Have you ever walked outside during the height of allergy season and nearly sneezed your head off with a rapid-fire series of "Achoos"? If you're like most, the answer is yes, and while these sneezing fits are both annoying and embarrassing at times, there's a scientific reason for why you sometimes have to sneeze in quick succession.

First, what the heck causes a sneeze in the first place, and what happens inside your body when one sneaks up on you? Well, sneezing is caused by a number of things, from dust and illness, to emotional responses and even sunlight, though the real culprit is the mucus membranes inside your nose and throat. While the exact reason is likely different for every scenario, your mucus membranes are always to blame, because they control the sneeze response.

When a sneeze occurs, "your chest muscles compress your lungs, which send a burst of air upwards," Chanie Kirschner explains for Mother Nature Network. "The throat shuts tight, which then sends the air shooting through your nose at speeds up to 100 mph [160 km/h]." 

Oh, and that 100 mph air is filled with 2,000 to 5,000 droplets of bacteria (gross).

So why do we often do it in threes? While a single sneeze is sometimes enough to clear whatever irritant out of your system, the triple sneeze, according to Live Science's Laura Geggel, happens when we need to get deeper irritants out.

So, the first sneeze likely breaks up the irritant, while the second brings it into the nose, and the third shoots it out. It's a progression needed to clear whatever is causing your mucous membranes to freak out.

If this sounds awfully simple, that's because it is, but the act of sneezing is unique from person to person like our individual laughs are. What causes you to burst out in chuckles is likely different for someone else, which is also true with sneezing, though multiple sneezes are likely all caused when your body is trying harder than normal to clear your airways.

And while we're on the subject, why do people say "bless you" when someone sneezes? According to Jennifer Welsh from Business Insider, the ancient Greeks and Romans used to enjoy sneezing, and thought of them as a sign of good health, which they would celebrate by saying "live long".

This all changed back in the 14th century, when a little thing called the plague was murdering everyone. During this time, Pope Gregory VII asked that people pray post-sneeze to ward off the vicious illness.

So there you have it: our multi-sneezing is basically a three-step process to make sure you expel the potentially dangerous irritants that are trapped in your throat or the back of your nose. If you continue to sneeze, the irritant is likely in the air around you, and you should probably leave for a while until your system calms down.

And if you really can't get enough of sneezes, this disgusting slow-motion footage should sort you out real quick: