What Could Blad Patches On Hair Suggest?

I am trying to figure out if a bald patch of hair on my left side is due to me wearing a metal barrett day in and day out every day. Or from a mild thyroid condition I was diagnosed with. I am taking thyroid meds now, but even when I wasnt the hair did not continue to be gone, etc. So, basically how would I know if its actual "medical hairloss" or a barett???