What are the stages of poison ivy?

Bad to worse: Most people develop allergic contact dermatitis to the waxy oil of urushiol that makes up much of the plant resin. It is a delayed-type hypersensitivity that can vary somewhat based on the type/degree of exposure and how allergic the patient is. Over time, lesions can go from dry and red, to bumpy, to huge water blisters (bullae) before they crust over and clear up. The lesions are not contagious.