Commentary for Negaim 3:6
הַקָּרַחַת וְהַגַּבַּחַת מִטַּמְּאוֹת בִּשְׁנֵי שָׁבוּעוֹת, וּבִשְׁנֵי סִימָנִין, בְּמִחְיָה וּבְפִשְׂיוֹן. בְּמִחְיָה, בַּתְּחִלָּה, בְּסוֹף שָׁבוּעַ רִאשׁוֹן, בְּסוֹף שָׁבוּעַ שֵׁנִי, לְאַחַר הַפְּטוּר. וּבְפִסְיוֹן, בְּסוֹף שָׁבוּעַ רִאשׁוֹן, בְּסוֹף שָׁבוּעַ שֵׁנִי, וּלְאַחַר הַפְּטוּר. וּמִטַּמְּאוֹת בִּשְׁנֵי שָׁבוּעוֹת, שֶׁהֵן שְׁלשָׁה עָשָׂר יוֹם:
Posterior baldness or frontal baldness are made impure after two weeks or through two signs: a healed patch [of skin], or expansion. Regarding a healed patch, [it is made impure] initially, after the first week [of quarantine], after the second week [or] after the exemption. And regarding expansion, after the first week, after the second week, [or] after the exemption. And they are made impure after two weeks [maximum], which are [actually] thirteen days.
Bartenura on Mishnah Negaim
English Explanation of Mishnah Negaim
"By quick flesh," in the beginning, at the end of the first week, at the end of the second week, or after they have been pronounced clean.
"Or by a spreading," at the end of the first week, at the end of the second week, or after they have been pronounced clean.
They become unclean for two weeks which are only thirteen days.
Section one: Today's mishnah outlines the signs and length of impurity for negaim that appear on a bald head or a scalp (Leviticus 13:40).
The remainder of this mishnah has already been explained above in mishnayot 2-5.