have a more severe reaction to urushiol than others. After exposure, their immune system launches an attack that can trigger a dangerous anaphylactic response. This response is marked by airway constriction, a drop in blood pressure, widespread tissue swelling, heart rhythm abnormalities, and in some cases, loss of consciousness. This medical emergency must be treated promptly with epinephrine.

 

Some patients who are less susceptible will have a reaction that's milder but still serious. They should seek medical care if they have large areas of rash and significant discomfort; a rash affecting the mouth, eyes, or genitals; an area of rash that develops infection; or significant swelling.

 

For less severe reactions, a cool soak in the bathtub followed by application of an over-the-counter (OTC) topical corticosteroid (like Cortaid and Lanacort) generally soothes the irritation from the rash. An OTC oral antihistamine like diphenhydramine (Benadryl) can also help.

 

For more severe cases, the patient may need prescription oral corticosteroids. Advise the patient that the drug must be taken for at least 14 days and preferably for 3 full weeks. If the drug's stopped prematurely, the rash can rebound with even greater severity.

 

Remind patients to take Ben Franklin's words to heart: an ounce of prevention is worth a pound of cure. To avoid exposure, they should wear long pants, shirts with long sleeves, and if possible, gloves and boots when hiking or gardening.

 

One more thing: That "leaves of three" rule doesn't always apply. Some plants have leaves in groups of five to nine!!

 

Learn more about it

 

Allergy: Poison ivy, oak, and sumac. http://www.emedicinehealth.com/articles/8435-1.asp. Accessed May 10, 2005.