What are poison ivy, oak, and sumac?
Poison ivy, oak, and sumac are plants that can cause a red, itchy rash called allergic contact dermatitis. It is the most common skin problem caused by contact with plants.
What causes the rash?
The rash is caused by contact with a sticky oil called urushiol (say "yoo-ROO-shee-all") found in poison ivy, oak, or sumac. You can get the rash from:
- Touching or brushing against any part of these plants, including the leaves, stems, flowers, berries, and roots, even if the plant is dead.
- Touching anything that has come in contact with these plants, such as clothing, sporting gear, gardening tools, or pet fur.
- Exposure to smoke. Urushiol from burning poison ivy, oak, or sumac attaches to smoke particles and can cause a rash on any part of the body.
The rash is only spread through the oil. You can't catch a rash from someone else by touching the blister fluid.
The rash is an allergic reaction to the oil. You become allergic to it through contact. After you have come in contact with these plants, your immune system may start to react to the oil as though it's a harmful substance.
What are the symptoms?
The usual symptoms of the rash are:
- Red streaks or general redness where the plant brushed against the skin.
- Small bumps or larger raised areas (hives).
- Blisters that may leak fluid.
Some people are very allergic to the oil. In these people, even a little bit of the oil may cause serious symptoms that need medical attention right away, such as:
- Trouble breathing.
- Swelling of the face, mouth, neck, or genitals. The eyelids may swell shut.
- Widespread, large blisters that ooze a lot of fluid.
The rash usually takes more than a week to show up the first time you have a reaction to the oil. It develops in a day or two on later contacts. The rash may form in new areas over several days, but you will only get a rash where the oil touched your skin.
The rash usually lasts about 10 days to 3 weeks. But it may last up to 6 weeks in more severe cases.
How is the rash diagnosed?
A doctor can usually diagnose the rash by looking at it and asking questions about:
- When you were exposed to the plant.
- How long it took the rash to develop.
- Other rashes you have had.
- Your outdoor activities, work, and hobbies.
How is a poison ivy, oak, or sumac rash treated?
Mild to moderate rash
If you get a mild rash, you can take care of it at home. Here are some tips to help with itching:
- Apply a cool, wet cloth for 15 to 30 minutes several times a day.
- Take short, cool baths.
- Use calamine lotion to help relieve itching.
- Try not to scratch the rash. Scratching could cause a skin infection.
If you have trouble sleeping because of the itching, taking diphenhydramine (Benadryl) may help.
See your doctor if:
- The rash covers a large area of your body.
- Your symptoms are severe.
Your doctor may treat your rash with prescription corticosteroid pills, creams, or shots.
How can you prevent the rash?
If you think you have touched any of these plants:
- Wash your skin right away with plenty of water and mild soap (such as dishwashing soap) or rubbing alcohol. Rinse often, so that the soap or rubbing alcohol doesn't dry on the skin and make the rash worse.
- Use a brush to clean under your nails.
- Wash any clothing or other items that might have the oil on them. Do it right away.
The best way to prevent future rashes is to learn to identify these plants and avoid them.
When you can't avoid contact with the plants:
- Wear long pants, long sleeves, and closed shoes to help keep the oil from getting on your skin.
- Wear vinyl or leather gloves. Rubber (latex), cotton, or wool gloves offer no protection.
Experts say not to burn plants like poison ivy, oak, or sumac. When these plants burn, urushiol attaches to smoke particles. Exposure to the smoke can cause a rash on your skin. Breathing in the smoke can also hurt your lungs.
Current as of:
March 3, 2021
Author: Healthwise Staff
William H. Blahd Jr. MD, FACEP - Emergency Medicine
Adam Husney MD - Family Medicine
E. Gregory Thompson MD - Internal Medicine
Martin J. Gabica MD - Family Medicine
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