The problem is, we're in the middle of filming, and the story takes place during one day. When we started, the air was warm, and now as we go on it's getting colder and colder and the actor's breath is becoming visible. It wouldn't be a problem if we were shooting chronologically, which we're not for production reasons.
Simply put, in the final film it would look like this: the day begins, then there's a scene with no breath, two scenes with breath, again no breath, then again visible breath, etc.
Any final solution would need to be something that wouldn't be visible on the actors, and if possible, wouldn't kill them
Thanks!