Beware of Poison Ivy!

by Forrest M. Mims III

Spring means the beginning of poison ivy season across much of the United States.

The El Nino winter from which we have emerged must have provided just the right growing conditions for poison ivy. The plants along Geronimo Creek appear healthier than ever.

Poison ivy (Toxicondendron radicans), poison oak (T. diversilobum) and poison sumac (T. vernixare) all capable of causing severe rashes in many people. The dominant poison plant here at my sun and sky observing site in South-Central Texas is poison ivy.

The sap of these poisonous plants contains an oil called urushiol. Contact with a few millionths of a gram or so of urushiol may be enough to trigger a rash in people allergic to it. And most people are. According to the American Academy of Dermatology, some 85 percent of the population is allergic to urushiol.

My reaction to poison ivy ranges from nothing to a brief burning sensation accompanied by a slight reddening of the skin that lasts an hour or so. Those who are much more allergic can experience severe skin rashes and blistering.

The best way to avoid a poison ivy rash is to stay away from the plant. But that’s not possible if you have pets that walk through the stuff and collect urushiol on their fur. Should you pet the animal, some of the urushiol will be transferred to your skin.

You can also get a poison ivy rash by touching clothing, tools and implements that have come in contact with it. Soccer balls, base balls and golf balls can collect urushiol if they roll or fly through a poison ivy vine. You can even get a rash by touching poison ivy vines that have long been dead.

An especially dangerous combination is smoke loaded with poison ivy fumes. It’s very important to never burn the vines and to stay well away from brush fires that may be consuming poison ivy.

Be sure to study the nearby photograph if you are not sure how to tell a poison ivy plant from a box elder. The latter resembles poison ivy from a distance but is entirely harmless.

The three leaflets of poison ivy are an attractive shade of green. Plants can grow individually or in patches. Small plants emerging at intervals from underground roots do not look like vines. Mature vines can be as thick as your wrist and climb 50 or more feet into a tree.

There are many articles about poison ivy on the web and at the library. The American Academy of Dermatology has a copyrighted brochure about poison ivy and its effects.

Should you contract a rash, try calamine lotion. If the rash is severe, consult your pharmacist or physician.

Forrest M. Mims III and his science are featured online at www.forrestmims.org.

This feature was originally published in Forrest Mims's weekly science column in the Seguin Gazette-Enterprise, Seguin, Texas. The column is written for a general audience.