Constitutional Carry: With permitless carry, what decides whether or not somebody is prohibited from firearms or not?

I keep reading about how Consitutional Carry is permitless, but how individuals who are prohibited from buying/carrying will still be prohibited.My question is, how exactly will these people will be prohibited if no permit is required for carrying?Thanks guy, just trying to see which side of the fence I fall on. (Concealed permit vs Permitless) via /r/CCW http://ift.tt/1NfaGqi