There are many things an author can describe while two characters are speaking to each other. These includes hand gestures, facial movements, and the one I want to talk about today: breathing.
People who are alive breathe constantly and most rarely notice they’re doing so. As long as it’s not done too often, there’s nothing wrong with a character doing the following:
1) Not breathing: A character can say they can’t breathe because they have been exercising or are panicked in some way. If done too often of course, readers might think the character has asthma.
2) Taking deep breaths. A character might take a deep breath in order to deliberately pause the conversation (for example, to collect their thoughts). If they do it too often, once again –> asthma.
3) Exaggerating breaths. A character can exaggerate an exhale as a way to show anger or frustration. Be careful with this one. If done too often, readers might think the character is a horse.
What is a problem is if your characters are doing this:
1) Taking a normal breath. Seriously? When is the last time you noticed that you inhaled normally?
2) Noticing someone else take a breath. Once again, unless that someone is gasping for air, YOU WOULD NOT NOTICE THIS unless, maybe, they were sleeping and you were watching their chest rise and fall in an effort to make sure they’re still alive.
3) Taking a breath while or immediately after swallowing. Try it. It’s impossible. You cannot breathe while swallowing and always exhale after you do.
4) Breathing out in a manner that causes a gale force wind effect. I haven’t seen this often but if your character breathes out hard enough to blow the bangs off his face, they’d better be hanging below his nose. Otherwise, it’s not breathing; it’s blowing.