Leviticus 13:31

13:31 But if the priest examines the scall infection and it does not appear to be deeper than the skin, and there is no black hair in it, then the priest is to quarantine the person with the scall infection for seven days.

Leviticus 13:37

13:37 If, as far as the priest can see, the scall has stayed the same and black hair has sprouted in it, the scall has been healed; the person is clean. So the priest is to pronounce him clean.