"The cracking and crusting can be a result of lack of humidity, causing the lips to become dry. Cracking of the lips may be the result of loss of pliability of the tissue and build up of dried saliva, and/or bacterial and fungal overgrowth. The lips become dry and crack, and if you continue to lick them, the air dries the saliva on the surface and the bacteria and fungus colonize the dried out surface and the cracks (fungus like Candida sp. require a scaffolding to colonize and the dried skin (keratin) provide such). The lips are dry and not pliable and can bleed, thus adding to the problem. As most mothers used to say "don't lick your lips" - there was a reason. "