Ultraviolet (UV) radiation is the invisible killer that you can't see or feel. It is strong enough to cause sunburn in as little as 11 minutes on a fine summer day.

UV radiation can be high even on cool and overcast days. This means you can't rely on clear skies or high temperatures to determine when you need to protect yourself from the sun.

A cool or overcast day in summer can have similar UV levels to a warm, sunny day. Sun damage is also possible on cloudy days, as UV radiation can penetrate some clouds, and may even be more intense due to reflection off the clouds.