Poison ivy rash is caused by an allergic reaction to an oily resin called urushiol (u-ROO-she-ol). This oil is in the leaves, stems and roots of poison ivy, poison oak and poison sumac.
Wash your skin right away if you come into contact with this oil, unless you know you’re not sensitive to it. Washing off the oil may reduce your chances of getting a poison ivy rash. If you develop a rash, it can be itchy and last for weeks.
You can treat mild cases of poison ivy rash at home with soothing lotions and cool baths. You may need prescription medication for a rash that’s severe or widespread — especially if it’s on your face or genitals.
- Symptoms
- Signs and symptoms of a poison ivy rash include:
- Redness
- Itching
- Swelling
- Blisters
- Difficulty breathing, if you’ve inhaled smoke from burning poison ivy
Often the rash looks like a straight line 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 spread out. You can also transfer the oil to other parts of your body with your fingers. The reaction usually develops 12 to 48 hours after exposure and lasts two to three weeks.
The severity of the rash depends on the amount of urushiol that gets on your skin. A section of skin with more urushiol on it may develop a rash sooner.
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Your skin must come in direct contact with the plant’s oil to be affected. Blister fluid doesn’t spread the rash.
When to seek medical attention
See your health care provider if:
- The reaction is severe or widespread
- You inhaled the smoke from burning poison ivy and are having difficulty breathing
- Your skin continues to swell
- The rash affects your eyes, mouth or genitals
- Blisters are oozing pus
- You develop a fever greater than 100 F (37.8 C)
- The rash doesn’t get better within a few weeks
This article is written by Mayo Clinic Staff. Find more health and medical information on mayoclinic.org.
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©2020 Mayo Foundation for Medical Education and Research
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