Leviticus 13:1-3

Then the LORD spoke to Moses and to Aaron, saying, “When a man has a swelling on the skin of his body, a scab, or a bright spot, and it becomes the 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 diseased spot on the skin of his body, and if the hair in the infection has turned white and the infection appears deeper than the skin of his body, it is an infection of leprosy; when the priest has looked at him, he shall pronounce him [ceremonially] unclean.