I normally don't wear a hat when I go outdoors. My mom on various occasions told me to wear a hat for protection from the sun, and today I finally wore a fishing hat (which I had around for some unknown reason). Today my scalp got sunburned. This has never happened before, and I cannot think of any other possible reason besides the hat. It's like the hat is an antihat!
(I guess what happened is my hear stuck together from sweat under the hat and this let far more sun get to my scalp during the times when I wasn't wearing the hat.)