[katieHaylor (OP)]

Mike asks:

I find that I am able to prevent an oncoming sneeze by pressing my tongue against my palate. Why?
Also, why is it impossible to open one’s eyes whilst sneezing?

What do you think?

[chris]

why is it impossible to open one’s eyes whilst sneezing?

It's not impossible to open your eyes while sneezing, but it is difficult.

This is a reflex, although the intended purpose is not, as the myth commonly goes, to prevent your eyes popping out. There is no increase in pressure behind the eyes during sternutation (the proper word for sneezing). This is because the rush of air is confined to the respiratory passages, so you are not in danger of dislodging your eyeballs.

Instead, I think the reason is more mundane and practical. Tears from the lacrimal gland run across the front surface of the eye from the upper outer region of the orbit towards the inner aspect of the lower eyelid. If you look at this part of your eye in a mirror you will be a small black "dot" on the lower eyelid next to your nose.

This is called a "punctum", which is latin for "small distinct point" but might as well be translated as "plug hole"; this is the exit point for tears, which drain through this hole into the nasolacrimal duct, which carries the tear fluid into the nasal cavity. This is why your nose runs and you need to blow it, or reach for a tissue, when you cry, because the excess fluid runs out of your nostrils.

The act of screwing up your eyes when you sneeze compresses and closes the punctum and the upper part of the nasolacrimal duct. This keeps the pressure high in this area preventing the pressure wave from a sneeze blowing muck and germ-laden mucus from your nose into your eyes.

Arguably, an eye full of snot would obscure vision to a much greater extent in the aftermath than a momentary near-involuntary eye closure for the duration of the sneeze, which is probably why we've evolved to do this.

For the record, you can keep your eyes open during a sneeze - or at least I have managed it (in the name of scientific investigation) - by force of will, although I wouldn't recommend it if you have a choice!