Poison ivy rash

Poison ivy rash is caused by a sensitivity to an oily resin called urushiol (u-ROO-she-ol), which is found in the leaves, stems and roots of poison ivy, poison oak and poison sumac.

At least 50 percent of the people who come into contact with these plants develop an itchy rash. The most dangerous type of exposure occurs when the plant is burned and the smoke is inhaled, which can affect your lungs.

Mild cases of poison ivy rash require no medical treatment. For more severe or widespread rashes — especially if it's on your face or genitals — your doctor may suggest taking corticosteroid pills, such as prednisone, for a few weeks.

Symptoms Causes Risk factors Complications Prevention

Signs and symptoms of a poison ivy rash include:

  • Redness
  • Itching
  • Swelling
  • Blisters

Often, the rash looks like a straight line because of the way the plant brushes against the 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. The reaction usually develops 12 to 48 hours after exposure and typically lasts two or 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. You can also transfer the oil to other parts of your body with your fingers.

Your skin must come in direct contact with the plant's oil to be affected. Blister fluid doesn't spread the rash.

When to see a doctor

See your doctor if:

  • The reaction is severe or widespread
  • The rash affects your face 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

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