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Poison Ivy, Oak, and Sumac (cont.)

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What causes a poison ivy, oak, or sumac rash?

Exposure to all of these plants can produce a rash, which is caused by sensitivity to an oily resin found in these plants called urushiol. This substance can be found on the leaves, stems, flowers, and roots of these plants. Interestingly, it can remain active even after the plant has died. Exposure to even very small amounts of urushiol, amounts less than a grain of table salt, will lead to the development of a rash in 80%-90% of individuals.

The rash (an allergic contact dermatitis) can be caused by direct contact with urushiol by touching the plants or by indirect contact with the plant oil that may have contaminated a pet's fur, tools, clothing, or other surfaces. Airborne contact is also possible if these plants are burned and the urushiol particles land on the skin, and it can affect the lungs as well if the urushiol is inhaled. In the United States, Toxicodendron dermatitis is the most common cause of contact dermatitis.

Sensitivity to urushiol occurs when individuals come into contact with it. The first time a person is exposed, they may not develop a rash. However, with repeated exposure, sensitivity develops that ultimately leads to the development of the characteristic rash. Most people (about 85%) will develop sensitivity, while a small percentage of individuals (about 15%) never develop an allergic reaction to urushiol.

What are risk factors for poison ivy, oak, or sumac rash?

Any individual who comes into contact with these plants is at risk for developing the rash. However, people who spend more time outdoors in geographic areas where these plants are known to grow are at higher risk. This may include certain occupations associated with outdoor work in these areas, such as gardeners, groundskeepers, farmers, forestry workers, and construction workers. Hiking enthusiasts may also be at higher risk if they venture into areas where these plants are present.

Medically Reviewed by a Doctor on 8/1/2016


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