Halacha

הלכה א
הַפִּשְׂיוֹן מְטַמֵּא בְּכָל שֶׁהוּא וְהוּא שֶׁיִּהְיֶה הַפִּשְׂיוֹן מֵאַחַת מִמַּרְאוֹת הַנְּגָעִים. אֲבָל אִם הָיָה הַפִּשְׂיוֹן מַרְאֵה בֹּהַק אֵינוֹ פִּשְׂיוֹן. וְאֵין הַפִּשְׂיוֹן סִימַן טֻמְאָה עַד שֶׁיִּפְשֶׂה חוּץ לַנֶּגַע אֲבָל אִם פָּשָׂה לְתוֹךְ הַנֶּגַע הֲרֵי הוּא כְּמוֹת שֶׁהָיָה. כֵּיצַד. בַּהֶרֶת וּבְתוֹכָהּ בָּשָׂר חַי פָּחוֹת מִכַּעֲדָשָׁה וְהִסְגִּירָהּ וּבְסוֹף הַשָּׁבוּעַ נִתְמַעֲטָה הַמִּחְיָה מִמַּה שֶּׁהָיְתָה אוֹ שֶׁהָלַךְ הַבָּשָׂר הַחַי כֻּלּוֹ אֵין זֶה פִּשְׂיוֹן. שֶׁאֵין הַבַּהֶרֶת פּוֹשָׂה לְתוֹכָהּ אֶלָּא חוּצָה לָהּ:
כסף משנה
1.
The increase of a blemish imparts impurity regardless of its size, provided the increase was one of the shades of blemishes that impart impurity. If, however, the increase was the color of a bohak, it is not considered as an increase. An increase of a blemish is a sign of impurity only when it spreads beyond the blemish. If, however, it spreads within the blemish, the person's original status is unchanged.
What is implied? There was a baheret with less than a lentil of healthy flesh inside of it. He was therefore isolated. At the end of a week, if the size of the healthy flesh was diminished or it disappeared entirely, it is not considered as an increase. For, to be significant, an increase of a baheret may not spread within its own midst, but rather outside of it.

הלכה ב
אֵין הַפִּשְׂיוֹן סִימַן טֻמְאָה עַד שֶׁיִּהְיֶה אַחַר הֶסְגֵּר. אֲבָל אִם בָּא בַּתְּחִלָּה וְרָאָה הַכֹּהֵן אֶת הַנֶּגַע שֶׁהוּא פּוֹשֶׂה וְהוֹלֵךְ אֵינוֹ מַחְלִיטוֹ אֶלָּא מַסְגִּירוֹ עַד סוֹף הַשָּׁבוּעַ וְיֵרָאֶה:
כסף משנה
2.
An increase is not considered as a sign of impurity unless it comes after isolation. If, however, a person came at the outset and the priest saw the blemish increasing, he does not deem the person definitively impure. Instead, he isolates him until the end of the week and then observes it.

הלכה ג
אֵין הַבַּהֶרֶת פּוֹשָׂה לְתוֹךְ הַשְּׁחִין וְלֹא לְתוֹךְ הַמִּכְוָה. וְלֹא לְתוֹךְ מִחְיַת הַשְּׁחִין וְלֹא לְתוֹךְ מִחְיַת הַמִּכְוָה. וְלֹא לָרֹאשׁ וְלֹא לַזָּקָן אַף עַל פִּי שֶׁנִּקְרְחוּ וְהָלַךְ הַשֵּׂעָר מֵהֶן שֶׁנֶּאֱמַר (ויקרא יג ז) "וְאִם פָּשֹׂה תִפְשֶׂה הַמִּסְפַּחַת בָּעוֹר". אֲבָל בַּהֶרֶת שֶׁפָּשְׂתָה לְתוֹךְ הַבֹּהַק הֲרֵי זֶה פִּשְׂיוֹן:
כסף משנה
3.
To be significant, an increase may not spread into a boil or into burnt flesh or into a healed boil or burn, nor on the head, nor on the beard even though they became bald and the hair was removed from them, as implied by Leviticus 13:7: "If the blemish will spread on the skin." If, however, a baheret spreads to a bohak, it is considered an increase.

