סימן צא סעיף יב
הַפּוֹתֵחַ מֻרְסָא כְּדֵי לְהַרְחִיב פִּי הַמַּכָּה, כְּדֶרֶךְ שֶׁהָרוֹפְאִים עוֹשִׂים, שֶׁהֵם מִתְכַּוְנִים לִרְפוּאָה לְהַרְחִיב פִּי הַמַּכָּה, הֲרֵי זֶה חַיָּב, שֶׁזּוֹ הִיא מְלֶאכֶת הָרוֹפֵא. וְאִם פְּתָחָהּ רַק כְּדֵי לְהוֹצִיא מִמֶּנָּהּ אֶת הַלֵּחָה שֶׁמְצַעַרְתּוֹ, וְאֵינוֹ חוֹשֵׁשׁ אִם תַּחֲזוֹר וְתִסָּתֵם מִיָּד, הֲרֵי זֶה מֻתָּר מִשּׁוּם צַעְרוֹ. וְדַוְקָא לְנָקְּבָהּ עַל יְדֵי מַחַט וְכַדּוֹמֶה אֲבָל לֹא בְצִפָּרְנָיו, מִשׁוּם דְּתוֹלֵשׁ קְצָת מֵעוֹר הַמֻּרְסָא, וְיֵש בָּזֶה חִיוּב. וְגַם עַל יְדֵי מַחַט וְכַדּוֹמֶה, כֵּיוָן שֶׁיֵּשׁ לָחוּשׁ, שֶׁמָּא יִתְכַּוֵּן שֶׁתִּשָׁאֵר פְּתוּחָה, כְּדֵי שֶׁתּוֹצִיא לֵחָה גַּם אַחַר כָּךְ עַל כֵּן אִם אֶפְשָׁר יֵשׁ לַעֲשׂוֹת עַל יְדֵי נָכְרִי.
One who punctures an abscess in order to enlarge the opening of the wound, in the manner of physicians when they attempt to facilitate healing by enlarging the opening of the wound,20This allows the abscess to drain and the wound to be exposed to the air which quickens the healing process. is guilty of a Shabbos violation,21He is liable for the melachah—מַכֶּה בְּפַּטִישׁ (lit. hammer—blow) i.e. the final act of a craftsman’s work, since this requires a degree of skill. [Shulchan Aruch 328: 28] Others hold him liable for the melachah—בּוֹנֶה (building). The creation of the opening is somewhat akin to building. [Rashi] for this requires a doctor's skill. If his [purpose in] opening it the abscess is only to drain the pus, which is causing him pain, and he is unconcerned if the [opening] closes up again immediately, this is permitted due to his pain.22This requires some clarification. The melachah of this paragraph (be it makeh bepatish or boneh, see footnote 21) requires that the wound be opened and remain open. Where the opening is not made for its own sake but only temporarily to drain the wound then it is “not a melachah for its own sake” i.e. a מְלָאכָה שֶׁאֵינָה צְרִיכָה לְגוּפָה, which according to all poskim except the Rambam is only d’rabanan and where pain is involved such an act is permitted.
The Rambam rules that מְלָאכָה שֶׁאֵינָה צְרִיכָה לְגוּפָה is d’oraisa. Nevertheless, he allows the temporary opening of a wound because in his opinion this cannot be construed as a melachah in any manner whatsoever. [Shaar Hatziyun 328: 65] [This is permitted] only when he punctures it with a needle or something similar.23Squeezing the wound is not permitted lest you cause bleeding. However, the blood already accumulated in the abscess may be cleaned out. [Mishnah Berurah 328: 89] But, [he may not do so] with his nails because he then tears some of the skin of the abscess, which makes him liable [for doing a melachah].24Others (Taz 328: 23 and Magein Avraham 301: 7) disagree and prefer using a fingernail to a needle in order to avoid the usual method of puncturing a wound provided care is taken not to tear any of the skin. [Biur Halachah] Even by means of a needle or something similar, there is concern that he may want the wound to remain open, so that the pus will continue to drain, therefore, wherever possible this should be done by a non-Jew.25Mishnah Berurah, ibid.
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.)