The Rabbinic decree on the stain (כתם דרבנן as against the הרגשה דאורייתא), the שיעור כגריס ועוד, the place and shape of the stain, an object that cannot receive impurity, the תליות (wound, external blood, insects), and the great heter of the בגדי צבעונים (Shulchan Arukh, Yoreh De'ah 190 — 54 seifim)
דְּבַר תּוֹרָה אֵין הָאִשָּׁה מִטַּמְּאָה וְלֹא אֲסוּרָה לְבַעְלָהּ עַד שֶׁתַּרְגִּישׁ שֶׁיָּצָא דָם מִבְּשָׂרָהּ; וַחֲכָמִים גָּזְרוּ עַל כֶּתֶם שֶׁנִּמְצָא בְּגוּפָהּ אוֹ בִּבְגָדֶיהָ שֶׁהִיא טְמֵאָה וַאֲסוּרָה לְבַעְלָהּ אַף עַל פִּי שֶׁלֹּא הִרְגִּישָׁה.
By Torah law a woman is neither impure nor forbidden to her husband until she has felt (הרגשה) that blood emerged from her body; but the Sages decreed on the stain (כתם) found on her body or her garments that she is impure and forbidden to her husband, even though she felt nothing.
Shulchan Arukh, Yoreh De'ah 190:1LEVEL 01
The Hebrew text of the 54 seifim with fluent English translation. The Rabbinic decree on the stain (דרבנן as against the הרגשה דאורייתא), the שיעור כגריס ועוד, the place of the stain (כנגד בית התורפה), an object that cannot receive impurity, the תליות and the heter of the בגדי צבעונים, explained with practical cases (colored undergarments, showing the stain to a Rav).
📖 StudyLEVEL 02
In-depth pilpul: the nature of the decree (כתם דרבנן vs הרגשה דאורייתא, linked to siman 183), the logic of the שיעור כגריס ועוד (the attribution to the כינה) and the non-combination of drops, the hierarchy of the תליות (מכה / external blood / כינה / צבעונים), the source of the heter of the צבעונים (לא גזרו אלא בלבן), and the דבר שאינו מקבל טומאה (Taz greatly developed, חקירות and נפקא מינות).
📖 StudyLEVEL 03
Comparative tables (כגריס or less, white / צבעוני, מקבל טומאה or not, the types of תליות), golden rules, classic pitfalls (combining drops, place of the stain, color of the external cause) and memorization of the 9 families covering the 54 seifim.
📖 StudyLEVEL 04
The shitah of the Tzemach Tzedek of Lubavitch and the Chabad mesorah on stains and the heter of the צבעונים, then the halacha lema'asse according to the Beit Yossef, the Rama, the Shach, the Taz, the Sidrei Tahara, the Chochmat Adam, the Aroukh haShulchan and contemporary pesak (Taharat haBayit, Shevet haLevi). Since stains are דרבנן, practice holds many leniencies — but applying them requires a Rav.
📖 StudyA כתם is a bloodstain found on a woman's body or her garments without her having felt anything. By Torah law a woman is a נדה only if she has an הרגשה — the sensation that blood emerged from her body (דבר תורה אין האשה מטמאה עד שתרגיש שיצא דם מבשרה — YD 190:1). A stain found without הרגשה is therefore not a Torah impurity; it is the Sages who decreed (וחכמים גזרו על כתם) that it renders her טמאה ואסורה לבעלה. Because this impurity is דרבנן, the siman holds many leniencies (תליות, measure, place, colors): ספקא דרבנן לקולא. But applying them requires a Rav.
The Sages decreed on a stain only if it reaches the measure of a kidney-bean and a bit more (כגריס ועוד — YD 190:5). The measure of the גריס is that of nine lentils arranged in a 3×3 square. Below it she is טהורה, for the small stain is attributed to a crushed insect (כינה / מאכולת). One does not combine several separate small drops (190:8): each drop is attributed to a distinct insect so long as none alone reaches כגריס ועוד in one place. The exact calculation of the measure requires a Rav.
Since stains are דרבנן, we are lenient and attribute the stain to any possible cause (כיון שכתמים דרבנן מקילין בהם ותולה בכל דבר שיכולה לתלות — YD 190:18). One may thus attribute the stain to a wound (מכה) from which the blood could have come (190:16), to external blood — having passed through the butchers' market, handled a bird or a slaughtered animal (190:18, cf. siman 185) — or to insects: louse, bedbug (כינה, פשפש), up to the measure of the turmus (190:7). These תליות are governed by precise conditions (color, place, measure): never rule alone, consult your Rav.
The Sages decreed on a כתם only when it is found on white; a stain found on a colored garment (צבעוני) does not render the woman טמאה. Hence the widespread practice, already mentioned by the Rishonim and codified by the Rama, of wearing colored undergarments (בגדי צבעונים) to avoid most of the problems of stains. This is the most important practical leniency of the siman today. Its conditions (when it applies, its limits during the שבעה נקיים) are the province of the Rav.