The priest is to examine the infection on his skin, and if the hair in the infection has turned white and the sore appears to be deeper than the skin, it is a skin disease. After the priest examines him, he must pronounce him unclean.
KJV
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.
ASV
and the priest shall look on the plague in the skin of the flesh: and if the hair in the plague be turned white, and the appearance of the plague be deeper than the skin of his flesh, it is the plague of leprosy; and the priest shall look on him, and pronounce him unclean.