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We're getting outside of my meagre knowledge so hopefully a 'doc or other biology-inclined specialist will swing by. I know that in e.g. the lungs it's the only way to evacuate junk (e.g. dead viruses and immune cells), but for the nose I don't know if it's functional or if it's just a side-effect of the inflammation of the mucosa which is not deadly enough to get weeded out by natural selection.

But what is the function for this excess production of this mucus?

Is this actually a useful mechanism against diseases like the common cold? Or is it just a trait carried over from the likes of the fish you mentioned in your comment, which actually utilised the mucus production as a defence mechanism?

Never ceases to amaze how someone always knows this niche information and can produce a great link to explain exactly like they mean as you did with the Richard Hammond video. On top of that, make it super easy to understand and enjoyable too!

Great reply, thank you.

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there may not even be too much of an in-between step to begin with. whether it is baby steps or a leap, it is both difficult to imagine

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That's a helpful picture. Thank you! It blows my mind that they can manufacture physical bumps smaller than the wavelength of light.

pretty sure this is false in most cases. What really happens is the bacteria cant cling on to anything and they get washed away. Dish soaps have antibiotics though which will kill bacteria.

A good example is toothpaste. All the bacteria in your mouth don't just die. In fact that would be bad, because something worse would take over.

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> or do you have like a secret mucus receptical that just decides to empty into your sinuses?

Mucus is a compound built from a small amount of specific proteins (mucins) and a lot of water.

So "all the snot" mostly comes from the water in your body, the gelling agent can be produced in pretty small quantities by mucous membranes, specifically the nasal mucosa, and even more specifically the goblet cells of the nasal mucosa. The nasal mucosa produces small quantities of mucin on a permanent basis (like other mucous membranes) in order to protect itself, trap debris, and move things along, but when you suffer from an infection of the nose one of its (possible) reaction is to ramp up mucin production, leading to significant amounts of mucus.

Hagfishes are a good way to demonstrate how fast and how much mucus can be produced as they use it as a defense mecanism (their body is lined with mucin glands, and when threatened they start releasing it in the environment, which is water): https://www.youtube.com/watch?v=t5PGZRxhAyU

An other (maybe somewhat less gross) example is making jellies (as in gelatin desserts not fruit preserves). "Standard firmness" for gelatin products is apparently 1/4 ounces (30g) gelatin to 2 cups (472mL = 472g) water. That's a 15:1 ratio of water to gelatin by mass[0], and that sets hard, it's not runny like mucus is.

[0]: note that "ready" flavoured gelatins (e.g. your jello) will have a much lower ratio, because the powder contains sugar and flavorants, not just gelatin

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