TT #190 · Parshas Tazria · Aliyah 5 · Passuk 30
English: the priest shall examine the affliction. If its appearance is deeper than the skin and it contains thin yellow hair, the priest shall pronounce him unclean; it is a netek, tzaraas of the head or beard.
Chabad.org — Chumash, English translation + Rashi for Vayikra 13:30
Torah Temimah cites Sifra (Toras Kohanim) for excluding depth produced by human action rather than by the condition itself.
Sifra — Vayikra 13, Midrash Sefer
English: Why does Scripture say “its appearance is deep”? One might think that a person could make the lesion appear sunken by cutting or pulling at it and thereby render it impure. The Sifra teaches that the required depth must be “by the hand of Heaven”—arising from the condition itself.
Textual derivation
The legal sign must arise naturally from the lesion; deliberately creating a sunken appearance does not satisfy the Torah’s criterion.