If I ever get skin cancer, Iโ€™ll blame it on the time I burned myself so badly I thought my face was going to peel off. Hiking high up on Mount Rainier, in Washington, where the snow reflects light onto oneโ€™s face from all directions and the frigid air keeps skin numb to the injury, I put on SPF 100 at dawn and didnโ€™t think about it again. The next morning I was so inflamed it hurt to smile.

To understand why people like me make such stupid and consequential mistakesโ€”one in five of us will get skin cancer, despite most cases being preventableโ€”last year a trio of dermatologists at Northwestern University asked its patients to take a quiz about sunscreen.