You use an exfoliant on your face and skin and it's just as important to use an exfoliant for your lips.
To really cure a constant chapped lips problem, exfoliating away the rough, dried skin is essential in helping fresh layers of skin come through.
Why use sugar? Sugar tends to be smaller in size than other exfoliants, making it ideal for sensitive or delicate skin. And, because it's much gentler on skin, it's perfect for removing layers of flaky skin without running the risk of irritation or abrasion. Plus, the natural chemical exfoliant in sugar enhances its efficacy while still retaining moisture.
How often should you use a lip scrub? Normally once a week is sufficient but with a sugar scrub, if your lips are extremely chapped, using a sugar scrub once a day until you get your lips soft and beautiful again is acceptable. It's also good to use a good moisturizing lip balm after you exfoliate.
Especially if you're in the wind and sun a lot then using a lip scrub once a week is a good thing to do to keep those lips supple.