Leviticus 13:1

When a man shall have in the skin of his flesh a rising, a scab, or bright spot, and it be in the skin of his flesh [like] the plague of leprosy; then he shall be brought unto Aaron the priest, or unto one of his sons the priests:

And the priest shall look on the plague in the skin of the flesh: and [when] the hair in the plague is turned white, and the plague in sight [be] deeper than the skin of his flesh, it [is] a plague of leprosy: and the priest shall look on him, and pronounce him unclean.