The action has to be violent to generate enough pressure to expel whatever has lodged in your nostrils or sinus cavity.
Other actions involving the lung and core muscles are similarly violent like coughing (can crack a rib), hiccups, vomiting (can tear the inner lining of the esophagus).
I imagine you reflexively close your eyes as a defense mechanism, but you can force yourself not to do so.
Sneezing is not exactly the primary purpose of the nose; it’s a full-body defense mechanism for when you breathe in particles you’re not supposed to, like allergens. And it requires tons of different muscle groups, including your abs and chest. Instead of comparing it to other bodily functions that aren’t defense mechanisms, it makes more sense to compare it to defense mechanisms such as vomiting, which also takes a lot of bodily effort to do.
Airways are critical to our survival. While we put a lot of things into our mouths nothing except air is supposed to go up the nose. Stuff tickling in the nose is a definitive NO! so it’s a good idea to blow whatever that is out as fast as possible.
Anything in the mouth might be food, so the reaction only happens when the whole intricate process of swallowing goes wrong. The coughs from inhaling food are about as hard to suppress as a sneeze and reach impressive air flow speeds (200-500km/h)
It’s a defensive reaction taking place in one of the most vulnerable parts of the body to infection and injury. Anything irritating gets evicted, fast. The one time in my life I went from asleep to wide awake in seconds, my cat who slept beside my pillow at night, managed to insert one long whisker well up my nose.
I’d simplify it down to sneezing being a reflex, largely of of your control.
You’d also need to pull over to (safely) react to a patellar reflex, punching, pinching, flinching, etc. Some more than others, sure, but you don’t want to be doing other things when you don’t have control over your body (when you’re responding via reflex).
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