Must one wash his hands after cutting facial hair such as the mustache?
According to many Poskim[1] and Kabbalists[2] there contains a severe prohibition to cut or trim the facial hair even with a scissor. Nevertheless many are accustomed to trim the hairs of the mustache that interferes with food.[3] One who trims his mustache is not required to wash his hands afterwards.[4]
[1] Tzemach Tzedek Yoreh Deah 93; See Sefer “Hadras Pnei Zakein” for all the opinions in Halacha that prohibit cutting the beard even with a scissor.
[2] Arizal in Shaar Hamitzvos Kedoshim and in numerous other places. See Sefer “Hadras Pnei Zakein” for all the opinions in Kabala that prohibit cutting the beard.
[3] See Sefer “Hadras Pnei Zakein” Chapter 11 p. 508 for many opinions that obligate cutting the mustache both according to Halacha and Kabala; The Rebbe answered that with regards to cutting the mustache there are sides to say it is permitted and sides to say it is forbidden and one should therefore ask Rabbanei Anash. [Shulchan Menachem 4:36 p. 133] The answer I [i.e. the author] received to this question from Rav Mordechai Ashkenazi, the Rav of Kfar Chabad, is that one may cut the mustache if it is in the way of food. [The question was asked as follows: “Is there any Hiddur involved not to cut the mustache even if it is in the way of food?”]
[4] Oar Letziyon 2:44-5; Halichos Shlomo 2:10