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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 an extremely 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. Some leaves have smooth edges, while others have a jagged, tooth-like appearance. 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 oak may have yellow-white berries.
- 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 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. Even a small amount of urushiol can cause a reaction. Urushiol is very sticky and doesn't dry, so it easily attaches to your skin, clothing, tools, equipment or pet's fur.
You can get a poison ivy reaction from:
- Direct touch. If you directly touch the leaves, stem, roots or berries of the plant, shrub or vine, you may have a reaction.
- Urushiol remaining on your skin. You may develop a poison ivy rash after unknowingly rubbing 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.
- Urushiol on objects. If you touch urushiol left on an item, such as clothing or firewood, you may have a reaction. Although animals usually aren't affected by urushiol, if it's on your pet's fur and you touch your pet, you may develop a poison ivy rash. 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.
- Inhaling smoke from burning poison ivy, oak or sumac plants. 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 that's still on that person or on his or her clothing.
- Contact dermatitis and patch testing. In: Habif TP. Clinical Dermatology. 5th ed. Maryland Heights, Mo.: Mosby, Inc.; 2010. http://www.mdconsult.com/book/player/book.do?method=display&type=bookPage&decorator=header&eid=4-u1.0-B978-0-7234-3541-9..00013-4--s0105&displayedEid=4-u1.0-B978-0-7234-3541-9..00013-4--s0115&uniq=186228941&isbn=978-0-7234-3541-9. Accessed Feb. 28, 2010.
- Contact dermatitis: A practice parameter. Palatine, Ill.: Joint Council of Allergy, Asthma and Immunology. http://www.aaaai.org/professionals/resources/pdf/contact_dermatitis_%202006.pdf. Accessed Feb. 28, 2010.
- Contact dermatitis. The Merck Manuals: The Merck Manual for Healthcare Professionals. http://www.merck.com/mmpe/print/sec10/ch114/ch114c.html. Accessed Feb. 25, 2010.
- Outsmarting poison ivy and other poisonous plants. U.S. Food and Drug Administration. http://www.fda.gov/forconsumers/consumerupdates/ucm049342.htm. Accessed Feb. 28, 2010.
- Poison ivy, oak and sumac. American Academy of Dermatology. http://www.aad.org/public/publications/pamphlets/skin_poison.html. Accessed Feb. 25, 2010.
- Gladman AC. Toxicodendron dermatitis: Poison ivy, oak, and sumac. Wilderness and Environmental Medicine. 2006;17:120.
- Bovine cartilage. Natural Medicines Comprehensive Database. http://www.naturaldatabase.com. Accessed Feb. 28, 2010.
- Poison ivy, oak and sumac. PDRHealth (Physician's Desk Reference). http://www.pdrhealth.com/disease/disease-mono.aspx?contentFileName=BHG01DE21.xml&contentName=Poison+Ivy%2c+Oak%2c+and+Sumac&contentId=120&TypeId=1. Accessed Feb. 28, 2010.
- Mark BJ. Allergic contact dermatitis. Medical Clinics of North America. 2006;90:169.
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