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

AGE, EXPOSURE -- NOT CASHEWS -- REDUCES POISON IVY SENSITIVITY

Question: I know that summer is approaching because I have poison ivy again. As a child I had severe reactions to it. My eyes would be swollen shut, I'd have blisters on my hands and arms and generally be miserable. Now, I only get an occasional small area that quickly heals. I think that this may be because I eat cashews. I've read that they contain small amounts of an oil similar to the rash-causing oil in poison ivy. Thus, eating the nuts builds up my immunity. My wife, who tends to take a skeptical view of natural remedies, thinks I have less trouble now because I spend less time in the woods. What do you think?

Answer: I've been happily married for more than 30 years and have learned a few things about relationships in this time. When my wife thinks something I've said is silly, I pay attention. I do this for two good reasons. First, she understands the way I analyze a problem. Second, she has a good head on her shoulders and, therefore, she may have figured out something I've missed. That said, I think your spouse probably has a valid point about your diminished exposure to poison ivy reducing both the frequency and severity of episodes you experience.
Poison ivy and its close relatives, poison oak and poison sumac, cause itchy blisters in about 85 percent of those who are exposed to them. So, your life-long unfriendly relationship with poison ivy is actually not that uncommon. To get a little more technical, the rash is actually caused by exposure to a plant chemical called urushiol. This "natural" chemical is the sticky sap found within poison ivy's leaves, stems and roots.
The human immune system requires a primary exposure to an offending allergen -- in this case urushiol. This first exposure doesn't produce a rash, but it prepares the immune system to respond to subsequent exposures. The next "brush" with the plant brings about a profound allergic response that you clearly remember from your childhood poison ivy episodes. Each additional exposure, if it occurs relatively soon after the previous one, will result in a similar or a more dramatic rash.
The allergic response of children is generally more intense that it is in adults. By this alone, I would expect you to have somewhat less trouble now than you did a decade or two ago. Also, your immune system may have become less "trigger happy," since you have gone several years without a large outbreak of poison ivy rash.
Cashews do contain an oil that is similar to urushiol. Individuals who are very sensitive to poison ivy can have a reaction to eating these nuts. Typically, a "cashew allergy" produces a rash around the mouth and may cause an upset stomach. Eating cashews can even trigger asthma in severely sensitive people.
There is no medical evidence that consuming small amounts of an allergic substance produces desensitization to that item in the way allergy shots do. Instead, it is more likely to sensitize (that is, "rev up") the immune system. Several years ago a well-known natural foods advocate recommended eating three poison ivy leaves every week starting from the tiniest buds in the spring and continuing as the plant grows. Thus the person was consuming progressively large doses of urushiol. By the time summer is in full swing the large leaves were supposed to provide immunity to poison ivy. Didn't work! Instead, it caused lots of misery for poison ivy sufferers.
The only good prevention for poison ivy is to keep the urushiol off your skin. This can be done by avoiding the plant, by wearing protective clothing or by applying a flexible protective barrier cream when your risk of exposure is high. Promptly washing with soap and water after exposure also decreases the risk that you will actually get a poison ivy rash. If you're unsure of the appearance of poison ivy, oak and sumac in its various growing conditions, you should point your Web browser to: http://res.agr.ca/brd/poisivy/title.html.

"Family Medicine" is a weekly column. To submit questions, write to John C. Wolf, D.O., Ohio University College of Osteopathic Medicine, P.O. Box 110, Athens, Ohio 45701. Past columns are available online at http://www.FamilyMedicineNews.org.