Charles Ellicott Commentary Leviticus 13:11

"it is an old leprosy in the skin of his flesh, and the priest shall pronounce him unclean: he shall not shut him up, for he is unclean." — Leviticus 13:11 (ASV)

It is an old leprosy. —Either of these symptoms showed that it was the reappearance of the old disease, and rendered quarantine needless. The priest is, therefore, to pronounce him unclean at once.