It’s a good idea to work lip protection into your daily skin care regimen even if you spend most of your time indoors. Outdoor factors such as sun, wind and cold can speed up the rate of lip moisture loss. But lips also frequently suffer indoors from a lack of moisture in centrally heated or air-conditioned rooms where the relative humidity is low. Dryness is also the enemy when a winter cold or flu strikes. Lip irritation can even be caused by certain types of food, cosmetics and cigarette smoke.