Q. Can one sprinkle talc powder on the feet or shoes on Shabbos to keep them dry, specially on boots during the winter months?
A. Non-medicated talcum powder is made from talc, a mineral made up mainly of the elements magnesium, silicon, and oxygen. As a powder, it absorbs moisture well and helps cut down on friction, making it useful for keeping skin dry and helping to prevent rashes.
Poskim disagree if non-medicated talcum is still considered a medication. According to some opinions the drying effect is seen as a healing act. Tiferes Odom (3: 16), Cheshev Hoefod (2: 59), Igrois Moshe (O.H. 1: 114) permit its use even as a cosmetic, Piskei Teshuvos (328: 49: n. 397) quotes opinions that prohibit on the onset.
Horav Shlomo Miller’s Shlit’a opinion is to be lenient.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a