The leaves of both of these plants are deciduous and change color in the fall. Allergic reactions differ among individuals.
The toxic substance that causes rashes is an oil within the plant called urushiol.  It oozes from areas of the plant that have been cut,
abraded, or eaten at by insects.  The oil may persist for five years even after the plant dies.  Rashes do not spread by scratching unless
there is residual oil on the skin, nor do they spread from blister rupture.  Reaction may not occur immediately after contact.
Avoidance of the plant is recommended, even for those persons who are not hypersensitive.
Ironically, the oil would be harmless were it not for the overreaction of the body's immune system.
Wash with soap and water and wipe with isopropyl alcohol.  Jewelweed also works well as a natural remedy.