The kohen is to examine him on the seventh day. If it has spread in the skin, then the kohen is to pronounce him unclean. It is the plague of tza'arat.
“When a man has a swelling on the skin of his body or a scab or a bright spot, and it becomes the plague-mark of tza'arat in his flesh, then he shall be brought to Aaron the kohen, or to one of his sons, the kohanim.
But if the kohen examines it and sees there is no white hair in the bright spot, and it is not lower than the skin but is faded, then the kohen is to isolate him seven days.
If the bright spot stays in its place, and has not spread in the skin but is faded, it is the swelling from the burn, and the kohen shall pronounce him clean, for it is merely a scar from the burn.