The sneeze stinks very much. The waste that is present in the sinuses and lungs might lead to the dirty smell of the substance that comes out of the nose in the sneeze. The sneezing smells due to the presence of dead bacteria in it. Almost all the forms of bacteria emit very bad smell mostly. Even during the time of sweating, the dead bacteria smell very much on the skin.
The sneeze stinks due to bad breath. The reason for bad breath is probably because of periodontal disease and tonsillar debris. If the bad stuff or the waste is not sent out for long time from the sinuses and lungs, then the sneezing might smell as the stuff inside might be stinking already. The stinking might occur due to the bacterial infection in the mucus that is to be excreted from the lungs and sinuses.
The stinking of mucus in the sneeze might be due to the problem related to paranasal sinuses. The infection in the sinuses can result in the bad smell of the substance that is expelled when a person sneezes. If the sinuses and the breathing tube do not have any stuff that is retained for long time, sneezing might not stink. If the phlegm is formed since a long time in the lungs, it might stink due to the bacterial growth in it. The persistence of bacterial infection for quite a long duration in the lungs also might cause bad breath along with stinking sneezes.
There is an opinion among some people that not brushing the teeth properly also might cause the sneezing to stink. The sneezing might also stinks when the person is suffering from a disorder like chronic sinusitis. It is observed in some cases that the polyps present in the nostrils gives rise to mucus which stinks. The mucus from polyps stinks even from a certain distance.