Colds and flu

06 May 2016

Why you can’t keep your eyes open while sneezing

A sneeze is an involuntary, forceful expulsion of air through the mouth and nose. When we have a cold or flu, a sneeze can spread rhinoviruses and make other people around us sick too.

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With winter on our doorstep, we all know the symptoms of colds, stuffy nose, coughing, sore throat, headache and generally feeling lousy. Highly contagious rhinoviruses cause most colds, says Dr Marvin Hsiao, medical virologist at the University of Cape Town’s Department of Clinical Laboratory Sciences.

Flu shows no mercy

He explains that the viruses that cause these infections of the upper airways are mostly spread via direct contact with tiny air droplets. Fortunately, colds are usually short-lived.

“Cold symptoms develops gradually and may make you feel unwell for a few days, but are far milder than influenza (flu), which is caused by very different virus types A, B and C,” Dr Hsiao comments.

Read: How far does a sneeze really travel?

Flu whacks you suddenly and shows no mercy. In fact, flu symptoms like high fever, chills, fatigue and aching muscles can make you feel like death for up to a few weeks.

With sneezing being a common cold symptom, ever wondered why you sneeze, what stops you from keeping your eyes open when you sneeze and whether your eyes will pop out if you do?

There is no single answer to why we sneeze (known medically as sternutation). Sneezing is a semi-autonomous reflex mechanism, similar to the one your body uses to yank your hand away from a hot stove, says immunology expert Dr Brian Smart, chairman of the US-based Asthma and Allergy Centre of the DuPage Medical Group. Yet even scientists admit the actual reflex is generally not that clear-cut.

Some people sneeze when exposed to cold air or bright light. It seems your body uses sneezing to clear the nasal cavity and expel physical irritants (e.g. pollution or smoke) and environmental particles like dust, mildew, mould, pollen and pet hair.

Read: Flu and colds: are you still contagious?

When you have a cold or flu, the inside of the nasal cavity becomes swollen and more sensitive than usual, so the slightest irritation will trigger sneezing, explains Dr Smart.

For a millisecond your eyelid muscles lock

A sneeze starts when tiny nerve endings "detect an irritant in your nose, like dust, dirt, bacteria or other particles trapped in nasal mucus", says the National Institute of Allergy and Infectious Diseases (NIH).

It explains on the NIH website that these nerves then send a signal to your brain's sneeze centre called the medulla, which sends messages to other parts of the body.

This triggers the muscles in your chest and abdomen to compress your lungs and produce a blast of air. At the same time, the back of your tongue lifts up, partially closing the passage to your mouth and forcefully pushing air out through your nose and mouth.

For a millisecond your eyelid muscles lock, squeezing your eyes shut as you sneeze, despite your attempt to keep them open.  

Is there any truth that your eyes will pop out if you sneeze too forcefully? Highly unlikely, says Dr Smart. So don’t worry about your eyeballs rolling around on the floor next time you sneeze.

Read: How does flu spread?

Rest assured your eyes are firmly attached to your head by several muscles, the same ones you use to roll your eyes or sneak a peek at someone out of the corner of your eye.   

Sneezing for science

Turns out, the science of sneezing fascinates medical researchers, who even measure weird and slightly gross things like the speed of a sneeze. A single sneeze can spread between 2,000 and 5,000 droplets of mucus and air over a distance of 45.7metres at an astounding speed of more than 160km per hour!  

Researchers from the Massachusetts Institute of Technology (MIT) released new high-speed videos in 2016. They show that when people sneeze, they produce a complex fluid cascade, not just a simple uniform spray of droplets, as previously thought.

“When someone sneezes, they launch a sheet of fluid that balloons before it breaks apart in long filaments.

"These destabilise and finally disperse as a droplet spray, almost like flinging paint through the air,” explains Professor Lydia Bourouiba, who heads MIT’s Fluid Dynamics of Disease Transmission Laboratory.

Read: How do people get flu?

The findings published in the journal Experimental Fluids stress the importance of facts to understand "the complex pattern of how droplets are dispersed and fragmented during sneezing".

This information, explains Professor Bourouiba, will help researchers predict the spread of infections and diseases through the environment and ultimately prevent them spreading.

So if their sneezing studies can reduce all those nasty airborne infections, what better reason to say, “bless you” when next you a-choo!

Read more:

Symptoms of flu

Diagnosing flu

Preventing flu

flu

 

Ask the Expert

Flu expert

Dr Heidi van Deventer completed her MBChB (Bachelor of Medicine and Bachelor of Surgery) degree in 2004 at the University of Stellenbosch.
She has additional training in ACLS (Advanced Cardiac Life Support) and PALS (Paediatric Advanced Life Support) as well as biostatistics and epidemiology.

Dr Van Deventer is currently working as a researcher at the Desmond Tutu Tuberculosis Centre at the University of Stellenbosch.

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