Here are the reasons why they sneeze at odd times, and why all of us sneeze in the first place.

Stouffer, 30, isn't the only one with a fickle nose. Many people sneeze at peculiar moments -- such as after exercise , plucking their eyebrows, in the sunshine, or after sex .

Larissa Stouffer of Melrose, Mass., usually sneezes not once, not twice, but three times. She sneezes as she gets into a car if it's sunny outside, but not when it's cloudy; her dad does the same thing. And as soon as she pops some mint chewing gum into her mouth, out comes an achoo.

11 Surprising Sneezing Facts

1. "Sneezes start in your nerves," says Neil Kao, MD, an allergy and asthma specialist at the Allergic Disease and Asthma Center in Greenville, S.C.

Everyone's nervous system is basically wired in the same way, Kao explains. But signals traveling along nerves can take slightly different paths to and from the brain, resulting in different sneeze scenarios from person to person.

"It's a nerve transmission that tells your brain something is in your nose that needs to come out," Kao tells WebMD.

2. Sneezing helps keep your body safe. "Sneezing is an important part of the immune process, helping to keep us healthy and sniffle-free" Kao says.

Sneezes protect your body by clearing the nose of bacteria and viruses, Kao explains. When something enters your nose or you encounter a trigger that sets off your "sneeze center" in your brain, located in the lower brain stem, signals are rapidly sent to tightly close your throat, eyes, and mouth. Next, your chest muscles vigorously contract, and then your throat muscles quickly relax. As result, air -- along with saliva and mucus -- is forced out of your mouth and nose. Voila, you've sneezed.

3. Sneezes are speedy. "Sneezes travel at about 100 miles per hour," says Patti Wood, author of Success Signals: Understanding Body Language . She adds that a single sneeze can send 100,000 germs into the air.

4. Plucking your eyebrows may make you sneeze. Plucking may set off a nerve in your face that supplies your nasal passages. As a result, you sneeze.