סימן קסא סעיף ח
בְּצוֹאָה שֶׁתַּחַת הַצִּפֹּרֶן, יֵשׁ חִלּוּקִים. וּכְבָר נָהֲגוּ לַחְתֹּךְ צִפָּרְנֵי יְדֵיהֶן וְרַגְלֵיהֶן קֹדֶם הַטְּבִילָה. וְתִזָּהֵר לְשָׂרְפָן, כִּי אִם יִדְרֹךְ עֲלֵיהֶן בַּעְלָהּ אוֹ אָדָם אַחֵר, מְסֻכָּן. וּבְשַׁבָּת וְיוֹם טוֹב אִם שָׁכְחָה לְחָתְכָן קֹדֶם, יֵשׁ מַתִּירִין לְחָתְכָן עַל יְדֵי גוֹיָה. אִם יֵשׁ לָה נֶפַח עַל מְקוֹם הַצִּפֹּרֶן, וְאֵינָהּ יְכוֹלָה לֹא לְחָתְכוֹ וְלֹא לְנַקֵּר תַּחְתָּיו, אִם נָפוּחַ כָּל כָּךְ שֶׁאֵין הַטִּיט שֶׁתַּחְתָּיו נִרְאֶה, אֵינוֹ חוֹצֵץ. אִשָּׁה שֶׁשָּׁכְחָה לַחְתֹּךְ צִפֹּרֶן וְטָבְלָה כָּךְ, אִם נִזְכְּרָה קֹדֶם שֶׁנִּזְקְקָה לְבַעְלָהּ, צְרִיכָה טְבִילָה אַחֶרֶת. וְאִם לֹא נִזְכְּרָה עַד לְאַחַר שֶׁנִּזְקְקָּה לְבַעְלָהּ, תַּעֲשָׂה שְׁאֵלַת חָכָם.
Concerning dirt under the nails, there are a number of factors involved. It is already the established custom to cut the nails of the hands and the feet before the ritual immersion. She must be careful to burn them afterward, for if her husband should step on them, or if another man should step on them it is dangerous. (When she immerses) on Shabbos or Yom Tov, and has forgotten to cut them beforehand, some authorities permit her to have them cut4Taz 198:21 forbids this and says she should immerse without having them cut, but should clean under them. Biur Halacha 340: 1 rules like Magein Avrohom, Nekudos Hakessef, and Shevus Yaakov Vol. 2 Responsa 8 that if need be she may have a non-Jewess cut them even with a clipper. The Chacham Tzvi does not permit having them cut with a tool. Toe nails should just be cleaned, rather than cut by a non-Jewess on Shabbos. (Biur Halachah) (on Shabbos) by a non-Jewess. If she has a swelling over the nail, and is thus unable to cut it or to clean underneath it, and the swelling is so large that the dirt underneath it is not visible, it is not a chatsitsah. If a woman forgot to cut her nails and performed the ritual immersion, and became aware of it before having marital relations with her husband, she must have another immersion. If she did not become aware of it until after having marital relations with her husband, she should consult a Rav.
תנא דבי אליהו כל השונה הלכות בכל יום מובטח לו שהוא בן העולם הבא שנאמר הליכות עולם לו אל תקרי הליכות אלא הלכות (נדה ע"ג.)