Leaves of three, let them be! You've probably heard that little rhyme about poison ivy. But did you know that poison ivy, poison oak and poison sumac all contain the same rash-causing substance? It's called urushiol, which is a colorless, odorless oil (called resin) contained in the leaves of these plants.

Urushiol can cause an allergic rash in 60 to 80 percent of people who come into contact with it. Mild rashes can be treated at home, and mostly cause discomfort from itching, burning or blistering. Severe, widespread rashes, however, require medical treatment.

Signs and symptoms

Urushiol is considered an allergen because it causes an allergic reaction — which takes the form of a rash, itching and sometimes swelling. Not everyone gets a reaction to urushiol, but about 60 to 80 percent of people do. This reaction can appear within hours of coming into contact with urushiol or as late as five days later.

Typically, the skin becomes red, itchy and swollen and blisters will appear. After a few days, the blisters may become crusty and start to flake off. The rash that people get from poison ivy takes one to two weeks to heal.

What to do

  • Remove any clothing that has touched the plant or rash and wash all recently worn clothing
  • Gently wash skin and scrub under fingernails right away with soap and water
  • Cut fingernails short to keep your child from breaking the skin when scratching
  • Place cool compresses on the skin as needed
  • For itching: add oatmeal to the bath; use calamine lotion (do not use on the face or on the genitals); and, if needed, give your child diphenhydramine


Seek medical care at The Medical Center of Aurora if:

  • The rash covers a large portion of the body or is on the face or genitals
  • The rash is getting worse despite home treatment
  • The skin looks infected (increasing redness, warmth, pain, swelling, or pus)


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Seek emergency medical care if your child:

  • Has a known severe allergy to poison ivy/oak/sumac
  • Develops swelling of the tongue or throat
  • Complains of chest tightness or difficulty breathing
  • Develops widespread redness or swelling
  • Was given a shot of epinephrine (EpiPen)


Think prevention

  • Teach kids what poison ivy/oak/sumac plants look like and how important they are to avoid
  • Make sure kids always wear long-sleeved shirts and pants whenever playing close to these plants
  • Have kids wash their hands well after being outdoors

This content originally appeared on Kidshealth.org.