The central mitzva of Yom Kippur is: “You shall afflict yourselves” (Leviticus 16:29). The Sages determined that this affliction consists of five prohibitions.

On Yom Kippur one is prohibited from eating, drinking, bathing, smearing oil on one’s body, wearing leather shoes, and conjugal relations. But a king, and a bride in the days immediately after her marriage, may wash their faces, and a woman after childbirth may wear shoes; this is the statement of Rabbi Eliezer, but the Rabbis prohibit these. (Mishna Yoma 8:1)