Leviticus 13:6-8

6On the seventh day the priest is to examine them again, and if the sore has faded and has not spread in the skin, the priest shall pronounce them clean; it is only a rash. They must wash their clothes, and they will be clean.

7But if the rash does spread in their skin after they have shown themselves to the priest to be pronounced clean, they must appear before the priest again.

8The priest is to examine that person, and if the rash has spread in the skin, he shall pronounce them unclean; it is a defiling skin disease.