Albert Barnes Commentary Leviticus 13:12-17

"And if the leprosy break out abroad in the skin, and the leprosy cover all the skin of [him that hath] the plague from his head even to his feet, as far as appeareth to the priest; then the priest shall look; and, behold, if the leprosy have covered all his flesh, he shall pronounce [him] clean [that hath] the plague: it is all turned white: he is clean. But whensoever raw flesh appeareth in him, he shall be unclean. And the priest shall look on the raw flesh, and pronounce him unclean: the raw flesh is unclean: it is leprosy. Or if the raw flesh turn again, and be changed unto white, then he shall come unto the priest; and the priest shall look on him; and, behold, if the plague be turned into white, then the priest shall pronounce [him] clean [that hath] the plague: he is clean." — Leviticus 13:12-17 (ASV)

The disease indicated here appears to be what is now known as Lepra commonis, the common White Leprosy, or Dry Tetter. It first shows itself in reddish pimples, the surface of which becomes white and scaly, spreading in a circular form until they meet each other and cover large patches of the body. It hardly affects the general health and mostly disappears on its own, though it often lasts for years.

From his head even to his foot, wheresoever the priest looketh – The first appearance of Lepra Commonis may take place in any part of the body, though especially at the larger joints of the limbs. However, the spots of elephantiasis are almost always first seen on those parts that are habitually exposed: the face, ears, and hands.

(Leviticus 13:14)

Raw flesh – See Leviticus 13:10.

(Leviticus 13:15)

Boil – Probably an ulcer. In Job 2:7, Deuteronomy 28:27, and Deuteronomy 28:35, it seems highly probable that the word expresses the ulcers of elephantiasis.