Wilderness Underfoot: Poisonous triplets

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StoryImage( ‘/Images/Story//Auto-img-111885682910946.jpg’, ”, ‘Noxious sap – Poison ivy (top), poison oak (center), and poison sumac (bottom) are members of the cashew family –Anacardiaceae – which includes an odd assortment of cousins, such as: pistachio trees, mango trees, pink peppercorn plants, and sumacs. The poisonous triplets of this family all occur in our region, but poison ivy seems to be the most frequent cause of allergic reactions here. Both poison ivy and poison oak can be recognized by their woody vines and leaflets in clusters of three. The leaves are irregularly lobed, especially on the poison oak (named after the resemblance to oak leaves). Poison sumac is harder to identify. It has rows of leaves (not sets of three) and it resembles other sumacs that are not poisonous. Although these three plants are poisonous to humans, they seem to be harmless to all other animals. Deer and other mammals eat the leaves, twigs and berries. Quail, grouse and turkeys also feed on the berries.’);

Poison ivy, poison oak, and poison sumac are notorious for the irritating rash they cause. Some people believe they can be contaminated by airborne vapors around these plants, but this is a misconception. The poison isn’t airborne unless the plants are burned – sooty smoke released during burning is dangerous to your skin, your lungs and the lining of your throat.

Physical contact with the sap is the cause of the allergic reaction that leads to an itchy rash. The sap is easily transferred from one surface to another, so garden implements, shoes, clothing and pet fur can contaminate you long after contact with the plants. In fact, the sap may cling to objects for as long as five years and still cause an allergic reaction when touched. The plants are poisonous whether dead or alive.

The cause of the allergic reaction is an oil in the sap called urushiol. Just a billionth of a gram of this oil can cause a reaction. But to do so, it must penetrate the outer layer of skin, the epidermis. After a complex bit of bonding with skin proteins, these altered proteins are no longer recognized by the immune system, which sets off an aggressive attack. The rash, itching and inflammation are the result of an overreaction by the immune system.

Urushiol oil takes longer to penetrate thick skin than thin. Washing off the sap soon after exposure – especially within the first hour – can limit or prevent a reaction. It may take more than a day or two before a reaction occurs, and then the rash takes as long as two weeks to clear up. Once an allergic reaction has started, there’s no real danger of spreading the infection through contact with the rash (such as scratching); this is just another misconception. Some prescription and over-the-counter products may help to alleviate the irritation.

From the June 15-21, 2005, issue

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