TT #180 · Parshas Tazria · Aliyah 5 · Passuk 27
English: The priest shall examine him on the seventh day. If the lesion has spread in the skin, the priest shall pronounce him unclean; it is a tzaraas affliction.
Chabad.org — Chumash, English translation + Rashi for Vayikra 13:27
Torah Temimah cites Sifra (Toras Kohanim) for the exclusion of living flesh as a qualifying impurity sign in this case.
Sifra — Vayikra 13, Midrash Sefer
English: This lesion does not become impure through the sign of living flesh at the initial examination, at the end of the week, or after release.
Textual derivation
Living flesh is not a qualifying impurity sign in this particular case.