Leviticus 13:6-8

6The priest will examine him again on the seventh day. If the sore has faded and has not spread on the skin, the priest is to pronounce him clean; it is a scab. The person is to wash his clothes and will become clean.

7But if the scab spreads further on his skin after he has presented himself to the priest for his cleansing, he is to present himself again to the priest.

8The priest will examine him, and if the scab has spread on the skin, then the priest must pronounce him unclean; he has a serious skin disease.