The old wives’ tale warns us that if you hold in a sneeze, your head might explode. That won’t happen, but you can do yourself some harm.
A sneeze is a very complicated thing that involves many areas of the brain. A sneeze is a reflex triggered by sensory stimulation of the membranes in the nose, resulting in a coordinated and forceful expulsion of air through the mouth and nose. The Guinness Book of World Records reports the longest sneezing bout ever recorded was that of a schoolgirl from the United Kingdom. She started sneezing on January 13, 1981, and didn’t stop sneezing for 978 days.

The air expelled by sneezes is said to travel up to one hundred miles per hour, and an unimpeded sneeze sends two to five thousand bacteria-filled droplets into the air. Holding in a sneeze potentially can cause fractures in the nasal cartilage, nosebleeds, burst eardrums, hearing loss, vertigo, detached retinas, or temporary swelling called facial emphysema. Therefore it is best to let your sneeze fly, but please cover your nose and mouth.

Source: “Why do men have nipples” By William Goldberg, M.D., and Mark Leyner