It's common to get dry, chapped lips during the Winter, but what about cracks at the corners of your mouth that don't seem to go away no matter how much lip balm you apply? I've heard that this could be a symptom of a vitamin deficiency, so I decided to do some research.
Indeed, persistent cracking at the corners of the lips could be a sign that you're not getting enough vitamin B — in particular, folic acid (B9) and riboflavin (B2). This isn't anything to freak out about, but if you think your diet might be lacking, try taking a multivitamin or vitamin B complex supplement. Or just increase your intake of foods rich in B vitamins and see if that helps. You can also soothe the cracked areas with ointments like Vaseline or Neosporin.
If the problem persists, talk to your doctor to see if you might have a more serious problem with anemia or a common fungal infection called angular chelitis.