Did you know that clouds filter out sunlight but not UV rays that cause premature aging and cancer? Clouds block as little as 20% of UV rays so you are still getting 80% of the sun's harsh effects even on the most cloudy of days. A lot of people have the misconception that it must be hot to incur sun damage but this couldn't be further from the truth. UV rays are independent of temperature, so you can get just as much sun damage on a cold, sunny day than you can a hot summer one.
Your sun protection should become a daily habit!