Must one wash his hands if he touched sweat?
One who touched sweat that came from the covered areas of the body is to wash his hands afterwards. Thus if one touched sweat found under a Kipa or hat or by the underarms of a shirt, he is to wash his hands.[1] If however he touched sweat of the uncovered areas, he is not required to wash his hands. Thus touching perspiration of the face, hands and neck does not require hand washing.[2]
[1] Sheivet Halevy 8:2; However see Kaf Hachaim 4:98 in name of Ruach Chaim that one is not required to wash his hands after touching a sweat filled shirt, even if the sweat came from covered areas of the body. Ashel Avraham Butchach 4 rules likewise that one is not required to wash the hands, although he concludes it is an attribute of piety to do so. Halichos Shlomo 20:17 in name of Rav SZ”A is lenient and so rules Piskeiy Teshuvos 4:30
[2] Ashel Avraham Butchach 4; Kaf Hachaim 4:98 in name of Ruach Chaim; Piskeiy Teshuvos 4:23; The reason for differentiating between sweat of the revealed parts of the body and covered parts of the body is because only the seat of the covered parts is considered contaminated and brings the evil spirit. [Kaf Hachaim ibid]