Contact with poison ivy, oak, or sumac can cause a rash (allergic contact dermatitis). The rash is caused by contact with the oil (urushiol) in these plants. Urushiol is an allergen, so the rash is actually an allergic reaction to the oil in these plants.

Normally, the immune system protects the body from viruses and bacteria by producing antibodies to fight them. In an allergic reaction, the immune system overreacts and starts fighting essentially harmless substances as though these substances were trying to attack the body. This overreaction causes problems that affect the skin, nose, lungs, digestive organs, and blood vessels. In the case of contact with poison ivy, oak, or sumac, it results in a rash.

You are not allergic to these plants until contact with urushiol triggers a reaction. The contact with urushiol can either be direct or indirect, such as through clothes, tools, or other objects.

Most poison ivy, oak, and sumac rashes develop within 8 to 48 hours after touching urushiol, but they can take as long as 15 days to form.^{2, 1} The rash usually takes more than a week to show up the first time you get urushiol on your skin. But the rash develops much more quickly (within 1 to 2 days) after later contacts. The rash usually lasts 10 days to 3 weeks, although more severe cases can last up to 6 weeks.¹ After the rash heals, there are usually no permanent scars on the skin.

The rash is not contagious. You cannot catch or spread the rash after it appears, even if you touch it or the blister fluid, because the urushiol will already be absorbed into or washed off the skin. Sometimes people mistakenly believe that the rash is spreading because it appears later on different parts of the body. But the rash only appears where urushiol has come in contact with the skin. So either the rash is still developing from earlier contact or you have touched something that still has urushiol on it.

How sensitive you are to poison ivy, oak, or sumac and the severity of your reaction depend primarily on your age and on the extent of the first contact or first few contacts with the plant. Other influences include physical activity and immune system function.³ Some studies show that how allergic you are to the plants may be inherited.³

Complications

Complications from a poison ivy, oak, or sumac rash usually do not occur in healthy people.

• The rash can occur all over the body (generalized eruption) in highly allergic people.
• Excessive scratching of the rash may discolor the skin or cause a bacterial infection.
• The rash may come back or get worse if treatment ends too soon or if the medicine used is not strong enough.
• In rare cases, kidney problems (nephrotic syndrome) can occur. This can happen in any severe allergic reaction and is not specific to poison ivy, oak, or sumac.