John Gill Commentary Leviticus 13:22

"And if it spread abroad in the skin, then the priest shall pronounce him unclean: it is a plague." — Leviticus 13:22 (ASV)

And if it spread much abroad in the skin Upon viewing it on the seventh day, though it is not expressed, the swelling or bright spot; or "in spreading spread"; (See Gill on Leviticus 13:7); which Ben Gersom interprets, not of the skin of the flesh, but of the ulcer:

then the priest shall pronounce him unclean ; even though there are no white hairs in it, nor is it lower than the skin, yet is not at a stand or contracted, but spreading:

it [is] a plague ; or stroke; it is one sort of a leprosy, and such an one as makes a man unclean in a ceremonial sense.