There are several causes: 1. Allergic rhinitis, some of them will sneeze incessantly, mainly because of itchy nasal cavity, frequent sneezing and clear water-like nasal discharge, mainly because of exposure to pollen, dust, dust mites, or seasonal allergic rhinitis attacks, most of which can be triggered by colds. 2. Influenza, some influenza has upper respiratory symptoms, manifested as runny nose, sneezing, nasal congestion and cough. 3, some acute infectious diseases, some accompanied by symptoms of upper respiratory tract infection, some will also have a runny nose, common are measles, polio, viral encephalitis, will have sneezing phenomenon. Some other smells have irritating odors, such as smelling an irritating scent or odor, and some will also stimulate sneezing.