Leviticus 13:12

Yet if the leprosy increasing increaseth in the skin, and the leprosy covereth all the skin of his flesh, from his head even to his feet, in whatever part the eyes of the priest may look on, in deliberating between cleanness and uncleanness,

AND IF THE LEPROSY BREAK OUT ABROAD IN THE SKIN, AND THE LEPROSY COVER ALL THE SKIN OF THE PLAGUE literally: “all the skin of the plague.” It is generally translated though: “all the skin of him that hath the plague.” As explained further, Ramban also understands the verse to apply only where the leprosy covered the whole body, while the expression all the skin of the plague serves to teach us some new matter, as stated in the text. FROM HIS HEAD EVEN TO HIS FOOT … [HE IS CLEAN]. Now the breaking out of the leprosy is not deemed a symptom of purity, until it spreads over the entire body, except for the places which the Sages enumerated in the Mishnah, which do not prevent a person who has turned completely white [from being pronounced pure]. If so, what is the meaning of the phrase all the skin of the plague [which would indicate that only the area of the plague need be turned white]? Rather, the meaning thereof is as follows: “and the leprosy cover all the skin of the plague and from his head even to his foot.” Scripture is thus stating that the place of the plague and the whole body have turned white, but if the whole body has become white, and the appearance of [the area of] the plague has turned to bohak). Now the verse there concludes that bohak is pure. But Ramban here points out that if the leprosy broke out and covered all the person’s body, except that the original place of the plague turned into bohak, he is impure, since before the rule of the present verse applies, the leprosy must spread also to cover the skin of the plague. The same rule applies even if the skin of the plague became completely healed, as mentioned next in the text. or it became healed, the person is impure.