29 And if a man or a woman have a sore on the head or on the beard, 30 and the priest look on the sore, and behold, it looketh deeper than the skin, and there is in it yellow thin hair, then the priest shall pronounce him unclean; it is a scall, the leprosy of the head or the beard. 31 And if the priest look on the sore of the scall, and behold, it is not in sight deeper than the skin, and there is no black hair in it, the priest shall shut up [him that hath] the sore of the scall seven days. 32 And when the priest looketh on the sore on the seventh day, and behold, the scall hath not spread, and there is in it no yellow hair, and the scall doth not look deeper than the skin, 33 he [that hath the sore] shall shave himself; but the scall shall he not shave; and the priest shall shut up [him that hath] the scall seven days a second time. 34 And the priest shall look on the scall on the seventh day, and behold, the scall hath not spread in the skin, nor is in sight deeper than the skin, then the priest shall pronounce him clean; and he shall wash his garments, and be clean. 35 But if the scall have spread much in the skin after his cleansing, 36 and the priest shall look on him, and behold, the scall hath spread in the skin, the priest shall not seek for yellow hair: he is unclean. 37 But if the scall have in his sight remained as it was, and there is black hair grown up therein, the scall is healed: he is clean; and the priest shall pronounce him clean.

Matthew Henry's Commentary on Leviticus 13:29-37

Commentary on Leviticus 13:18-44

(Read Leviticus 13:18-44)

The priest is told what judgment to make, if there were any appearance of a leprosy in old sores; and such is the danger of those who having escaped the pollutions of the world are again entangled therein. Or, in a burn by accident, verse 24. The burning of strife and contention often occasions the rising and breaking out of that corruption, which proves that men are unclean. Human life lies exposed to many grievances. With what troops of diseases are we beset on every side; and thy all entered by sin! If the constitution be healthy, and the body lively and easy, we are bound to glorify God with our bodies. Particular note was taken of the leprosy, if in the head. If the leprosy of sin has seized the head; if the judgment be corrupted, and wicked principles, which support wicked practices, are embraced, it is utter uncleanness, from which few are cleansed. Soundness in the faith keeps leprosy from the head.