What exactly is the halacha regarding using liquid hand soaps on Shabbos and Yom Tov? Also, what about the kind becoming more popular nowawads- foaming hand soap, which foams as it comes out of the bottle? May these be used on Shabbos? Only on ones hands? What about the rest of the body?
The use of liquid soap on Shabbos in permitted according to most authorities, because the creation of foam is not considered a transgression of nolad (transformation to foam is not a change of state). Although Rav Moshe zt”l was seemingly stringent on the issue, the common custom is to be lenient. This would apply even to the “foaming hand soap” mentioned.
Sources: Shut Shaali Zion (Tinyana 1-2, no. 9, in the name of R’ Zvi Pesach Frank); Shemiras Shabbos (Chap. 12, no. 7, 21, in the names of Ketzos Hashulchan and R’ Shlomo Zalman Auerbach); Shut Pe’as Hasadeh (2:87, no. 4; 17:27, in the name of R’ Elyashiv shlita); Mibeis Levi (6, Tishrei 5755, p. 44, in the name of R’ Wosner shlita); Rivevos Efraim (8:154, citing the common custom, although he leans towards the stringent opinion of R’ Moshe).