Winter weather brings less humidity, less vitamin D, lower temperatures, and brisk winds, which all affect how much moisture your skin receives and retains, making your skin drier. In the winter, you’re constantly switching from cold weather outside to forced air and heat inside, which decreases humidity indoors and causes dry skin. Vitamin D from sunlight is a natural anti-inflammatory, and you are exposed to much less vitamin D in the winter because you spend less time outside in the sun.