הלכה ד
הַשְּׁחִין וְהַמִּכְוָה וְהַבֹּהַק וּמִחְיַת הַשְּׁחִין וּמִחְיַת הַמִּכְוָה שֶׁהֵן חוֹלְקִין בֵּין הָאוֹם לַפִּשְׂיוֹן אֵינוֹ סִימַן טֻמְאָה. הִסְגִּירוֹ וְהָלְכוּ לָהֶן עַד שֶׁנִּמְצָא הַפִּשְׂיוֹן סָמוּךְ לָאוֹם הֲרֵי זֶה מֻחְלָט:
כסף משנה
4.
If a boil, burnt flesh, a bohak, or a healed boil or burn separate between an increase and the original blemish, it is not a sign of impurity. If the person was isolated and these skin conditions departed and this increase was immediately adjacent to the original blemish, he is deemed definitively impure.

הלכה ה
בַּהֶרֶת כִּגְרִיס וּפָשְׂתָה כַּחֲצִי גְּרִיס וְעוֹד וְהָלַךְ מִן הָאוֹם כַּחֲצִי גְּרִיס. אַף עַל פִּי שֶׁהַנּוֹתָר מִן הָאוֹם עִם הַפִּשְׂיוֹן יֶתֶר מִכִּגְרִיס [הֲרֵי] זֶה טָהוֹר. הָיְתָה כִּגְרִיס וּפָשְׂתָה כִּגְרִיס וְעוֹד וְהָלְכָה לָהּ הָאוֹם תֵּרָאֶה בַּתְּחִלָּה וְיַסְגִּיר שָׁבוּעַ אַחַר שָׁבוּעַ. הָיְתָה בּוֹ בַּהֶרֶת וְהִסְגִּירוֹ וְהָלְכָה הַבַּהֶרֶת בְּסוֹף יְמֵי הֶסְגֵּר וְחָזְרָה בַּהֶרֶת בִּמְקוֹמָהּ כְּמוֹת שֶׁהָיְתָה הֲרֵי הוּא כְּמוֹ שֶׁהָיָה. נִתְמַעֲטָה [בְּתוֹךְ יְמֵי הֶסְגֵּר] וּפָשְׂתָה וְחָזְרָה כְּמוֹת שֶׁהָיְתָה אוֹ שֶׁפָּשְׂתָה וְנִתְמַעֵט הַפִּשְׂיוֹן וְחָזְרָה כְּמוֹת שֶׁהָיְתָה הֲרֵי זֶה יַסְגִּיר אוֹ יִפְטֹר:
כסף משנה
5.
When there was a baheret the size of a gris and it spread more than a half a gris, but approximately half a gris of the original blemish disappeared, the person is pure even though together, there remained more than a gris from the original blemish and the increase.
If the original blemish was the size of a gris and it spread more than a gris, but the original blemish disappeared entirely, it should be given an initial observation and isolated week after week. If a person has a baheret and was isolated and the baheret disappeared at the end of the days of isolation, and then the baheret returned to its original place, it is given its initial status. If it became diminished during the days of his isolation and then expanded and returned to its original size at the end of the week or increased and then the increased blemish diminished and returned to its original size at the end of the week, he should continue in isolation or is released from the process of inspection.

הלכה ו
בַּהֶרֶת כִּגְרִיס וּפָשְׂתָה כִּגְרִיס וְנוֹלַד בַּפִּשְׂיוֹן מִחְיָה אוֹ שֵׂעָר לָבָן וְהָלְכָה לָהּ הָאוֹם תֵּרָאֶה בַּתְּחִלָּה. הָיְתָה בּוֹ בַּהֶרֶת כִּגְרִיס וְהִסְגִּירוֹ. בְּסוֹף הַשָּׁבוּעַ וַהֲרֵי הִיא כְּסֶלַע, סָפֵק שֶׁהִיא הִיא סָפֵק שֶׁהִיא אַחֶרֶת, בָּאָה תַּחְתֶּיהָ הֲרֵי זֶה טָמֵא:
כסף משנה
6.
If a baheret was the size of a gris, it then increased the size of a gris, then healthy flesh or white hair erupted in it, and then the original blemish disappeared, it should be given an initial observation.
The following rules apply if a person had a baheret the size of a gris and he was isolated. At the end of the week, the blemish was the size of a sela, but there was a doubt whether it was the original blemish or a new one that came in its place, it is impure.

