The prohibitions of Yom Kippur apply to any male over the age of thirteen and any female over the age of twelve. Nonetheless, in situations where fasting can cause a life-threatening medical condition, there may be room for leniency, and in extreme cases it may be permissible to avoid fasting altogether. Before making any decision to eat or drink on Yom Kippur, it is advisable to consult with both a doctor and a rabbi.

Further reading: For more on the significance of fasting on Yom Kippur, see A Concise Guide to Mahshava, p. 67.

It is prohibited by Torah law to eat even a crumb or to drink even a drop on Yom Kippur. However, the severe punishment of karet that applies to one who eats or drinks on Yom Kippur applies only if the amount of food he ate was the volume of a date (approximately 30 cc) or he drank the amount of liquid that can fit into a person’s cheek. This latter measurement is subjective, and one can measure before Yom Kippur how much liquid fits into one of his cheeks. Consequently, in cases where it is medically warranted to eat or drink on Yom Kippur, one should eat or drink less than these quantities so as to minimize the violation. Even so, one must wait at least nine minutes between two acts of eating or two acts of drinking so that each act is judged individually, and the amounts do not combine. In more extreme circumstances, where there is possible danger to a person’s life even if he eats in these quantities, he may eat or drink as necessary.

The requirement to fast on Yom Kippur applies even to pregnant and nursing women and to those who are ill. However, in any case in which there is a possibility that fasting could cause a danger to life, one should not fast. One should consult with a doctor and a rabbi to determine if his medical situation warrants eating or drinking on Yom Kippur, and if so, in what quantities.

Within the first three days after childbirth a woman is entirely exempt from fasting. From the third to seventh day after childbirth she is not entirely exempt but there are leniencies that apply, and a rabbi should be consulted.

By Torah law, children under the age of bar and bat mitzva are not subject to any of the prohibitions of Yom Kippur. However, in order to communicate to them the importance of this day and in order to train them in the observance of its laws, it is customary to apply the following guidelines:

From the age when children are able to understand the nature of the day, even if only on a superficial level, it is customary to avoid washing them, anointing them, or having them wear leather shoes. Nonetheless, if it is particularly necessary to wash them, it is permissible.

From the age of nine, it is customary for them to wait to eat their meal later than usual.

From the age of eleven for girls and twelve for boys, it is customary for children to fast the entire day. However, if the child is weak and unable to fast the whole day, he can break his fast.

Once a girl turns twelve and a boy turns thirteen, they are considered adults in this regard and must fast the entire day and observe all the laws of Yom Kippur.

Further reading: For more on the importance of introducing children to mitzva observance from a young age, see A Concise Guide to the Sages, p. 404; A Concise Guide to Mahshava, p. 186.