Return to Previous Page

Easing the Itch of the Great Outdoors

How to Prevent and Treat Allergic Reactions to Poison Plants

Allergy image

Many native and exotic plants are poisonous to humans when ingested or if there is skin contact with plant chemicals. However, the most common problems with poisonous plants arise from contact with the sap oil of several ever-present native plants that can cause an allergic skin reaction – poison ivy, poison oak, and poison sumac.

Poison ivy, oak, and sumac release an oil called urushiol when the leaf or other plant parts are bruised, damaged, or burned. When the oil gets on the skin, an allergic reaction (called contact dermatitis) occurs in most exposed people, creating an itchy, red rash with bumps or blisters.

One or more of the most common poisonous plant species are found throughout the United States (except Alaska and Hawaii). These plants can be found in forests, fields, wetlands, and along streams, roadsides, and even in urban environments, such as parks and backyards. Poison ivy can be found across the United States, except California, Alaska, and Hawaii. Poison oak grows primarily in the Southeast and along the west coast. Poison sumac is abundant along the Mississippi River and boggy areas of the Southeast.

The old saying “Leaves of three, let it be” is a helpful reminder for identifying poison ivy and oak, but not poison sumac, which usually has clusters of seven to thirteen leaves. Even poison ivy and poison oak may have more than three leaves, and their form may vary greatly depending upon the exact species encountered, the local environment, and the season. Being able to identify local varieties of these poisonous plants throughout the seasons and differentiating them from common nonpoisonous look-a-likes are the major keys to avoiding exposure.

These plants can be found in forests, fields, wetlands, and along streams, roadsides, and even in urban environments.

Eastern poison ivy is typically a hairy, ropelike vine with three shiny, green (or red in the fall) leaves budding from one small stem. Western poison ivy is typically a low shrub with three leaves that does not form a climbing vine. Both may have yellow or green flowers and white to green-yellow or amber berries.

Poison oak typically grows as a shrub with leaves of three, similar to poison ivy, but Pacific poison oak may be vinelike. Poison oak also may have yellow or green flowers and clusters of greenyellow or white berries.

Poison sumac is a woody shrub that has stems that contain seven to thirteen leaves arranged in pairs. It may have glossy, pale yellow or creamcolored berries.

People may become exposed to urushiol through direct contact with the plant; indirect contact, such as touching tools, animals, or clothing that have urushiol on them; or inhalation of particles containing urushiol from burning plants. Signs or symptoms associated with dermal contact with poisonous plants may include a red rash within a few days of contact; possible bumps, patches, streaking, or weeping blisters (blister fluids are not contagious); swelling; and itching.

You can prevent contact with poisonous plants by taking these steps:

  • Wear long sleeves, long pants, boots, and gloves when outdoors, especially in wooded areas. Wash exposed clothing separately in hot water with detergent.
  • Barrier skin creams, such as a lotion containing bentoquatam, may offer some protection before contact. Barrier creams should be washed off and reapplied twice a day.
  • After use, clean objects exposed to poison plants with rubbing alcohol or soap and lots of water. Urushiol can remain active on the surface of objects for up to five years. Wear disposable gloves during this process.
  • Do not burn plants that may be poison ivy, oak, or sumac. Inhaling smoke from burning poisonous plants can cause severe allergic respiratory problems.

People who have been exposed to poisonous plants should follow these steps:

  • Immediately rinse skin with rubbing alcohol, specialized poison plant washes, degreasing soap (such as dishwashing soap) or detergent, and lots of water. Rinse frequently so that wash solutions do not dry on the skin and further spread the urushiol.
  • Scrub under nails with a brush.
  • Apply wet compresses, calamine lotion, or hydrocortisone cream to the skin to reduce itching and blistering. Follow the directions on any creams and lotions. Do not apply to broken skin, such as open blisters. Oatmeal baths may also relieve itching.
  • An antihistamine, such as Benadryl, can be taken to help relieve itching. vIn severe cases or if the rash is on the face or genitals, seek professional medical attention.
  • Call 911 or go to a hospital emergency room if you have a severe allergic reaction, such as swelling or difficulty breathing, or have had a severe reaction in the past.

Source: U.S. Centers for Disease Control and Prevention,

This article was originally published in Coping® with Allergies & Asthma magazine, Spring/Summer 2010.