Lower than the skin - Rather, reaching below the scarf skin.
Related Commentaries of Leviticus 13:20
Leviticus 13:20-21
20 And if, when the priest seeth it, behold, it be in sight lower than the skin, and the hair thereof be turned white; the priest shall pronounce him unclean: it is a plague of leprosy broken out of the boil.
21 But if the priest look on it, and, behold, there be no white hairs therein, and if it be not lower than the skin, but be somewhat dark; then the priest shall shut him up seven days: