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What Are Poison Ivy, Poison Oak, and Poison Sumac?

Poison ivy, poison oak and poison sumac cause a short-lived but extremely irritating allergic form of contact dermatitis. The rash generally develops within two days, peaks after five days, and starts to decline after about a week or 10 days. While some people survive exposure without ill effects, complete immunity is unlikely; people who seem immune at one time and place may find themselves vulnerable in other situations.

What Causes Them?

The leaves, stems and roots of poison ivy, oak and sumac plants contain the resin urushiol, and even small amounts on exposed skin can trigger an inflammatory allergic reaction.

Urushiol can be transferred by fingers or animal fur and can remain on clothing, shoes and tools for a number of months. Urushiol particles can also travel in the wind when the plant is burned in a fire. Scratching the rash does not spread the poison to other parts of the body, but it can prolong the discomfort and cause a secondary infection.