There are a few things that are known to induce hair loss, but wearing hats isn't one of them -- even if you wear one every day. Here's the truth about that old wives' tale.
In this video from the Mental Floss YouTube channel, Craig Benzine explains the leading causes of hair loss: poor nutrition, drugs, infection, pregnancy, trauma, and the biggest factor of them all, genetics. There is, however, a condition known as traction alopecia that causes hairlines to recede due to, well, consistent traction or rubbing. The skin gets damaged and scars over the hair follicles so nothing can grow there anymore. Wearing tight ponytails, hair barrettes, or helmets on a regular basis can put you at risk. But only wearing a hat isn't enough to cause that unless it was extremely tight on your head.
That said, wearing hats can speed up the balding process if you're already losing your hair due to genetics or other causes. Taking the hat off can pull out hairs, and if it's too tight, adjusting it can also yank some out. So wear your hats just a little bit loose and you'll be fine.
Do hats cause balding? [YouTube]