Why do you have a bald spot on your beard?

Answer 1

This sounds like patches of either alopecia, or a fungal infection affecting the beard hair follicles, which can cause exactly these symptoms. Some people might use hair growth formulas like Regaine, but this is unlikely to have any effect (although it will do no harm if you want to try it on your beard) and I would suggest you see your GP in order to get this diagnosis confirmed and treatment begun if applicable. Most such cases are self-limiting anyway and growth returns to normal, but this can take many months, so the sooner you get it checked out the better ;D.

Answer 2

Usually it's because the hair follicles have been damaged - a scar from an accident or a childhood disease such as chicken pox, for example. Scar tissue isn't the same as skin, and has no hair follicles.