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Diseases and Conditions
Poison ivy rashFrom MayoClinic.com
Special to CNN.com
The advice, "Leaves of three, let them be," is familiar to many people, with good reason. It's a reminder to stay away from plants that feature three leaflets to a stem, such as poison ivy.
Poison ivy and poison oak, another plant with leaflets of three, are common causes of a skin irritation called contact dermatitis. Poison sumac, which has many leaflets to a stem, is another offender. Contact with poison ivy can cause a red, itchy rash consisting of small bumps, blisters or swelling.
Most people are sensitive to poison ivy and these other plants to some degree. The irritating substance is the same for each plant, an oily resin called urushiol (u-ROO she-ol).
Rashes caused by poison ivy and its cousins generally aren't serious, but they certainly can be bothersome. Treatment for poison ivy mostly consists of self-care methods to relieve the itching until the reaction goes away.
Signs and symptoms
Signs and symptoms of a poison ivy rash include:
Often, the rash has a linear appearance because of the way the plant brushes against your skin. But if you come into contact with a piece of clothing or pet fur that has urushiol on it, the rash may be more diffuse.
The reaction usually develops a day or two after exposure and can last up to three weeks, even with treatment. In severe cases, new areas of rash may break out several days or more after initial exposure. This may seem like the rash is spreading. But it's more likely due to renewed contact with the oily resin or to the rate at which your skin absorbed the urushiol.
Your skin must come in direct contact with the oil from the plant in order to be affected. Spreading blister fluid through scratching doesn't spread the rash, but germs under your fingernails may cause a secondary infection.
Poison ivy is a common weed-like plant found across the United States. It may grow as a bush, plant or vine. Poison oak can grow as a low plant or bush, and its leaves resemble oak leaves. The leaves on both poison ivy and poison oak typically grow three leaflets to a stem. Poison sumac may be a bush or a 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.
These plants contain an oily substance called urushiol. When your skin touches the leaves of a poison ivy plant, it may absorb some of the urushiol made by the plant. It takes only a tiny amount of urushiol to cause a reaction, but direct contact is essential.
The resin can spread on your body if you accidentally rub it 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.
You may also develop a reaction indirectly if you touch urushiol left on an item, such as clothing, firewood or even a pet's fur (animals usually aren't affected by urushiol). Burning poison ivy, poison oak or poison sumac can also cause a reaction because the smoke contains the oil.
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.
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.
When to seek medical advice
See your doctor if any of the following occur:
Scratching a poison ivy rash with dirty fingernails may cause a secondary bacterial infection. This might cause pus to start oozing from the blisters. See your doctor if this happens. Treatment for a secondary infection is generally with antibiotics.
Poison ivy rashes typically go away on their own within one to three weeks. In the meantime, you can use self-care methods and over-the-counter medications to relieve signs and symptoms. If the rash is widespread or results in a large number of blisters, your doctor may prescribe a corticosteroid, such as prednisone.
The best way to prevent an allergic reaction is to avoid contact with poison ivy and other poisonous plants. These suggestions may help:
Once a rash has broken out, the following may help to soothe itching and swelling:
May 24, 2006