Does the prohibition of Tzaar Baalei Chaim apply also against causing pain to humans, or being complicit to it? If one causes pain to another human does he transgress Tzaar Baalei Chaim?
Introduction: It is Biblically forbidden to cause pain to any living creature [without a Halachically justifiable reason]. The question is raised regarding if this Biblical prohibition likewise applies towards causing pain to humans. There are many matters that cause pain to another human which are already Biblically prohibited by the Torah, such as hitting, murder, stealing, Lashon Hara, embarrassing, teasing, and other forms of verbally induced pain, many of which are equally prohibited to be done both to a Jew or gentile. However, the question is asked regarding if there is also an additional prohibition of Tzaar Baalei Chaim to cause pain to another human, and whether one is required to do whatever he can to stop another person from being in pain due to the Mitzvah of Tzaar Baalei Chaim. Of the ramifications of this matter would be if one is obligated to do all that he can to prevent pain from occurring to another person, and if he must help them if he sees them in pain, such as carrying a heavy item. Likewise, may one cause pain to a child with playful intents, and may one tease him for playing purposes. How careful must parents be not to cause, physical, mental, or psychological pain to their children?
The law: Some Poskim rule that the Biblical prohibition of Tzaar Baalei Chaim applies only against causing pain to animals, and not to humans. Other Poskim, however, rule that the Biblical prohibition of Tzaar Baalei Chaim certainly applies likewise against causing pain to humans. This dispute however is limited to adults, however by children below the age of Mitzvos everyone agrees that there is a Biblical prohibition to cause them pain. Thus one must be very careful not to cause pain to children. [Accordingly, one should not tease a child even for playful purposes if it causes them pain or frustration. Likewise, for this reason one may not delay a child’s meal if they are hungry.] Furthermore, the above debate is only regarding whether the specific prohibition of Tzaar Baalei Chaim applies even against causing pain to a human, however everyone agrees that it is forbidden to do so, and one will be held accountable for any suffering that he causes another human being, whether physical or psychological.
 This would include all living creatures, even an insect.
Other opinions: Some Poskim rule the prohibition of Tzaar Baalei Chaim only applies to animals that perform productive work. [Sheilas Yaavetz 1:110]
 Admur Hilchos Ovrei Derachim 4; O.C. 266:25; Rama C.M. 272:9; Bava Metzia 32b
 See Rambam Sefer Hamitzvos Asei 203; Rashba 252; 256-257; Chinuch Mitzvah 80; 540-541; Smeh C.M. 272:13; Chavos Yair 191; Birkeiy Yosef Y.D. 372:2; Pela Yoeitz Erech Baalei Chaim; Minchas Elazar 4:61; Sdei Chemed Mareches Tzadi Kelal 3; Chazon Yechezkal Bava Metzia 1:12; Mateh Aaron 2; Yechaveh Daas 5:302
 Chavos Yair 191; See Minchas Elazar 4:61 in defense and explanation of the Chavos Yair; Radbaz 1:728 that there is no Mitzvah of Perika by a human
 The reason: As animals do not have Daas and are hence unable to accept the pain with love, in contrast to humans who have Daas and are hence able to ignore and overcome the pain. [Chavos Yair ibid]
 Birkeiy Yosef Y.D. 372:2 based on the following Poskim; Sheiris Yaakov [of Rav Yaakov Algazi] Parshas Tzav; Implication of Smeh C.M. 272:13 “The pain of a human is no less than that of an animal and it is a Kol Shekein”; Implication of Rashba ibid that the Mitzvah of Perika applies likewise to a human; Implication of Rambam Sefer Hamitzvos Asei 203 that the Mitzvah of Perika applies likewise to a human; Implication of Bava Metzia 31a “Tzaara Demara”; Sheiris Yaakov Tzav
 Pela Yoeitz ibid
 Pela Yoeitz ibid
 Pela Yoeitz ibid; See Chagiga 5a “On all the acts Hashem will bring to judgment, on all concealed matters, Shmuel says that this verse refers to one who spits in front of his friend and it became repulsive before him”