Poison ivy occurs when a person comes into contact with the leaf and/or internal parts of the stem or root. The rash typically develops within 24 to 48 hours of exposure, though it can develop sooner. It usually appears in a linear or circular pattern with itchy red blotches. Rhus dermatitis is incredibly itchy, to the point that the victim may scratch the skin to the point of bleeding.
The resin itself can be active for years following exposure (meaning that it can be spread to others who come into contact with the clothing of an affected individual). By contrast, the fluid from the blisters cannot spread the rash.
If untreated, the rash usually heals in around three weeks.