הלכה ז
בַּהֶרֶת כִּגְרִיס וְחוּט יוֹצֵא מִמֶּנּוּ אִם יֵשׁ בּוֹ רֹחַב שְׁתֵּי שְׂעָרוֹת זוֹקְקָהּ לְשֵׂעָר לָבָן וּלְפִשְׂיוֹן אֲבָל לֹא לְמִחְיָה שֶׁאֵין הַמִּחְיָה סִימַן טֻמְאָה עַד שֶׁתַּקִּיף אוֹתָהּ הַבַּהֶרֶת וְיִהְיֶה בֵּין סוֹף הַמִּחְיָה וְסוֹף הַבַּהֶרֶת רֹחַב צְמִיחַת שְׁתֵּי שְׂעָרוֹת. הָיוּ שְׁתֵּי בֶּהָרוֹת וְחוּט יוֹצֵא מִזּוֹ לָזוֹ אִם יֵשׁ בּוֹ רֹחַב שְׁתֵּי שְׂעָרוֹת מְצָרְפָן וְאִם לָאו אֵינוֹ מְצָרְפָן. הִסְגִּירוֹ שָׁבוּעַ אַחַר שָׁבוּעַ וְלֹא נוֹלַד לוֹ סִימַן טֻמְאָה וּפְטָרוֹ וּלְאַחַר הַפִּטּוּר פָּשָׂה הַנֶּגַע כָּל שֶׁהוּ הֲרֵי זֶה מֻחְלָט:
כסף משנה
7.
The following rules apply when there is a baheret more than the size of a gris and a stretch of afflicted flesh emerging from it. If the stretch is two hairs wide, it requires white hair or an increase in size for the person to be considered impure. If, however, healthy flesh appears in it, this ruling does not apply. The rationale is that healthy flesh is not considered as a sign of impurity unless it is surrounded by a baheret and there is a space where two hairs can grow between the edge of the healthy flesh and the edge of the baheret.
The following laws apply when there were two baharot and a stretch of afflicted flesh extending from one to the other. If it is two hairsbreadth wide, they are considered as being joined together. If not, they are not considered as joined.
When the afflicted person was isolated as a result of a blemish for one week after another and a sign of impurity did not appear and, as a result, he was released from the process of inspection, but after he was released from the process of inspection, the blemish increased in size even slightly, he should be deemed definitively impure.

הלכה ח
בַּהֶרֶת שֶׁטָּהֲרָה מִתּוֹךְ הֶסְגֵּר אוֹ מִתּוֹךְ הֶחְלֵט שֶׁהָלְכוּ מִמֶּנָּה סִימָנֵי טֻמְאָה אֵין מַסְגִּירִין בָּהּ לְעוֹלָם:
כסף משנה
8.
When a baheret was declared pure either after the afflicted person was isolated or deemed definitively impure, i.e., the signs of impurity disappeared, he should not be isolated again.

הלכה ט
בַּהֶרֶת שֶׁכָּנְסָה אַחַר הַפִּטּוּר וּפָשְׂתָה לִכְמוֹת שֶׁהָיְתָה אוֹ שֶׁפָּשְׂתָה וְחָזְרָה לִכְמוֹת שֶׁהָיְתָה הֲרֵי הוּא בְּטָהֳרָתוֹ:
כסף משנה
9.
When a baheret diminished after the person was released from the process of inspection after isolation and then increased to its original size or it increased and then decreased to its original size, the person remains in his state of purity.

