: We have sebaceous glands in our skin , from which a kind of oily substance comes out and mixes with sweat and spreads all over the skin. As a result, the skin does not crack. As the amount of water vapor in the air decreases in winter, our sweating decreases. Moreover, since it is cold all around, sweat is not required for body heat release. The oily substance from the sebaceous gland cannot spread properly to the skin of the body. The dry areas of the body then wrinkle and rupture. The skin of the lips is thinner than other parts of the body. In addition, the hot air inhaled dries the lips more so that the lips are just below the nostrils. This is why the lips crack more in winter than other parts of the body.