I just finished reading James Nestor's fascinating book Breath: The New Science of a Lost Art: highly recommended! All singers will benefit from this book. Among many other recommendations, Nestor extols the benefits of nasal breathing, which has also been recommended by numerous cultures around the world for centuries. This is trickier for singers since mouth breathing is faster and often we don't have a lot of time in-between phrases for a nasal breath. But if you read the book I bet you'll be sold on breathing through your nose more often.
In the past I've often told singers to breathe through the nose when not singing, and also when warming up if one is having placement issues, has allergies or 'gunkiness' going on, or is singing flat. In the past I said breathe through the mouth when singing the rest of the time since it's faster. I've modified my thinking now: all the time now when warming up I breathe through my nose as much as possible, and when singing [if there's enough time in-between phrases or sections] I take a nose breath in there as well.
As singers we've learned to breathe deeply into the diaphragm and we've learned to slow the exhalation as we sing with good breath support. So we're ahead of the rest of the world on these healthy breathing practices. Check out the book and his site and you'll learn some new methods that could change your singing life for the better.