Charles Ellicott 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. —If, on inspecting it again at the end of the seven days’ seclusion, the priest finds that the spot has spread, it was evident that the blood was corrupted, and that the disease began to develop in the body.

It is a plague. —That is, of leprosy. The word “leprosy,” which is missing from the text here, is still preserved in some of the ancient versions.