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Causes
By Mayo Clinic staff
Poison ivy, poison oak and poison sumac can all cause contact dermatitis and the resulting itchy rash.
- Poison ivy is a common weed-like plant that may grow as a bush, plant or thick, tree climbing vine. The leaves typically grow three leaflets to a stem. The leaves vary greatly in their shape, color and texture. Some leaves are shiny, smooth and elliptical. Others are elongated and toothed with distinct leaflets. In the fall, the leaves may turn yellow, orange or red. Poison ivy can produce small, greenish flowers and green or off-white berries.
- Poison oak can grow as a low plant or bush, and its leaves resemble oak leaves. Like poison ivy, poison oak typically grows three leaflets to a stem.
- Poison sumac may be a bush or a small tree. It has two rows of leaflets on each stem and a leaflet at the tip. The smooth edges of its leaves distinguish it from its harmless sumac relatives.
The irritating substance is the same for each plant, an oily resin called urushiol. When your skin touches the leaves of the plant, it may absorb some of the urushiol made by the plant. It takes only a tiny amount of urushiol to cause a reaction. Urushiol is very sticky and doesn't dry, so it easily attaches to your skin, clothing, tools, equipment or your pet's fur.
You can get a poison ivy reaction if you:
- Directly touch the leaves, stem, roots or berries of the plant, shrub or vine.
- Unknowingly rub the urushiol onto other areas of your skin. For example, if you walk through some poison ivy then later touch your shoes, you may get some urushiol on your hands, which you may then transfer to your face by touching or rubbing.
- Touch urushiol left on an item, such as clothing, firewood or even a pet's fur (animals usually aren't affected by urushiol). Urushiol can remain allergenic for years, especially if kept in a dry environment. So if you put away a contaminated jacket without washing it and take it out a year later, the oil on the jacket may still cause a reaction.
- Burn the plants and inhale the smoke. Even the smoke from burned poison ivy, poison oak and poison sumac contains the oil and can irritate or injure your eyes or nasal passages.
A poison ivy rash itself isn't contagious. Blister fluid doesn't contain urushiol and won't spread the rash. In addition, you can't get poison ivy from another person unless you've had contact with urushiol on that person.
