Poisonous Plants: Poison Ivy, Oak and Sumac

Poison ivy, oak, and sumac are the most common cause of allergic reactions in the United States. Each year 10 to 50 million Americans develop a red, itchy rash after contact with these plants. Poison ivy, oak and sumac grow in every part of the United States except Hawaii, Alaska and some desert areas of Nevada.

Poison Ivy Rash

The allergic rash is caused by contact with an oil called urushiol found in poison ivy, oak, or sumac. Contact can occur in three ways:

  • 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.
  • Airborne particles of urushiol, such as from burning plants, may come in contact with the skin.

The rash is only spread through contact with the oil. You can’t “catch” a rash from someone else or spread it to other parts of the body by touching the blisters or fluid.

After contact, urushiol penetrates the skin in minutes. Usually within 12 to 48 hours, the reaction occurs causing

  • Itching
  • Red streaks or general redness where the plant brushed against the skin.
  • Small bumps or larger raised areas.
  • Blisters that may leak fluid.

The rash may take 10 days or longer to heal.

Sensitivity to Poisonous Plants

We are not born with a sensitivity to poison ivy, oak or sumac and an allergic reaction seldom occurs with the first exposure. Sensitivity only develops after the first direct contact with urushiol and a second encounter may produce a reaction. About 85% of all people will develop an allergic reaction when exposed to these plants; however, sensitivity tends to decrease with age. The rash usually lasts about 10 days to 3 weeks. But it may last up to 6 weeks in more severe cases.

Extreme sensitivity

Some people are very allergic to the oil. In these people, even a little bit of the oil may cause a severe reaction.

Seek immediate medical attention for any of these symptoms:

  • Trouble breathing
  • Extreme swelling on the face (especially the eyelids which may swell shut), mouth, neck, or genitals.
  • Widespread severe rash with blisters. 

Prevention

The best way to prevent poison ivy rashes is to learn to identify these plants and avoid them. 

What poison ivy looks like

  • Each leaf has 3 small leaflets.
  • It grows as a shrub in the far Northern and Western United States, Canada, and around the Great Lakes.
  • It grows as a vine in the East, Midwest, and South.
  • In spring, it has yellow-green flowers.
  • It may have green berries that turn off-white in early fall.

What poison oak looks like

  • Each leaf has 3 small oak-like leaflets.
  • It most often grows as a shrub but can grow as a vine in the Western United States.
  • It may have yellow-white berries. 

What poison sumac looks like

  • Each leaf has a row of paired leaflets and another leaflet at the end with a total of 7 to 13 leaflets per leaf.
  • It grows as a tall shrub or small tree.
  • In the Northeast and Midwest, it grows in standing water in peat bogs.
  • In the Southeast, it grows in swampy areas.
  • It may have yellow-white berries.

Often, the leaves of these plants have spots that look like blotches of black paint. These spots are urushiol, which turns brownish black when exposed to air. In fall, leaves may turn red or yellow while other foliage is still green, and the plants lose their leaves in winter.

Take precautions when you know you will be in areas where these plants are likely to grow:

  • Wear long pants, long sleeves, and closed shoes to help keep the oil from getting on your skin.
  • Wear vinyl or leather gloves.
  • Use a barrier cream or lotion that contains bentoquatam (such as IvyBlock). It can help keep the oil from coming in contact with your skin.
  • Wash well or throw away anything that came into contact with the plants.

Initial Treatment for Rash

If you think you’ve had a brush with poison ivy, poison oak, or poison sumac, take the following steps:

  • Immediately rinse your skin with cold running water. Rinsing the skin within five minute may remove some of the oil and prevent it from spreading to other parts of the body. Rinsing with lukewarm soapy water in the first 30 minutes may also be helpful.
  • Wash your clothing.Thoroughly wash all of the clothes you were wearing when you came into contact with the poisonous plant with a garden hose outside or in a washing machine with detergent. Be careful not to let clothing touch other surfaces in the house.
  • Wash everything that may have the oil on its surface. Besides clothing, the oil from these plants can stick to gardening tools, golf clubs, camping gear and even a pet’s fur. Be sure to rinse your pet’s fur, and wash tools and other gear with warm, soapy water.

Treatment

If you get a mild rash, these tips can help relieve itching.

  • Take cool showers.
  • Apply over-the-counter preparations, such as calamine lotion or Burrow’s solution to the rash.
  • Soak in lukewarm baths with an oatmeal or baking soda solution.
  • Try not to scratch the rash to avoid a skin infection.

In severe cases, prescription cortisone can stop the reaction if used early. Consult your dermatologist if you have been exposed to these plants and developed a severe reaction in the past. Your doctor may prescribe cortisone or other medications to prevent blisters from forming.

Common Myths about Poison Ivy

  • Scratching the blisters will spread the rash. The rash is caused by contact with the urushiol in the plant, not the fluid in blisters. However, scratching may lead to a skin infection.
  • Once allergic, always allergic. A person’s sensitivity changes over time and may decrease with age.
  • Dead plants are not toxic. Dead plants can have active urushiol for several years and should not be handled.
  • Rubbing weeds on the skin can help. Usually prescription cortisone is required to decrease itching.
  • Keeping yourself covered outdoors will protect you. However, urushiol can stick to clothing, which your hands may touch and spread the oil to other parts of the body.