Leviticus 13:2-8

“When someone has on the skin of his body a swelling, or a scab, or a bright spot, and it becomes an infection of leprosy on the skin of his body, then he shall be brought to Aaron the priest or to one of his sons the priests. The priest shall look at the infected area on the skin of the body, and if the hair in the infection has turned white and the infection appears to be deeper than the skin of his body, it is an infection of leprosy; when the priest has looked at him, he shall pronounce him unclean. But if the bright spot is white on the skin of his body, and it does not appear to be deeper than the skin, and the hair on it has not turned white, then the priest shall isolate the person who has the infection for seven days. Then the priest shall look at him on the seventh day, and if in his eyes the infection has not changed and the infection has not spread on the skin, then the priest shall isolate him for seven more days. The 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 wash his clothes and be clean. “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. And the priest shall look, and if the rash has spread on the skin, then the priest shall pronounce him unclean; it is leprosy.