The reason why you should wear sunscreen even in winter is more important than you think. Many people think that UV rays are strong only in summer, but UV rays continue to exist in winter, and UVA rays in particular penetrate deep into the skin regardless of the season. If these UV rays accumulate, skin aging occurs faster and can lead to wrinkles and loss of elasticity. Also, in winter, UV rays reflected from the snow can reach the skin more strongly, so if you let your guard down, you can easily develop pigmentation. I think sunscreen is essential all year round because UV rays come in through windows even when you are indoors. Just applying a light layer at the last step of basic skin care can keep your skin healthy for a long time, so using sunscreen in winter is essential.