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Things You Might Not Know About Poison Ivy

Posted by Dr. Claire McCarthy  June 19, 2013 09:36 AM

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poison ivy.jpgJust the other day, a mother told me that her husband took the kids for a hike--through a whole bunch of poison ivy. 

"So far, no rashes," she said. "I keep checking."

And she does need to keep checking--because the rash can show a week or longer later (usually with a first exposure), something this mom knew but lots of people don't.

I've found that there are lots of other things that people don't know about poison ivy. Here are a few:

There are different kinds of poison ivy--and it can look different at different times of year. The adage "leaves of three, let them be" simply won't keep you away from everything that can give you a poison ivy rash. The plants grow all over the US, so they are hard to avoid. The Poison Ivy, Oak and Sumac Information Center has lots of pictures.

You don't have to touch it to get the rash. The toxin in the leaves, urushiol, escapes whenever the leaves are broken or bruised--and the toxin can get on things, like gloves, garden tools, and clothing. it can even get into the air if the stuff gets mowed or plowed. This is why...

You can get the rash from people or pets. If they have been the toxin on them, when you touch (or pet) them, you can get it too. Just to be clear: you can't get the rash from someone's rash--it's not contagious that way. It's the toxin from the plant that gives you the rash.

The best thing to do is to wash immediately. Take off any contaminated clothing, and wash with mild soap and water--as soon as you can. That's the best thing you can do to get at least some of the urushiol off your skin, and make a reaction less likely. Remember to clean under nails, too.

There are various different rashes you can get from poison ivy. You can get bumps, scales, and various sizes of bubbles and blisters. Often they will be in a line or streak, showing where the plant touched the skin. However the rash looks, it's usually red (although it can have black spots when the toxin stays on the skin and oxidizes)--and usually itches like crazy.

Treating the itch is all you usually need to do. Simple stuff, like oatmeal baths or cool compresses, can make a real difference. Anti-itch preparations that have menthol or phenol, like calamine, can also help--as can Burow's solution or Domeboro. Interestingly, antihistamines like Benadryl don't help all that much because of the way urushiol causes itching. Steroid creams may help if used early, but once there are any bubbles or blisters, they don't help much.

Sometimes you need to take steroids--and if you do, you need to go off them slowly. In severe cases, taking steroids by mouth is needed--but if you do take them for just a few days, like we often prescribe in asthma, the rash can come back. So the recommendation is to lower the dose bit by bit over two or three weeks.

If you're ever not sure about a rash, your doctor is your best resource. You should also call your doctor if a rash you think is poison ivy is on the face or genitals, is getting worse, gets very swollen or has pus coming out of it--and you should call if there is fever or the person with the rash seems ill.

Hope your summer is poison-ivy-free!

Is there something you'd like me to write about? Leave me a message on my Facebook page--and "like" the page for links to all my MD Mama blogs as well as my blogs on Thriving and Huffington Post. 

This blog is not written or edited by or the Boston Globe.
The author is solely responsible for the content.

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About MD Mama

Claire McCarthy, M.D., is a pediatrician and Medical Communications Editor at Boston Children's Hospital . An assistant professor of pediatrics at Harvard Medical School and a senior editor for Harvard More »

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