Which two systems cause you to sneeze when smelling pepper?

The two systems involved in sneezing when smelling pepper are the olfactory system and the trigeminal system. The olfactory system detects the scent of pepper, while the trigeminal system responds to irritants in the nasal passages, triggering a sneeze as a reflex to expel the irritant. This reaction is often heightened by the strong volatile compounds found in pepper, which can irritate the nasal mucosa.