Sunlight that reaches us is made up of two rays; UVA and UVB, UVA is a long wavelength ray and UVB is a short wavelength ray. UVA rays can penetrate deeper into our skin layers and causes wrinkles premature aging and also suppression of immune system. It is present throughout the year during daylight hours. They can penetrate glass and clouds which mean the application of sunscreen during winters is as important as any other season.
UVB rays can burn the superficial layer of the skin. Unlike UVA rays, the intensity of UVB rays varies by season, location and time of day (10AM-4PM are considered peak hours). UVB rays play a crucial role in burning, tanning and in the development of skin cancer. Unlike UVA rays, UVB rays do not penetrate glass.