Humans do not sneeze in their sleep. This is because when the human body is asleep, it enters a state of rapid eye movement (REM) atonia, during which the muscles do not move, and the motor neurons are not stimulated. Sneezes result from stimulation of the motor neurons, so when a body is in REM atonia, it cannot sneeze. If there is enough of a stimulus, however, the body will wake up to sneeze.
More facts about sneezing:
- A sneeze can send more than 100,000 germs into the air.
- Although most sneezes are caused by stimulation of the neurons in the nose's mucous membranes, some people also can be made to sneeze by sudden exposure to bright light — this is called a photic sneeze — or even by a very full stomach, which is called snatiation, or a gastric sneeze.
- The animal that sneezes the most is the iguana. Iguanas also are the most productive sneezers, and they sneeze to expel salt from their bodies.