UVB rays are the shorter wavelengths (290-320) and make up about 5-10% of the rays that reach us. UVB rays affect the skin’s outer layer and are the main cause of sunburn, and also play a key role in the development of skin cancer. The intensity of UVB varies by season, location and time of day.
UVA rays are long wavelength (320-400 nm) and constitute approximately 90-95% of the rays that reach us. UVA rays are weaker than UVB rays, but penetrate more deeply into the skin’s layers. They can contribute to signs of premature aging, such as wrinkles, as well as skin cancer and hyperpigmentation.
A common misconception is that we are safe from UVA rays in the winter or if we are sitting indoors or in the shade. The truth is that UVA rays are present during all daylight hours and even throughout the winter months. Even on a cloudy day in the winter, UVA rays can even penetrate through the clouds and through windows even if we don’t see them. These are the most deceptive as we’re less likely to wear sunscreen when we don’t see the sun.