You'll know when you start seeing it fall out. If there's a family history of male pattern baldness then it's likely, but there's no guarantee. Test converts to dht via the 5 alpha reductase enzyme. 5AR is everywhere and the body except muscle and has a high concentration in the scalp. Therefore if your prone to it you elevate your chances by using aas. Google Propecia or Fin and read before you consider those products. Lots of sides not to mention law suits.