The laws of Yom Kippur take effect by sundown at the end of the ninth of Tishrei, and conclude with the emergence of three stars the following night. The exact times are publicized in synagogue calendars. The most well-known prohibition is that of eating and drinking, but there are four additional prohibitions included in the requirement of affliction: washing the body for pleasure, anointing, wearing leather shoes, and engaging in marital relations.

Further reading: For more on the talmudic source for these five prohibitions, see A Concise Guide to the Sages, p. 286.

The requirement to fast on Yom Kippur is quite strict, and in fact, this is the only fast day mandated by Torah law. Consequently, the rules governing this fast are more stringent than those governing other fasts. It is prohibited to put any food or drink into one’s mouth even without swallowing it. The fast is so important that if it is impossible for one to fast and also to attend synagogue and participate in the prayers, it would be better to stay home and fast than to attend the synagogue. Nonetheless, there are exceptional circumstances when it is permitted for a person to eat and drink, as will be explained below.

Washing the body or any part of it for pleasure is prohibited on Yom Kippur. Washing for cleanliness is permitted but should be conducted in a limited fashion, only as necessary. Following are some examples of when it is permitted to wash parts of the body in a limited fashion:

Upon waking up in the morning one should wash his hands until the knuckles (where the fingers connect to the hands).

Upon using the restroom, one may wash his hands until the knuckles. If there is a need to wash more than that due to cleanliness, one may do so but only what is absolutely necessary.

One who is feeding children may, to the extent necessary, wash his hands or wash a dish even though his hands will get wet.

Those who are ill (even if there is no danger to life) may wash themselves if necessary. This allowance applies as well to women in the days following childbirth.

It is prohibited to anoint any part of the body on Yom Kippur. This includes applying oil, cream, perfume, or any other product that soothes or nourishes the skin. One who is ill, or one who has a rash, may use a liquid (but not a cream) product to soothe his skin. However, if he is not sick, a medicated product may not be used due to the general prohibition against using non-essential medicinal products on any Shabbat or festival.

Further reading: For more information, see the chapter dealing with medicine on Shabbat, p. 439.

It is prohibited to wear leather shoes on Yom Kippur. Even if only a part of the shoes is made from leather it is prohibited to wear them. However, it is permissible to wear shoes made from any other material.

It is prohibited to engage in marital relations or any physical act that indicates closeness or intimacy. A couple should follow all the guidelines applicable when the wife is a nidda (see the chapter on the laws of family purity, p. 574).