Mucus is our body's greatest hero according to the author. Mucus is our body's greatest hero according to the author.

I would say there are other "heroes" in the human body, but if the author or you aren't of the same opinion, you can leave it out.

Mucus is best known for being the stringy slime drippingthat drips from noses and vicithe viscous goop hacked/coughed up by sickening airways. Mucus is best known for being the stringy slime that drips from noses and the viscous goo hacked/coughed up by sick airways.

sickening = disgusting. While that also works in this context, I do believe you intend to refer to the airways of sick people.

Mucus is best known foras the stringy slime drippingthat drips from noses and vicious goopthe viscous goop that is hacked up by sickeninginfected airways. Mucus is best known as the stringy slime that drips from noses and the viscous goop that is hacked up by infected airways.

Because you wrote "that drips from" I think it is best to say "that is hacked up" so that the sentence structure/pattern is consistent. (This is called parallel structure, by the way.) "Infected airways" sounds more natural to me than "sick airways."

Mucus coats the surfaces of the intestines, eyes, mouth, nasal cavity, and ears, thus playing an important physiological roles. Mucus coats the surfaces of the intestines, eyes, mouth, nasal cavity, and ears, thus playing an important physiological role.

It hydrates, cle and cleans organs, supports good microorganisms, and repels invaders. It hydrates and cleans organs, supports good microorganisms, and repels invaders.

How you have said it suggests that the mucus hydrates, cleans, and supports good microorganisms.

Most of these functions come fromare thanks to mucins. Most of these functions are thanks to mucins.

or "Most of these traits derive/come from mucins"

Mucins give mucus its gel-like qualitiesy. Mucins give mucus its gel-like quality.

Quality and qualities work, but I think "quality" fits better here because your entry is not about gel.

In airways, hHaving too much mucus might causbecome harm under certain conditionsful when coupled with certain conditions that affect the airway: asthma, cystic fibrosis, and chronic obstructive pulmonary disease. Having too much mucus might become harmful when coupled with certain conditions that affect the airway: asthma, cystic fibrosis, and chronic obstructive pulmonary disease.

Just more natural phrasing

In airways, hHaving too much mucus might causbe harm underful when coupled with certain conditions:, such as asthma, cystic fibrosis, and chronic obstructive pulmonary disease. Having too much mucus might be harmful when coupled with certain conditions, such as asthma, cystic fibrosis, and chronic obstructive pulmonary disease.

However, in the intestine, having too much mucus in the intestine is not a problem. However, having too much mucus in the intestine is not a problem.

This sounds more natural to me.

Having too much would be better rather thanis better than having too little. Having too much is better than having too little.

HIn fact, having too much would be better rather thanis better than having too little. In fact, having too much is better than having too little.

I think adding "In fact" makes the sentences connect/flow better.