Gemara

Question: What do the five Inuyim (afflictions) of Yom Kipur correspond to? (There are five in all, for drinking is included in eating.)

Answer (Rav Chisda): They correspond to the five commands about Inuy.

Rishonim

The Rif cites Rav Chisda.

Suggestion (Ran DH Yom): The Inuyim are mid'Oraisa. If not, the Gemara would not need to say that one is not Chayav Kares for them. However, only eating and drinking are explicit in the Torah. Chachamim were authorized to set the guidelines for the other four. They permitted whatever is not done for pleasure.

Rejection (Ran): They cannot be mid'Oraisa. One may not overtly cause a minor to transgress an Isur mid'Oraisa, yet one may bathe and anoint minors on Yom Kipur! Also, Chachamim did not enact to Mechanech (train) children to refrain from them. This is understandable only if they are mid'Rabanan.

Defense of suggestion (Beis Yosef OC 611 DH v'Li): One may feed children, even though eating is explicitly forbidden. All the more so the other Inuyim are permitted to them! Chachamim did not forbid things that promote children's growth. The Tur says that we do train children to refrain from the other Inuyim.

Rambam (Hilchos Shevisas Asor 1:5): We have a tradition that bathing, anointing, wearing shoes and marital relations are forbidden. It is a Mitzvah to refrain from them, just like from eating and drinking. One is not Chayav Kares or Korban for them, but one is lashed mid'Rabanan for them.

Lechem Mishneh: The Rambam holds that the other Inuyim are mid'Oraisa. He does not count them like a separate Mitzvah because they are not included in Inuy of the verse. Rather, "'Shabason" alludes to them.

R. Mano'ach: The Rambam holds that the four Inuyim are mid'Rabanan.

Rosh (8:1): The four Inuyim are mid'Rabanan. The Gemara does not ask what is the source for them, rather, what do they correspond to, i.e. why did Chachamim enact (four) so there will be five in all. Also, we attribute them to "Shabason", just like do for Shevus (Isurim mid'Rabanan of Shabbos). Also, Chachamim were lenient for a Kalah and a king. Also, the Yerushalmi says that regarding Yom Kipur, anointing is not like drinking regarding punishment or Isur.

Poskim

Shulchan Aruch (OC 611:1): ...One is Chayav Kares only for Melachah, eating and drinking.

Magen Avraham (1): All the Inuyim are mid'Oraisa.

Mishnah Berurah (3): We have no source that the Shulchan Aruch considers the other Inuyim to be mid'Oraisa. If they are mid'Oraisa, one must be stringent regarding a Safek. It is proper to be stringent like the opinion that they are mid'Oraisa.