FAMILY MEDICINE® COLUMN
By John C. Wolf, D.O.
Associate Professor of Family Medicine®
Ohio University College of Osteopathic Medicine

PASSAGE OF TIME LESSENED READER'S SENSITIVITY TO POISON IVY

Question: When I was in first grade, some of the boys thought it was fun to take leaves, place them between our thumbs and blow on them to make a sound. The leaves that made the best noise were ones on a vine growing up a tree in the playground. It turned out, unfortunately, to be a poison ivy vine, and I ended up with a very bad case. My eyes were swollen shut, and I had to stay home from school for several days during the worst part of the outbreak. For years after that, I only had to look at poison ivy from a distance to break out. Over the last 15 years, or so, I've noticed that I seem to be less sensitive to this horrible weed. I've even brushed up against it, not washed my skin for several hours and not developed a rash at all. How would I lose my allergy to poison ivy after being so super sensitive for so many years?

Answer: Your observations point out important features of the human defense system. Your exposure to poison ivy or more accurately, exposure to the chemical urushiol that is found within poison ivy's leaves, stems and roots is what actually produces the allergic reaction causing the rash. The first episode was a sensitizing dose of the allergen. Once sensitized, the body can then react to even a very small exposure to the offending item. That is why you only needed to "look at poison ivy" to get it for years afterwards. With the passage of time, the body can become less sensitive, just as you have noted.

Every summer, I see quite a few people with extensive poison ivy as a consequence of their belief they can't get it. Most get it while pulling weeds or playing in the grass. The worst cases, however, occur to those who have been using their "weed whacker" while wearing shorts. Please don't ever do this. It is no fun being covered from ankles to thighs with itching blisters.

In order for urushiol the "poison" of poison ivy to get on your skin and produce a rash, the poison ivy plant must be broken. This is the reason that an allergic person can sometimes brush up against a healthy poison ivy plant and not break out, just as you have noted.

Once the chemical comes in contact with the skin, it begins to penetrate within minutes, but it takes from 12 hours to several days for the "poison ivy" to appear in sensitive individuals. First there is itching, redness and swelling, followed by blisters. And contrary to myth, poison ivy can't be spread by touching the oozing liquid in the blisters!!! This liquid is not urushiol, but your body's own fluid produced as part of its reaction to urushiol. But as you know, poison ivy can be spread.

If the victim gets urushiol on his or her hands, touching another part of the body -- or another person's body can transfer the chemical to that area. That's the reason poison ivy tends to turn up all over the body, even though the plants generally only come in contact with the exposed areas of the skin.

The area which has the greatest exposure to the urushiol will usually break out first. Areas which have thick skin or less urushiol on them will then break out a day or two later, giving the impression that the poison ivy was spread from the first group of blisters.

If you suspect that you have been in contact with poison ivy, or its cousins poison sumac or poison oak, the first thing to do is to thoroughly wash with soap and water. Any clothing that has come in contact with the sticky sap should also be washed promptly. Handle the clothes carefully, preferably with gloves, to prevent any more skin contact with the sap. If more than 20 minutes has elapsed since the exposure, washing may not prevent the initial rash, but it can prevent you from spreading it further.

Family Medicine® is a weekly column. To submit questions, write to John C. Wolf, D.O., Ohio University College of Osteopathic Medicine, Grosvenor Hall, Athens, Ohio 45701.