Charles Ellicott Commentary Leviticus 13:55

"and the priest shall look, after that the plague is washed; and, behold, if the plague have not changed its color, and the plague be not spread, it is unclean; thou shalt burn it in the fire: it is a fret, whether the bareness be within or without." — Leviticus 13:55 (ASV)

And the plague be not spread. —Better, though the plague has not spread. If after the washing of the affected spot the priest finds that its appearance has not changed, it must nevertheless be burned, since the retention of the suspicious color indicates that it is leprosy.

It is fret inward, whether it be bare within or without. —Better, it is a corroding in its fore baldness or in its back baldness. (See Leviticus 13:42-43.) That is, though it has not spread in breadth, the disease has eaten into the fabric, either on the upper side, which is compared to the forehead, or into the underside, which is compared to the back part of the head in human head-leprosy.