This is a practice that most campers ignore, which is why they will need to throw away a perfectly good mattress for camping after a while. Experts suggest that you sustain yourself from this desire. By blowing into the mattress with your mouth, you are introducing bacteria and moisture inside the mattress. This could cause moisture freezing and could cause you to feel extremely cold while sleeping in low temperatures. Even worse, you could even grow mold inside the mattress. Needless to say, there is no way of getting the mold out so you would be stuck with the burden of buying a new one or sleeping on a smelly old mattress. If you insist on adding extra air, it might be worth it to you to buy a hand pump. This is much safer and saves you time and energy.