Lots of things can cause a body to be deficient in B vitamins, but if you haven't been eating the best diet lately, it could just be you simply need to focus on increasing B-rich foods or start popping a B-complex supplement to boost your levels. Like iron, cracked lips can be a sign of low vitamin B12, for example. A lack of B12 can cause dizziness, rapid heart rate, fever, significant weight loss, tiredness, confusion, depression, appetite loss, poor digestion and an array of tactile malfunctions. Not pretty.
So either get some B-complex supplements, or do some exploring to discover what kinds of foods you could be missing out on. And if B vitamins and iron don't fix you right up, try adding other nutrients to your diet -- whether through foods or through supplements -- to see if you aren't running low on something else. For example, vitamin E liquid capsules can even double as a supplement-rich balm. Just pop one open and smooth it over stressed-out lips. If you're still having a significant problem, however, you may need to visit a doctor.