Although they don't cause painful sunburns like UVB rays, the sun's UVA rays can't be felt and penetrate the skin to cause long term damage in the form of wrinkles and skin cancer (remember A for ageing and B for burns).
These UVA rays can pass through light cloud or glass, so sitting by a window or driving in our cars exposes us to these harmful rays.
Always have a good sun protection strategy which includes a good sunscreen and a shade device, such as a hat or a Joopy shade for your car.