Nasal breathing is preferred for breathwork exercises like box breathing, but mouth breathing can be a viable alternative for individuals with severe nasal occlusion.

“Again, if at all possible, do all of this breathing through the nose. For those of you that have a severely occluded nose, the recommendation always is to breathe through your nose more. But I do realize that for some people, it's really uncomfortable to breathe through the nose because they have such an occluded nasal pathway. And for you folks, doing some of this breathing through the mouth can probably suffice. But if at all possible, do the breathing through the nose.”