The reaction caused by poison ivy, urushiol-induced contact dermatitis, is an allergic reaction. For this reason some people claim to be "immune" to its "poisonous" effects. However, sensitivity can develop over time. For those who are affected by it, it causes a very irritating rash. If poison ivy is burned and the smoke then inhaled, this rash will appear on the lining of the lungs, causing extreme pain and possibly fatal respiratory difficulty. If poison ivy is eaten, the digestive tract and airways will be affected, in some cases causing death.
Huh.