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How Do You Get Poison Ivy And How Do You Get Rid Of It?

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First contact will not cause a rash, but it sensitizes the person to the irritating substance.

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The Tampa Tribune

Published: November 6, 2008

By RICHARD F. LOCKEY, MD

Tribune correspondent

You hear more about poison ivy, but poison sumac and poison oak are also plants that when touched can cause the annoying, itchy rash known as allergic contact dermatitis. While certain allergies, such as hay fever and allergic asthma, may be inherited, no genetic predisposition is needed to develop the skin irritation caused by poison ivy and its cousins. Poison ivy reactions are caused by an abnormal immune response involving a type of white blood cell, whereas hay fever and allergic asthma are caused by a molecule that attaches to inflammatory cells in the nose and lungs and triggers an immediate allergic reaction.

The poison ivy rash is triggered when the plant's leaves or stems brush against the skin while a person is hiking, camping, working in the yard or engaged in some other outdoor activity. The skin may absorb some of the oily resin made by the plant. First contact will not cause a rash, but it sensitizes the person to the irritating substance. When the next exposure occurs weeks, months, or even years later, a very itchy red rash appears several days later where the toxic plant contacted the skin. The rash itself is not contagious, but severe reactions may develop in those who are highly sensitive, including swelling and widespread oozing blisters. Poison ivy also may be transmitted by indirect contact - for instance, when you touch clothing, pet fur, sporting gear or other objects that have come into contact with one of the plants.

The best way to prevent an allergic reaction is to learn to identify poison ivy and similar poisonous plants and stay clear of them. When you cannot avoid contact, wearing long pants, a long-sleeved shirt, socks and gloves may help protect your skin. If you think you've come into contact with poison ivy, immediately remove your clothing, take a shower, and wash your clothing promptly. Washing removes the plant's oil from the skin and clothing, and may help avoid a reaction. The rash usually does not appear until 24 to 72 hours after contact, because it takes time for the white blood cells that cause the rash to migrate to the skin and set off the reaction.

Cool compresses, calamine lotion and over-the-counter corticosteroid ointments, such as hydrocortisone, may help relieve mild to moderate symptoms if a rash breaks out. Not helpful in relieving the itch are antihistamines such as Benadryl, Zyrtec, Claritin or Clarinex. If the rash is widespread and results in blisters and peeling skin, the person may be susceptible to a secondary infection, especially if the blisters are scratched. The doctor may prescribe an oral corticosteroid (prednisone or similar drugs) for several weeks.

Contrary to popular myth, you cannot acquire poison ivy from burning debris containing the plant or being downwind from it. The oil from the plants causes a problem only when it comes into contact with the skin.

Many other irritating substances that routinely make contact with our skin also can cause a poison-ivy type rash, including nickel, a metal commonly used in costume jewelry. In addition, perfumes, skin lotions and cosmetics may result in contact dermatitis, particularly around the eyes and on the face. The best way to prevent all these skin rashes is to avoid the substances that trigger them.

Dr. Lockey is professor of medicine, pediatrics and public health at USF Health, where he directs the Division of Allergy and Immunology and holds the Joy McCann Culverhouse Chair in Allergy and Immunology.

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