(א) אָסוּר לְאָדָם לַחֲבל בֵּין בְּעַצְמוֹ בֵּין בַּחֲבֵרוֹ. וְלֹא הַחוֹבֵל בִּלְבַד אֶלָּא כָּל הַמַּכֶּה אָדָם כָּשֵׁר מִיִּשְׂרָאֵל בֵּין קָטָן בֵּין גָּדוֹל בֵּין אִישׁ בֵּין אִשָּׁה דֶּרֶךְ נִצָּיוֹן הֲרֵי זֶה עוֹבֵר בְּלֹא תַּעֲשֶׂה שֶׁנֶּאֱמַר (דברים כה ג) "לֹא יֹסִיף" (דברים כה ג) "לְהַכֹּתוֹ". אִם הִזְהִירָה תּוֹרָה מִלְּהוֹסִיף בְּהַכָּאַת הַחוֹטֵא קַל וָחֹמֶר לְמַכֶּה אֶת הַצַּדִּיק:
(1) A man is forbidden to injure himself or another. Not only one who inflicts a wound, but anyone who strikes a worthy Jew, whether an adult or a minor, whether a man or a woman, (in a degrading/belligerent manner) breaks a prohibitive law, as it is written: "He must not lash him excessively" (Deuteronomy 25:3). If the Torah has warned against excess in lashing an offender, how much more should this apply to striking an innocent man.
סבר לה כי הא דתניא מגרר אדם גלדי צואה וגלדי מכה שעל בשרו בשביל צערו, אם בשביל ליפות אסור
Mar Zutra holds in accordance with that which was taught in a baraita: A person may scrape off dried excrement crusts and scabs of a wound that are on his flesh because of the pain that they are causing him. However, if he does so in order to clean and beautify himself, it is prohibited.
בשביל צערו - ואם אין לו צער אחר אלא שמתבייש לילך בין בני אדם שרי דאין לך צער גדול מזה:
Because of his pain: And if there is no other pain than the fact that he is embarrassed to walk amongst others, it is permitted, because there is no greater pain than this.
(ג) הָיָה קוֹץ תָּחוּב לְאָבִיו, לֹא יוֹצִיאֶנּוּ, שֶׁמָּא יָבֹא לַעֲשׂוֹת בּוֹ חַבּוּרָה. וְכֵן אִם הוּא מַקִּיז דָּם, אוֹ רוֹפֵא, לֹא יַקִּיז דָּם לְאָבִיו וְלֹא יַחְתֹּךְ לוֹ אֵבֶר, אַף עַל פִּי שֶׁמְּכַוֵּן לִרְפוּאָה. הַגָּה: בַּמֶּה דְּבָרִים אֲמוּרִים, בְּשֶׁיֵּשׁ שָׁם אַחֵר לַעֲשׂוֹת. אֲבָל אִם אֵין שָׁם אַחֵר לַעֲשׂוֹת וְהוּא מִצְטַעֵר, הֲרֵי הוּא מַקִּיזוֹ וְחוֹתֵךְ לוֹ כְּפִי מַה שֶּׁיַּרְשׁוּהוּ לַעֲשׂוֹת. (גַּם זֶה בַּטּוּר ורמב''ם פ''ב מַמְרִים).
(3) If his father has a thorn stuck (in his skin, needing removal), he should not remove it, perhaps he (the son) will wound him, and similarly, if he is a blood-letter or doctor, he should not let blood for his father, and should not cut off a limb, even though he intends to do this for medical reasons. Rama - When do this apply, when this is no one else to do it, but if there is no one else, and the father is in pain, he may let blood or cut off the limb, as long as he (the father) allows him.
The Avnei Nezer had forbidden a child to have surgery to straighten a crooked leg due to the risk of the operation.
Rabbi Waldenberg objects to performing surgery on someone who is neither sick nor in pain. He argues that such activities are outside the boundaries of the physician's mandate to heal (since he questions whether cosmetic surgery is truly included in the category of healing). He further asserts that the patient has no right to ask the physician to wound him or her for the purposes of merely enhancing beauty. Rabbi Waldenberg then makes the theological argument that as the ultimate artisan, G-d creates each person in His image, exactly as he or she should be, with nothing extra nor anything lacking. He therefore posits that cosmetic surgery that is not for pain or true illness is an affront to G-d and is forbidden.
Rav Ḥisda, when he would walk among thorns and shrubs, would raise his clothing despite the fact that his skin would get scratched by the thorns. He said in explanation of his actions: This flesh will heal if scratched, but that garment will not heal if torn.
ת"ר יין תוסס אין בו משום גילוי ... כמאן כי האי תנא דתניא רבי אליעזר אומר אוכל אדם ענבים ותאנים בלילה ואינו חושש משום שנאמר (תהלים קטז, ו) שומר פתאים ה.
§ The Gemara discusses the halakha of exposure with regard to various foods and beverages. The Sages taught: Wine that is still fermenting is not subject to the halakha of exposure. ... In accordance with whose opinion is this stated? It is stated in accordance with the opinion of this tanna, as it is taught in a baraita that Rabbi Eliezer said: A person may eat grapes and figs at night, and he need not have cause for concern, as it is stated: “The L-rd preserves the simple” (Psalms 116:6).
“And shall cause him to be thoroughly healed” (Exodus 21:19), from here we derive that permission is granted to a doctor to heal. The practice of medicine is in accordance with the will of G-d.