Leviticus 13:6-8

6The priest shall then look at him again on the seventh day, and if the infected area has faded and the infection has not spread on the skin, then the priest shall pronounce him clean; it is only a rash. And he shall 1wash his clothes and be clean.

7“But if the rash spreads farther on the skin after he has shown himself to the priest for his cleansing, he shall appear again to the priest. 8And the priest shall look, and if the rash has spread on the skin, then the priest shall pronounce him unclean; it is leprosy.