2. The reason why the above actions require washing of the hands: [1]
The impure spirit resides on one’s hands after any of the above actions are done. It is for this reason that one is required to specifically wash his hands with water, as opposed to other cleaning methods, after any of the above actions are done [see next Halacha].
[1] Ketzos Hashulchan 2:11; See Admur 97:3 regarding touching a louse; Admur 128:27 regarding touching shoes; Seder Hayom; See Kaf Hachaim 4:61 and Piskeiy Teshuvos 4:18. Poskim listed in “Other Opinions.”
Background: The reason for the requirement to wash hands after doing any of the above listed actions is because an impure spirit resides on ones hands after any of these actions are done. This is learned from the fact Admur rules that only water may be used as opposed to other items that clean. [Ketzos Hashulchan 2:11; This is also understood from Admur 97:3 which explicitly states that washing with water is required when touching a louse due to that the impure spirit resides on the hands upon touching it. Admur 128:27 writes one must wash his hands after touching his shoes due to the danger of the impure spirit.] This impure spirit is not the same impurity that resides on the hands upon awakening in the morning [called Bas Melech]. [Seder Hayom in name of Makor Chaim; brought in Kaf Hachaim 4:61]
Other Opinions: Some Poskim rule that not all of the above mentioned actions bring an impure spirit and rather some require cleaning simply because they dirty the hand and prevent one from being allowed to learn Torah. [Machatzis Hashekel 4:17; Nivei Shalom 4:12; Machazik Bracha brought in Shaareiy Teshuvah 4:12; Soles Belula 4:14 in name of Makor Chaim (student of Arizal); Ben Ish Chaiy Toldos 17; M”B 4:41] Admur however holds that they all cause impurity, being that he rules that only washing with water helps for any of these actions. The following Poskim rule like Admur that all the above actions bring impurity: Kisei Eliyahu 4:6; Levush 4:18; Olas Tamid 4:18; Yifei Laleiv 4:18 in name of Mor Uketzia; Peri Megadim 4 M”Z 14; Rashal brought in Tehila Ledavid 4:24; Derech Chaim; Piskeiy Teshuvos 4 footnote 178 and so is implied from many Poskim. [brought in Kaf Hachaim 4:60] The following actions bring the evil spirit according to all: awaking from sleep; bathroom; bathhouse; bloodletting; cutting hair and nails; marital relations. The following actions are debated by the Poskim above regarding if they bring the evil spirit: touching covered areas; scratching head; lice; touching shoes. [Soles Belula ibid; Piskeiy Teshuvos 4:18]