מנין לסיכה שהיא כשתייה ביום הכפורים אף על פי שאין ראיה לדבר זכר לדבר שנאמר ותבא כמים בקרבו וכשמן בעצמותיו:
From where [is it derived] anointing is like drinking on Yom Kippur? Although there is no proof for this matter, there is an allusion to this matter, as it is stated: And it came like water into his internal [organs] and like oil into his bones.
Elsewhere,1 the Mishnah permits kings and newlywed brides to wash their faces on Yom Kippur. The Gemara2 adds that although it is generally forbidden to anoint even a part of one’s body, a person who is ill or who has scabs on his head may anoint himself. Tosafos Yeshanim3 deduces from these leniencies that all the afflictions that are put into practice on Yom Kippur, aside from the prohibitions to eat and drink, are of rabbinic origin. Otherwise, how could they be permitted under any circumstances that are less than life-threatening? However, Tosafos Yeshanim then rejects this deduction, suggesting instead that washing and anointing may well be Torah prohibitions, but that the Torah prohibition only applies to washing or anointing the entire body. On the other hand, the above cases in which leniencies were permitted are ones in which only part of the body is being washed or anointed. Partial washing and anoiniting may indeed be rabbinic decrees while full washing and anointing are Torah law.
The Gadol MeMinsk4 questions this suggestion of Tosafos Yeshanim: If full washing and anointing are Torah prohibitions, then partial washing and anointing should also be Torah prohibitions, based on the principle: chatzi shiur asrah Torah - the Torah forbade partial measures,5 ruling out any leniency?
Emel Berachah6 answers the Gadol MeMinsk’s question: That which the Torah forbade even partial measures is only where the full “measure” is precisely that: a quantity - i.e., the quantity that is necessary in order to be considered in full violation of a prohibition or in fulfillment of a commandment, and therefore subject to temporal punishment. For example, it is forbidden to eat pork. In order be considered in full violation of the prohibition and therefore subject to flogging, one must consume the volume of an olive of pork. However, the prohibition forbids eating even less that the volume of an olive of pork, which is qualitatively the same act, involving the same pleasure, as eating the volume of an olive of pork.
On the other hand, in the cases of washing and anointing on Yom Kippur, the concept of “full-body” washing and anointing is not a concept of quantity, but a concept of quality - i.e., the Torah requires a person to afflict himself on Yom Kippur, by depriving himself of certain pleasures. These pleasures include washing and anointing one’s entire body. But they do not include paritial washing and anointing because these are qualitatively less pleasurable - partial washing and anointing are not just less in quantity, but also of a lower quality than full washing and anointing. Thus, the principle of chatzi shiur asrah Torah is not applicable in this case, and, perforce, the prohibition of the qualitatively lesser pleasure of partial washing and anointing is only a rabbinci decree.
מסכת יומא דף ע"ג ע"ב: והמלך והכלה ירחצו את פניהם.
שם דף ע"ז ע"ב: אסור לסוך מקצת גופו ככל גופו ואם היה חולה או שהיו לו חטטין בראשו סך כדרכו ואינו חוש.