Annual Probability of Poison Ivy Rash

Poison ivy, poison oak, and poison sumac cause more cases of allergic contact dermatitis than all other allergens combined. Approximately 50 million Americans develop a rash from these plants each year, and about 85% of the population is sensitive to urushiol, the oily resin that causes the reaction.

The severity of reaction varies: about 15% of people are essentially immune, about 25% have mild reactions, about 50% have moderate reactions, and about 10% have severe reactions requiring medical attention. Sensitivity can change over a lifetime, with some people becoming more sensitive with repeated exposure.

The rash typically appears 12-72 hours after contact and lasts 1-3 weeks. Treatment includes washing the affected area within 10 minutes of exposure (which can prevent or reduce the rash), calamine lotion, hydrocortisone cream, oral antihistamines, and for severe cases, oral corticosteroids. The oil can remain active on clothing, tools, and pet fur for months to years. Burning poison ivy plants creates aerosolized urushiol that can cause severe lung damage if inhaled.