Do you only wear sunscreen during the summer? Trip to the beach?
Winter? Snow can reflect up to 80% of UV rays. Going on that ski vacation, the higher the altitude, the stronger the exposure.
Indoors? Windows and fluorescent bulbs can let through UV rays as well. So unless you work in a dark windowless room for hours, apply that SPF!
Cloudy? UV rays can still penetrate through the clouds.
Lesson of the day, be safe and prevent premature wrinkles, slather that sunscreen and protect your skin all year round!