Hold that sneeze? Not likely, Louise

Of all the involuntary actions carried out by the human body, nothing rivals the sneeze.

A sneeze occurs in three stages. First, your head moves up and back as you take a sudden breath. (This is the “ah” part of the sneeze.) Second, you pause for a moment after your lungs fill with air. Third, your head moves forward and down as you contract the muscles in your chest, throat and abdomen. (This is the “choo” part of the sneeze.)

In the process, you expel air and tiny droplets out of your nose and mouth at 100 mph - faster than a cheetah chasing down a gazelle on the African savanna.

The nose and sinus cavities are lined with small hairs, mucus-producing glands and hairlike microscopic structures called cilia. Hairs and nasal mucus trap dust, mold and germs. Cilia beat slowly to move foreign matter to your throat, where it can be swallowed. The acid in your stomach destroys most of the viruses and bacteria you swallow throughout the day.

But some invaders irritate the nerves associated with these structures. Besides colds and allergies, common triggers include smoke, strong smells and animal dander (sloughedoff skin cells). Less common triggers include plucking an eyebrow, hard exercise, and some people sneeze when exposed to bright light.

When something “tickles” or irritates the nerves in your nasal passages, nerves zap a signal to the sneeze center in your lower brain stem, the medulla, which conducts involuntary activities. Your brain responds by orchestrating all of the muscular actions required.

Eye muscles aren’t needed, but you may have noticed that it’s impossible to sneeze without closing your eyes. Another odd fact: People don’t sneeze while asleep.

You should cover your nose and mouth when you sneeze because an unchecked sneeze will spread thousands of germs.

The worst sneeze is the one that can’t decide if it needs to come out or not. I don’t know why this happens, but when it does, you get stuck between the “ah” and the “choo.” It’s like “sneeze limbo,” but eventually the feeling goes away.