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Poison ivy, poison oak, and poison sumac contain an irritating, oily sap. The sap contains a chemical (urushiol) that triggers an allergic reaction when it comes into contact with the skin, resulting in an itchy rash that can appear within hours of exposure, or three to five days later. A person can be exposed to urushiol directly or by touching objects (such as gardening tools, camping equipment and even a pet’s fur) that have come into contact with the sap of one of the poison plants.
All three plants contain the same irritating substance and cause the same reaction, which generally occurs in phases:
Redness and itching of the skin are the first signs of exposure
Rash erupts on the skin, often in a pattern of streaks or patches where the plant has come into contact with the skin
Rash develops into red bumps (called papules) or large, oozing blisters
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Poison ivy, poison oak, and poison sumac are three of the most common causes of allergic contact dermatitis in North America. Some experts estimate that three out of four people are sensitive to these plants, although the degree of sensitivity varies. Cases of poison plant allergy occur most frequently during the spring, summer and early fall, when people spend more time outdoors.
An allergic reaction to a poison plant is diagnosed based on review of recent activities, the typical pattern of symptoms, and the appearance of the rash. Most rashes caused by poison ivy, poison oak, or poison sumac are mild and last from 5 to 12 days. In severe cases, the rash can last for 30 days or longer.
Contrary to popular belief, the rash itself does not "spread" like an infection. It is the unknowing transfer of the oil to other parts of the body by touching that gives the spreading affect. Once the oil is completely removed from skin and clothing, no further rash will result. Some rashes will appear sooner than others depending on the sensitivity of the skin area and the degree of contact. It can take longer for the rash to appear on certain areas of the body, especially areas such as the soles of the feet where the skin is thicker. This may give the appearance that the rash has spread from one part of the body to another. You also can be re-exposed to the irritating substance in poison plant by touching gardening tools, sports equipment, or other items that were not cleaned after being in contact with the plants. Scratching or touching the rash and fluid from blisters will not cause the rash to spread because irritant is not present in the blister fluid.
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You can take steps to prevent exposure:
Learn to identify poison ivy, poison oak and poison sumac, and avoid contact with them.
Remove these plants from around your home, especially in areas where you may be working or playing. Wear protective clothing that can be discarded or washed immediately after spraying or pulling poison plants.
When walking in the woods or working in areas where these plants may grow, cover your skin as much as possible by wearing long pants, long-sleeves, shoes and socks.
Do not let pets run in wooded areas where they may be exposed to the poison plants. They can carry the irritating substance contained in these plants back home on their fur.
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An allergic reaction to a poison plant cannot be cured, but the symptoms can be treated. You may take cool showers and apply an over-the-counter lotion or cream such as calamine or hydrocortisone to help relieve the itch. If your reaction is severe or involves mucous membranes, you may require a prescription medication for relief. Immunotherapy is not available for allergies to poison ivy, poison oak, and poison sumac.
If you think you may have been exposed to one of the poison plants:
Remove your clothes.
Wash all exposed areas with cool running water. Use soap and water if you can. Be sure to clean under your fingernails. In the woods, the water of a running stream can be an effective cleanser.
Wash your clothing and all gardening tools, camping gear, sports equipment, and other objects that were in contact with the plants.
Bathe pets exposed to the plants.
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