Skin Problems & Treatments Health Center

Poison Ivy, Oak, and Sumac -- the Basics

Poison ivy, poison oak, and poison sumac are all plants that can cause a temporary, irritating rash when they come in contact with your skin. This rash is a form of allergic contact dermatitis. Dermatitis simply means an irritation of the skin. It's called "allergic contact dermatitis" because the rash is caused by contact with a substance you're allergic to.

Who Is Allergic to Poison Ivy, Poison Oak, and Poison Sumac?

Have you ever wondered: Do I have poison ivy? What you're really asking is: Am I allergic to the plant?Not everyone is. About 85% of Americans are allergic to poison ivy, leaving about 15% resistant to any reaction.

If you are allergic to poison ivy, you're more likely to be allergic to poison oak and poison sumac as well because all three plants contain the same rash-triggering plant oil called urushiol. You're also more likely to have an allergic reaction to other plant resins, such as the oil from Japanese lacquer trees (used on furniture), mango rinds, and cashew shells.

Sensitivity to poison ivy, poison oak, and poison sumac varies from a mild to severe reaction, and may not cause any reaction at all the first time you're exposed. Some adults who reacted to poison ivy as a child may find that they are now less sensitive. Some may even lose their sensitivity altogether.

What Causes the Rashes of Poison Ivy, Oak, and Sumac?

With poison ivy, poison oak, and poison sumac, the sap in the leaves, stems, and roots of these plants contain an oil called urushiol (pronounced yoo-ROO-shee-all).Many people have an allergic reaction when urushiol touches the skin, which produces the rash. You may be caught by surprise, thinking you haven't touched any of these poisonous plants -- thinking only of the leaves -- but you may have unwittingly come in contact with their roots or stems. 

Urushiol quickly penetrates the skin, often leaving red lines that show where you brushed against the plant. From 12 to 72 hours later, symptoms appear. Scratching the itchy rash doesn't cause it to spread, but can prolong skin healing and cause a secondary infection. The rash isn't contagious, so you won't spread it to others by going to school or work. 

Three types of transmission can occur:

• Direct contact, when you touch or brush your skin directly against the plant.
• Indirect contact when you touch pets, gardening tools, sports equipment, or other objects that had direct contact with the plant.
• Airborne contact from burning these plants, which releases particles of urushiol into the air that can penetrate your skin, eyes, nose, throat, or respiratory system.

What Are the Symptoms of an Allergic Reaction to These Plants?

Symptoms, which generally last from one to two weeks, include: 

• Red streaks or patches
• Itching
• Rash
• Swelling
• Blisters that may "weep" (leak fluid) and later crust over
• Inflammation and a burning sensation

Does it matter which plant you're exposed to? Poison ivy, oak, and sumac all fall into the plant species called Toxicodendron, so the allergic reaction to all of these plants has the same name: Toxicodendron dermatitis. There are actually four poisonous plants in this group, since poison oak has both a western and an eastern variation. All four plants contain urushiol, so the skin reaction and treatment is essentially the same.