Poison Ivy

What causes the rash?

Poison ivy, oak, and sumac are plants which cause an itchy skin rash when directly contacted. The rash is a true allergic response to an oil called urushiol found in the sap of these plants. This oil is a sticky, clear to slightly yellow, and odorless substance which turns dark on exposure to air. Urushiol oils from different plants vary slightly chemically from each other and occasionally individuals can be allergic to one and not the other. The urushiol oil is expelled by an injured plant and can be carried on the surface of objects, clothing, or animals that have come in contact with the toxic sap. These plants can also produce a toxic vapor when burned which can injure the lungs and windpipe (trachea) if inhaled.

Plant Identification

Poison ivy, oak and sumac plants producing urushiol belong to the biological family known as the anacardiaceae family. Most belong to the genus Toxicodendron (T) and several species are know in the United States. For example: T. diversilobumo and toxicarium (poison oak), T. vernix (the poison sumac) and T. radicans (poison ivy). Although these plants like to grow in moist, warm places, their geographic distribution is fairly widespread. They are unknown in Hawaii and northern Alaska. In general, poison oak grows west of the Rockies and poison ivy to the east. Poison ivy and poison oak typically have three leaves per stem, but may have more than three leaves. (So the old adage "leaves three, leave be" is not always correct!) Poison sumac has a longer stem with 7-13 leaves. These plants appear different depending on their location and the season. The toxic sap content is most abundant in spring and summer.

Who is susceptible?

80% of the population will develop a skin rash when contacting the leaves of the poison ivy plant. The severity of the rash varies from person to person. People between 5 and 20 are the most vulnerable to severe forms of skin reaction. Older persons generally have less severe disease. 10% of people develop very severe skin reactions with major swelling and itching.

What does the rash look like?

The ivy oil urushiol penetrates the skin within minutes. First, redness and swelling at the site of contact are visible. Gradually, itching becomes more intense. Blistering of the skin appears within 24- 72 hours (sooner if this is not the first reaction). The typical rash is arranged as a red line on an exposed area of the body caused by the plant dragging across the skin. However, patches of skin rash can break out on the neck or between the fingers. The rash will continue for up to two weeks. If the skin is broken by scratching, infection of the skin can complicate the condition.