Commentary for Negaim 1:6
כֵּיצַד לְהַחְמִיר. לֹא הָיָה בוֹ שֵׂעָר לָבָן וְנוֹלַד לוֹ שֵׂעָר לָבָן, הָיוּ שְׁחוֹרוֹת וְהִלְבִּינוּ, אַחַת שְׁחוֹרָה וְאַחַת לְבָנָה וְהִלְבִּינוּ שְׁתֵּיהֶן, קְצָרוֹת וְהֶאֱרִיכוּ, אַחַת קְצָרָה וְאַחַת אֲרֻכָּה וְהֶאֱרִיכוּ שְׁתֵּיהֶן, נִסְמַךְ הַשְּׁחִין לִשְׁתֵּיהֶן אוֹ לְאַחַת מֵהֶן, הִקִּיף הַשְּׁחִין אֶת שְׁתֵּיהֶן אוֹ אֶת אַחַת מֵהֶן, אוֹ חִלְּקוֹ הַשְּׁחִין וּמִחְיַת הַשְּׁחִין וְהַמִּכְוָה וּמִחְיַת הַמִּכְוָה וְהַבֹּהַק וְהָלְכוּ לָהֶם, לֹא הָיְתָה בוֹ מִחְיָה וְנוֹלְדָה לוֹ מִחְיָה, הָיְתָה עֲגֻלָּה אוֹ אֲרֻכָּה וְנַעֲשֵׂית מְרֻבַּעַת, מִן הַצַּד וְנַעֲשֵׂית מְבֻצֶּרֶת, מְפֻזֶּרֶת וְנִתְכַּנְּסָה וּבָא הַשְּׁחִין וְנִכְנַס בְּתוֹכָהּ, הִקִּיפָהּ, חִלְּקָהּ, אוֹ מִעֲטָהּ הַשְּׁחִין אוֹ מִחְיַת הַשְּׁחִין וְהַמִּכְוָה וּמִחְיַת הַמִּכְוָה וְהַבֹּהַק וְהָלְכוּ לָהֶן, לֹא הָיָה בוֹ פִסְיוֹן וְנוֹלַד בּוֹ פִסְיוֹן, הַשְּׁחִין וּמִחְיַת הַשְּׁחִין וְהַמִּכְוָה וּמִחְיַת הַמִּכְוָה וְהַבֹּהַק חוֹלְקִין בֵּין הָאוֹם לַפִּסְיוֹן וְהָלְכוּ לָהֶן, הֲרֵי אֵלּוּ לְהַחְמִיר:
How [is waiting until after Shabbat considered] a stringency? [If] he did not have in [the <i>Nega</i>] white hair [on Shabbat] and [after Shabbat] white hair grew in it, [or if] there were black [hairs] and they whitened, [or if] one was black and one was white and the two of them whitened, [or if the hairs were] short and they were lengthened, [or if there were] one long and one short, and the two of them were lengthened, [or if on Shabbat] a boil encroached upon the two of them or upon one of them, [or if] a boil surrounded the two of them or one of them, or divided them - [this refers to] a boil, a partly-healed boil, a burn, a partly-healed burn, or a <i>Bohak</i> - and went away [after Shabbat]. [Other cases of leniency include if the skin] did not have a healed part and then grew a healed part, [or if the area of the <i>Nega</i>] was circular or stretched and became square, [or if a healed part of skin] had from the side [a <i>Nega</i>] and then became surrounded, [or if the healed part of skin] was scattered and then became concentrated, [or if] a boil came and went into [the healed part of the skin], surrounded it, split it, or diminished it - [this refers to] a boil, a partly-healed boil, a burn, a partly-healed burn, or a <i>Bohak</i> - and went away [after Shabbat], [or if the <i>Nega</i>] did not have an extension and then grew an extension, [or if a] boil, a partly-healed boil, a burn, a partly-healed burn, or a <i>Bohak</i> separate between the original and its expansion and went away [after Shabbat]. These are [cases in which waiting until after Shabbat is considered a] stringency.
Bartenura on Mishnah Negaim
English Explanation of Mishnah Negaim
If it had no white hairs and then white hairs appeared; If they were black and then turned white; If one hair was black and the other white and both turned white; If they were short and they became long; If one was short and the other long and both became long.
If a boil adjoined both hairs or one of them, if a boil encompassed both hairs or one of them or if they were parted from one another by a boil, the quick flesh of a boil, a burn, or the quick flesh of a burn, or white scurf, and then [one of these things] disappeared.
If it had no quick flesh and then quick flesh appeared.
If it was round or long and then became four sided; If it was at the side and then it became encompassed. If it was dispersed and then it became united or a boil appeared and made its way into it. If it was encompassed, parted or lessened by a boil, the quick flesh of a boil, a burn, the quick flesh of a burn or white scurf, and then they disappeared;
If it had no spreading and then a spreading appeared;
If a boil, the quick flesh of a boil, a burn, the quick flesh of a burn, or white scurf formed a division between the first sign and the spreading and then they disappeared. Behold all of these lead to a stringency.
Today's mishnah is basically the opposite of yesterday's. It deals with scenarios in which the nega was pure on Shabbat, but then by Sunday, when it was examined it had become impure. We shall explain how this leads to a stringency.
Section one: On Shabbat there were no white hairs in the nega but since there were white hairs by the time he saw him after Shabbat, he is impure. This creates a stringency.
We should note that had the priest seen him on Shabbat, he would have put him into isolation and then when the white hairs appeared (or any other case mentioned below), he would have had to declare him impure. Therefore, we might ask why this is considered a stringency. The answer is that the extra week might have afforded him time to heal, and by the time the priest saw him a second time, he may have healed and never became impure.
The rest of the mishnah is just a reversal of the order found in yesterday's mishnah. To understand what is going on, refer back there. I will make a few comments that will help here.
Section two: On Shabbat there were signs that would prevent the nega from being impure. However, by the time Sunday rolled around those signs were gone. Similarly, in the cases below, the mitigating signs disappear right after Shabbat, before he is examined.
Section three: The quick flesh causes it to be impure.
Sections 4-6: See yesterday's mishnah.