Poison Ivy

By John Jentes, M.D., QCare Physician
Located in the Hillcrest Medical Building
350 Hillcrest Drive
Ashland, Ohio 44805


Like the movie, True Lies, there are things about poison ivy that are "true" and things that are "lies" - or more correctly - misconceptions. Let's explore some.

First TRUTH: when someone comes in contact with a plant of the Rhus genus (poison ivy, oak or sumac) it is likely that they will get some oily resin, urushiol (u-ROO-she-ol), on their skin. Depending on how long the resin remains on the skin and other factors, the resin can penetrate the surface of the skin and cause an allergic reaction in the form of a rash. The rash usually begins within 12 to 48 hours after resin exposure. The rash can be in the form of small patches of redness, to dry bumps, to blisters - sometimes very large ones.

First LIE: You can "catch" poison ivy from someone who has blisters and the blister fluid gets on you. (A similar misconceptions is that the blister fluid can spread the rash to other areas of the body.) The fluid in the blisters is serum - it does NOT have the urushiol resin in it. Therefore it can't spread the rash to anyone else or to other parts of the body. The rash may appear to be spreading. However, this is because the concentration of resin on different body areas may vary and different areas of the skin react to the resin differently. It's not spreading from the fluid from the blisters.

Second TRUTH: You can, however, get poison ivy without actually coming in contact with the plant. The resin can get on your pet's fur, for example, and when you touch the fur, you can pick up the resin. If someone else has the resin on them or their clothing and you come in contact with that resin, you can get a reaction. Likewise, some folks are sensitive enough to the resin that if someone is burning the plants and they come in contact with the smoke which contains the resin, they can have a reaction.

Second LIE: Perhaps you've heard something like this: "My aunt Tillie can roll in the stuff and never get it and all I have to do is walk past it and I'll get it." It's not possible to "walk by poison ivy" and get the resin on your skin. You must, in some way, get the resin onto your skin. It does appear to be true that there are people - perhaps up to 30% of the population, who are less sensitive to urushiol, and not react when they come in contact with it. It is still wise to avoid contact with poison ivy since reactions can develop after repeated exposures.

Third TRUTH: The best defense is to avoid the plant altogether. The old stand-by "leaves of three let them be" is still good advice. If you must be around these plants, even if you think you're not allergic to urushiol, it's best to wear protective clothing when doing so. If you come in contact with them anyway, the FDA recommends cleaning the exposed areas with rubbing alcohol first, as this apparently deactivates the resin. Next, flush with clean water and finally wash with soap and water. Be sure to also wash exposed clothing, work gloves, etc. and take care to wear protective gloves when handling the resin covered clothing.

Third LIE: The urushiol resin evaporates quickly with exposure to the sun and therefore doesn't stay on objects for very long. I even believed this one for awhile, but according to mayoclinic.com, "uroshiol can remain allergenic for years". This can explain why some folks get reactions in winter, when most plants are long gone. Many will contact it from burning wood that had ivy on it. They will come in contact with the smoke, or from handling the wood itself.

Last TRUTH: Once a reaction starts, treatment depends on how troublesome it is. If minor, even left untreated, most reactions will resolve on their own in one to three weeks. If the reaction is in the patchy or bumpy stages, it can be treated with a variety of over the counter medications including topical cortisone creams and oral antihistamines for itching. I generally do not recommend topical antihistamines or topical numbing creams for poison ivy. If, however, the reaction is in the blister stage, it often needs treated "from the inside out" with oral steroids or a steroid injection.

Last LIE: "I can take "poison ivy pills" and build up my immunity so I won't get it." To the best of my knowledge, there are no products currently available that have been proven, in reputable studies, to develop urushiol immunity.