|Sun damaged skin. The red area is where the man did not|
We can feel infra-red radiation through temperature sensors in the skin, but we cannot feel ultraviolet radiation that causes damage to our skin. Therefore, we have to protect our skin by using a sunscreen.
Often people believe that they do not need protection on a cloudy day, but a thin stratus of clouds does not stop ultraviolet radiation from reaching the earth surface. A thin cover of clouds may attenuate only about 20% of the light.