הלכה י
בַּהֶרֶת כִּגְרִיס וּבָהּ מִחְיָה כַּעֲדָשָׁה וְשֵׂעָר לָבָן בְּתוֹךְ הַמִּחְיָה וְהֶחְלִיטוֹ וּלְאַחַר הֶחְלֵט הָלְכָה הַמִּחְיָה טָמֵא מִפְּנֵי שֵׂעָר לָבָן. הָלַךְ הַשֵּׂעָר לָבָן טָמֵא מִפְּנֵי הַמִּחְיָה. הָיָה הַשֵּׂעָר לָבָן בְּתוֹךְ הַבַּהֶרֶת וְהָלָךְ לוֹ טָמֵא מִפְּנֵי הַמִּחְיָה. הָלְכָה הַמִּחְיָה טָמֵא מִפְּנֵי שֵׂעָר לָבָן:
כסף משנה
10.
The following laws apply when there is a baheret the size of a gris and healthy flesh the size of a lentil in it and white hair in the midst of the healthy flesh. The afflicted person was deemed definitively impure. After that determination was made, the healthy flesh disappeared. He is still impure because of the white hair. If the white hair disappeared, he is impure because of the healthy flesh.
If the white hair was located in the baheret and not in the healthy flesh and then the white hair disappeared, the afflicted person is impure because of the healthy flesh. If the healthy flesh disappeared, he is still impure because of the white hair.

הלכה יא
בַּהֶרֶת וּבָהּ מִחְיָה וּפִשְׂיוֹן. הָלְכָה הַמִּחְיָה טָמֵא מִפְּנֵי הַפִּשְׂיוֹן. הָלַךְ הַפִּשְׂיוֹן טָמֵא מִפְּנֵי הַמִּחְיָה. וְכֵן בְּשֵׂעָר לָבָן וּבְפִשְׂיוֹן. הֶחְלִיטוֹ בְּשֵׂעָר לָבָן וְהָלַךְ הַשֵּׂעָר וְחָזַר בּוֹ שֵׂעָר לָבָן אַחֵר. אוֹ שֶׁנּוֹלְדָה לוֹ מִחְיָה אוֹ פִּשְׂיוֹן. אוֹ שֶׁהֶחְלִיטוֹ בְּמִחְיָה וְהָלְכָה הַמִּחְיָה וְנוֹלְדָה לוֹ מִחְיָה אַחֶרֶת. אוֹ שֵׂעָר לָבָן אוֹ פִּשְׂיוֹן. אוֹ שֶׁהֶחְלִיטוֹ בְּפִשְׂיוֹן וְהָלַךְ הַפִּשְׂיוֹן וְחָזַר בּוֹ פִּשְׂיוֹן אַחֵר. אוֹ שֶׁנּוֹלְדָה בָּהּ מִחְיָה אוֹ שֵׂעָר לָבָן. הֲרֵי זֶה בְּטֻמְאָתוֹ כְּמוֹת שֶׁהָיָה. אֶחָד הַטָּמֵא שֶׁהֻחְלַט בַּתְּחִלָּה אוֹ שֶׁהֻחְלַט בְּסוֹף שָׁבוּעַ רִאשׁוֹן אוֹ בְּסוֹף שָׁבוּעַ שֵׁנִי אוֹ אַחַר הַפִּטּוּר. הוֹאִיל וְהֻחְלַט מִכָּל מָקוֹם אֵינוֹ טָהוֹר עַד שֶׁלֹּא יִשָּׁאֵר בּוֹ סִימַן טֻמְאָה לֹא סִימַן הֶחְלֵט וְלֹא סִימָן אַחֵר:
כסף משנה
11.
The following rules apply when after a person with a baheret was isolated for a week, he was deemed impure, because there was healthy flesh in the baheret and it increased in size. If later the healthy flesh disappeared, he is impure because of the increase. If the increase disappeared, he is impure because of the healthy flesh.
If a person was deemed definitively impure because of white hair, that white hair disappeared, but other white hair appeared, healthy flesh appeared, or the size of the blemish increased, his status of impurity remains unchanged. This law also applies if a person was deemed definitively impure because of healthy flesh and the healthy flesh disappeared, but other healthy flesh or white hair appeared or the size of the blemish increased or he was deemed definitively impure because the size of the blemish increased, that increase disappeared, but there was another increase or healthy flesh or white hair appeared.
Whether an afflicted person was deemed impure when he originally appeared before the priest, at the end of the first week of isolation, at the end of the second week, or after he was released from the process of inspection, since he was deemed definitively impure in any instance, he is not pure until no sign of impurity remains upon him, neither the sign for which he was deemed impure or any other sign.

טהרה הלכות טומאת צרעת פרק ד
Taharah Tumas Tzara’as Chapter 4