TT #231 · Parshas Tazria · Aliyah 7 · Passuk 42
English: But if a white-reddish lesion appears on the bald area or the front bald area, it is an eruptive tzaraas on his bald area or front bald area.
Chabad.org — Chumash, English translation + Rashi for Vayikra 13:42
Torah Temimah cites Sifra (Toras Kohanim) for spreading as an impurity sign in bald areas.
Sifra — Vayikra 13, Midrash Sefer
English: The word “spreading” teaches that spreading is an impurity sign for a lesion on the bald area.
Spreading can independently establish impurity.
Spreading is a recognized impurity sign for lesions in the bald area.