The issue of chapped lips is, simply put, an over drying of the skin on your lip. Cold air, low humidity, sunlight and even strong winds can cause this excessive dryness.
The reason why your lips can dry out so quickly - faster than other areas of your skin - is due to the fact that the skin on your lips is actually a mucus membrane. Without getting too technical, this means that the skin on your lips is much thinner and more delicate, so it's more vulnerable.
In addition to being vulnerable, your lips don't have a protective layer that skin on other areas of your body have. So when your lips dry, the membrane cracks and the cracks actually let moisture out and so the cycle continues and continues (this is where the over drying comes in).
It's pretty easy to see why the skin on your lips is so attune to dryness, but it's also easy to take care of this pesky problem. Enter lip balm. Oil-based balms - those that have beeswax or petroleum - help to hold moisture in. Use this rule of thumb, if it's cold enough to wear a coat, then it's cold enough to put on a layer of lip balm. Although, for me, I have to say that lip balm is an everyday kind of thing... just like our other skincare essentials (sunscreen, exfoliants and antioxidants).