[One who cuts his hair is required to wash his hands one time immediately afterwards. This applies even if he only cut a small amount of hair, and applies whether the hair was cut with a scissor or razor.] If one does not wash his hands after cutting his hair, he will have inner fear for three days.
Must one wash his hands after cutting someone else’s hair?
Must one wash their hands if another person cut his hair?
Must one wash his hands after cutting facial hair such as the mustache?
According to many Poskim and Kabbalists 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. One who trims his mustache is not required to wash his hands afterwards.
Must one wash his hands after being honored to cut some hair by an Upshernish?
 Kama 4/19
 See Halacha 3 in footnotes for the full analysis in this matter.
Ketzos Hashulchan 2/11; This is due to the impure spirit which resides on the hand after a haircut. This applies according to all Poskim. [See Halacha 2 in footnotes] Vetzaruch Iyun why this was not listed in 4/18.
Kaf Hachaim 4/68 in name of Poskim; Kaf Hachaim [Falagi] 8/27
Kaf Hachaim 4/93
Kaf Hachaim 4/92; Yifei Laleiv 1/18 [Kuntrus Achron] that so is the custom of the world.
As it is common for the barber to touch the persons hair which is full of sweat.
Kaf Hachaim 4/92
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.
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.
 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?”]
 Or Letziyon 2/44-5; Halichos Shlomo 2/10
Halichos Shlomo 2/10; Yalkut Hatispores p. 77 by Rav Y.Y. Sarabranski. There he explains that perhaps the cutting of a few locks of hair does not cause the evil spirit to reside.
 See Piskeiy Teshuvos 4/28 footnote 265; Rav Avraham Pariz would wash his hands three times inconsecutively after cutting a curl of hair from the three year old boy. [Keitzad Nechaneich Yiladeinu p. 172]