וְכִֽי־יִרְאֶ֨ה הַכֹּהֵ֜ן אֶת־נֶ֣גַע הַנֶּ֗תֶק וְהִנֵּ֤ה אֵין־מַרְאֵ֙הוּ֙ עָמֹ֣ק מִן־הָע֔וֹר וְשֵׂעָ֥ר שָׁחֹ֖ר אֵ֣ין בּ֑וֹ וְהִסְגִּ֧יר הַכֹּהֵ֛ן אֶת־נֶ֥גַע הַנֶּ֖תֶק שִׁבְעַ֥ת יָמִֽים׃
And if the priest look on the plague of the scall, and, behold, the appearance thereof be not deeper than the skin, and there be no black hair in it, then the priest shall shut up him that hath the plague of the scall seven days.
Rashi on Leviticus
ושער שחור אין בו AND THERE IS NO BLACK HAIR IN IT [THE PRIEST SHALL SHUT HIM UP] — Consequently, if there is black hair in it, he is clean, and does not require to be shut up — for black hair is a characteristic of cleanness in cases of נתקים, as it is stated, (v. 37) “if there is black hair grown up in it … [he is clean]” (Sifra, Tazria Parashat Nega'im, Chapter 8 9).
Rashbam on Leviticus
ושער שחור אין בו והסגיר, if there had been black hair the person would be ritually completely pure and does not need to be isolated even for further examination purposes. This is spelled out clearly in verse 37.
Siftei Chakhamim
If there was a black hair in it, he is [ritually] clean. [Rashi explains this] so that you will not explain: “And behold! it does not appear deeper than the skin,” even if it has a black hair, and I might think that a black hair is a sign of impurity, or if it has no black hair, even if its appearance is deeper than the skin, it requires confinement, and the ו of ושער שחור is like או (or). Therefore, Rashi explains that everything depends on the black hair, as it says: “And a black hair [grew in it, the nesek is healed, he is clean].”