Many things. From running and getting wind chapped, to dehydration to getting them dry when you mouth breathe when you have a cold.
Chapped Lips. You may think of chapped lips as something that only happens in the winter. But the truth is, unless you take special care, your lips can get dry, sore, and scaly any time of year. Http://www. Webmd. Com/beauty/why-your-lips-are-chapped#1.