Well, not so much snotty noses, there's (s)not much you can do about that, but the fact that actors never have a hanky or tissue.
Instead, they wipe their nose on their hand or sleeve...or on the shoulder of the fellow actor, their character is hugging, if they are lucky.
It's what seven-year-olds do. It's revolting.
Only once have I seen an actor on stage with a hanky. Zoe Wanamaker obviously had a cold during when I saw her in The Rose Tattoo at the National Theatre but she made blowing her nose part of the performance.
An actor blowing their nose isn't going to break some magical spell, in fact watching them wipe snot on their sleeve or hand breaks the spell, grown-ups (mostly) don't do that.
They must know they are going to get snotty why not be like Zoe, make it part of the performance?