UV rays are electromagnetic waves that travel from the sun towards the earth. UV waves are divided according to wavelength. The wavelength has something to say in relation to where in the skin the UV rays hit and therefore which structures in the skin are affected.
UVB rays are what make the skin brown and sunburned. These are strongest in summer and in cloudless weather. Protection against UVB rays is indicated with SPF. UVA rays are mainly the cause of age-related changes in the skin. The UVA rays are so to speak constant all year round. They penetrate the cloud layer and windows.
UVA protection is indicated with the UVA mark - UVA with a circle around it or with the indication UVA-PF.