Frostbite!
While the frost is nipping at your nose, the sun can still be damaging your skin - because it's not heat that causes skin cancer, but radiation. In winter, there are fewer ultraviolet B ("burning") rays, but the number of ultraviolet A (UVA) rays that reach the earth's surface remains about the same.
Snow and ice are powerful sun reflectors; higher altitudes increase your exposure to the sun's radiation.
Advice: