androgenetic alopecia
"I am 23 and started noticing a bit of hairline recession at about 21. My hair was slightly thinning around the temples, but never in the front. 

I am 1 month into 1mg of propecia daily, and I do not think it has affected the temples areas, but the front of my hair has started thinning in the last couple weeks. In bright lighting, i can see pretty far back onto my scalp when looking from the front (it looks like my temples did about a year ago), and it's scary. I don't think I am noticeably shedding anymore than I used to, but I can't run my fingers through my hair without getting at least at couple hairs. Overall I have definitely lost more hair at an accelerated rate. Hopefully this is just an initial shed."