This is what a sneeze does to your body

1. First of all, something goes up your nose

Your nasal mucosa, the tissue that lines the nasal cavity, recognises an intruder, such as a virus or an allergen, dust, pepper or perfume. It sends a message via the trigeminal nerve (which carries sensation from the face to the brain) to your brain stem. A series of nerve signals then travel to parts of the body (including chest muscles, throat and face) to start the sneeze, explains immunologist Dr Jamie Kiehm.

2. ...Or some other weirdness happens

Inhaling intruders isn’t the only sneeze trigger. In fact, a third of people sneeze when suddenly exposed to bright light – a phenomenon called the photic sneeze reflex, or ACHOO (Autosomal Compelling Helio- Ophthalmic Outburst). Experts believe ACHOO may be caused by sensitivity to stimuli within the part of the brain that processes the eyes’ sensory nerve impulses. Having a full stomach, breathing in cold air and feeling cold are also potential sneeze starters.

3. Then your brain gears up your mouth

The nerve signals from your brain stem direct the soft palate and the uvula to move down a little. The tongue comes up to block the mouth so the majority of what you sneeze out will exit through your nose. Your eyes involuntarily close and your diaphragm thrusts upward simultaneously as your chest muscles contract and push air out of your lungs.

4. That she blows!

Air is expelled through your mouth and nostrils at roughly 160 kilometres an hour. The tongue doesn’t seal off the mouth completely, so some people expel a mixture of snot and spit from there, too (you can thank us for the mental image later). Each sneeze can produce up to 40,000 droplets, which can travel up to three metres.

5. Bless you! and bless you again!

It isn't uncommon to sneeze multiple times – that’s your body working extra hard to get rid of what’s bothering it.

Fast Fact:

Ever notice that you don’t sneeze when you’re sleeping? That’s because the muscles that cause sneezes are atonic, or relaxed, when you’re down for the count.