No — ordinary hat wearing does not cause hair loss. The follicle gets its blood supply from below the skin, and a hat resting on your head does not affect it.
Transcript
Hats don't cause baldness. There's no mechanism for it and no evidence for it. Your follicles are fed from underneath by blood, not from the air. What genuinely can pull hair out is tension. Braids too tight, the same bun every day, extensions. That has a name, traction, a alopecia, and unlike a hat, it leaves a pattern along the hairline you can actually see.
The kernel of truth behind the myth is traction: anything that pulls hair tight for long periods — very tight braids, extensions, or headgear that constantly tugs — can damage follicles over years. That is traction alopecia, and it is about sustained pulling, not covering.
If your hair is thinning under a hat, the hat is probably where you noticed it, not why it happened. A doctor can tell you what is actually driving it.