Wear Your Sunscreen, But Make Sure It’s Fresh!
A quick search of the web for "sun skin cancer" leads right to the Web MD site, which explains how the sun damages your skin and how it causes cancer.
The Mayo Clinic recommends to not use sunscreen that is past it's expiration date or older than 3 years.
As a habit in our house, when we renew our fishing licenses, we rid the cabinets of any remaining sunscreen and buy a new tube.
Now if I could only remember to change the dang air conditioning filter on a regular basis!