A plague upon the head or the beard - This refers to a disease in which, according to the Jews, the hair either on the head or the chin dropped out by the roots.

If a man or a woman hath a plague upon the head or the beard. Any breaking out in those parts a swelling, scab, or spot, on a man's beard or on a woman's head; or on the head of either man or woman; or on a woman's beard, if she had any, as some have had though not common.

Leprosy upon the head or chin. - If the priest saw a mole upon the head or chin of a man or woman, the appearance of which was deeper than the skin, and on which the hair was yellow (צהב golden, reddish, fox-colour) and thin, he was to regard it as נתק. Leprosy on the head or chin is called נתק, probably from נתק to pluck or tear, from its plucking out the hair, or causing it to fall off; like κνήφη, the itch, from κνάω, to itch or scratch, and scabies, from scabere. But if he did not observe these two symptoms, if there was no depression of the skin, and the hair was black and not yellow, he was to shut up the person affected for seven days. In בּו אין שׁחר (Leviticus 13:31) there is certainly an error of the text: either שׁחר must be retained and אין dropped, or שׁהר must be altered into צהב, according to Leviticus 13:37. The latter is probably the better of the two.

If a man or woman have a plague upon the head or the beard;

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, ver. 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.