The Science of Sneezing

Along with coughing and vomiting, sneezing is one of the body's top tools for getting rid of germs. One sneeze leaves the body at about 100 mph (161 kph), carrying as many as 100,000 pathogens with it. That's quite a feat, and pulling it off is a physiological act of coordination and timing.

The Basics of Breathing

Your ability to sneeze builds off of your body's natural breathing patterns. When you inhale, your diaphragm, a sheet of muscle below your ribs, moves downward. This lowers the pressure within your chest cavity, and your lungs expand to fill it, pulling air in from outside as they go. Your diaphragm doesn't do this job alone, though. Muscles called external intercostals contract, pulling each rib toward the one above it. The ribs swing up and out, increasing the space within the chest even more. Muscles in the neck and upper chest pull the collarbone and upper ribs upward, expanding the top of the chest cavity.

In a normal exhale, everything simply relaxes. The chest cavity and the lungs naturally return to their original, unstretched positions, and air moves out of lungs through the nose or mouth. But in a more forceful exhale, such as when you're exercising, muscles called the internal intercostals contract, pulling each rib downward toward the one below it. The ribs swing down and in, making the space in the chest cavity smaller. Muscles in the abdomen contract as well, pushing the belly in and the diaphragm up.

From a Breath to a Sneeze

A sneeze is a basic breath taken to an extreme. First, the diaphragm, external intercostals and other muscles all contract, causing the lungs to expand quickly and air to rush in to fill them. Then, just as quickly, the abdominal muscles, internal intercostals and other muscles in the body contract, forcing the air back out again. But that's only part of the anatomical story. The palate -- the roof of the mouth -- also shifts, allowing air to move out of the mouth and nose simultaneously.

So how does the body know when it's time to sneeze? Nerve endings in the nose detect irritation, which can be the result of anything from wayward pollen particles to viral activity. The nerves carry impulses to a region of the brain stem known as the sneeze center. The sneeze center sends instructions to all the parts of the body involved in the sneeze, coordinating their responses with a high degree of precision.

The Downside of Efficiency

A sneeze's basic goal is to move irritants, allergens and pathogens out of your body quickly, so they can't harm you. Unfortunately, all that power comes with a price -- one person's sneezes can make other people sick.

The best defense: blocking that 100-mph wind of fluid and germs. Sneeze into a tissue and throw it away, or sneeze into the crook of your elbow. Either way, you won't wind up with a handful of germs to spread around – and that’s nothing to sneeze about.