Engaging in Dangerous Activities
There is a mitzvah to take care of one's health and it is forbidden to put oneself in danger. The Torah instructs us several times to take heed to guard our souls. On this basis, some understand that this is why chazal warn us to be healthy. Additionally, there is a mitzvah to remove dangerous obstacles in your domain. And prohibition to to keep them in your domain.
- Most poskim hold that it is forbidden to smoke. 
- Aside from the issue of smoking in general, it is strictly forbidden to smoke in a shul. 
- It is absolutely forbidden to commit suicide and it is a very serious sin because Hashem didn't give us our bodies and lives to do with them whatever we like.
- It is forbidden to injure or cause a wound to oneself. If it is done for health purposes there is a discussion if it is permitted.
- It is absolutely forbidden to hit or injure someone else. In fact it is forbidden to insinuate that one is going to hit another Jew and one who does so is considered wicked.
- As explained earlier, it is absolutely forbidden to hit or injure someone else. There is a dispute whether one can allow someone else to injure oneself. A direct ramification of this dispute is whether it would be permitted to go paintballing knowing that it is very likely one will be injured but in advance agrees to it.
- Many poskim permit donating blood even though it involves inflicting a wound upon oneself. 
Piercings and Tattoos
- Regarding piercings and tattoos see the Tattoos_&_Body_Piercing page.
- Article on Living in Yesha during Dangerous Times by Rabbi Chaim Jachter
- Smoking and Halacha by Rabbi Yehuda Spitz
- Are Vaping and E-Cigarettes Kosher? - Rabbi Daniel Stein
- Devarim 4:9, 4:15
- Ketubot 30a, Levush YD 116
- Rambam Rotze'ach 11:4
- Rambam Rotze'ach 11:4
- Sh"t Tzitz Eliezer 17:21, Rav Chaim Kanievsky in Sheeilat Rav 1:52, Sh"t Teshuvot Vehanhagot 4:115, Rav Nisim Karelitz in a letter at the beginning of the book "Chaim Le-lo Ishun", Chacham Ovadia Yosef in Maran Peer Hador pg. 31, Teshuva of the RCA, Rabbi Chaim Jachter. See, however, Yechave Daat 5:39 and Igrot Moshe YD 2:49 regarding smoking.
- Yechave Daat 2:17, Yaskil Avdi 4:17:3, Ben Ish Chai Parashat Vayikra Halacha 5, Sh"t Maharshag 2:117, Kaf Hachaim 151:10
- The Midrash (Beresheet Rabba 34:5) learns from the pasuk that it is forbidden to commit suicide.
- Panim Yafot (Devarim 14:1) writes that it is forbidden to injure oneself based on Beresheet 9:1.
- Under certain circumstances, Igrot Moshe CM 2:65-66 permitted plastic surgery for aesthetic purposes.
- The pasuk (Devarim 25:3) warns against hitting a guilty sinner more than necessary. Chazal learn from here the general prohibition to hit any Jew, since if the Torah forbids hitting a sinner how much more so anyone else. This is considered a negative commandment by the Rambam (Lavin n. 300) and Sefer HaChinuch (n. 595).
- Chazal (Sanhedrin 58b) learn from Moshe that a Jew who raises his hand to hit another Jew is considered wicked. This is quoted by the Rambam (Sefer HaMitzvot lavin n. 300).
- Rabbi Yehuda Balsam outlines a dispute between the Minchat Chinuch and Turei Even who hold that it is permitted to allow someone else to injure oneself and Shulchan Aruch HaRav who forbids this. He writes that a practical application of this dispute is whether it is permitted to go paintballing.
- Igrot Moshe CM 1:103, Nishmat Avraham YD 349:3