My 10 year old son has a bald spot on the side of his head.

My son recently started getting a bald spot on the side of his head. Seems to be from some head phones he's been wearing. Being 10 years old this seems very strange. We went to the doctor and she said his blood levels are good. Vitim D was a little low though, so he's now on a supplement. I wanted to know if anyone has heard of anything like that, and what more we can be doing to help him. Thanks for your time.