When a person is suffering not just minor aches and pains but is actually ill, even if his condition is not life-threatening, he is permitted to take medicine and perform other actions that provide medical benefit, as long as they do not involve a prohibited labor. In severe situations he may even perform prohibited labors in certain ways (see below).

The following cases are ones in which the individual is defined as “ill” according to halakha:

A person who is in bed due to pain or illness.

A person who is in such pain that it emanates from the source of the pain and affects his entire body, e.g., someone suffering from a migraine.

A person who currently appears healthy but his condition will deteriorate if he does not receive treatment. Examples include people suffering from asthma, diabetes, and arthritis.

A person who suffered an internal wound or one of whose body parts is in danger, even if his state is not life-threatening in the present moment or in the future. An example of this is a broken bone.

A woman after childbirth, from the eighth day through the thirtieth day of birth. (Until the eighth day she is considered to be in life-threatening danger.)

In the case of young children, any medical need is treated like that of an actual illness for an adult, and therefore it is permitted to give them medicine (as noted in the next section, which addresses the laws regarding children on Shabbat).

When a person is injured and there is a concern about possible infection, the injury must be treated and dressed as required. In milder cases, the wound should at least be cleaned and disinfected.

There is a halakhic principle that “all are [deemed] ill with regard to cold.” This means that when it is especially cold, even a person who is halakhically defined as “healthy” is treated as a sick person. Consequently, if one forgot to turn on the heater before Shabbat on a particularly cold day, and the members of the family are suffering from the cold, and certainly if there is a sick person or small children in the house, it is permitted to ask a gentile to turn on the heater on Shabbat.

There are cases in which a person is not defined as currently ill but is nevertheless allowed to take medication on Shabbat, because he began the prescription before Shabbat and he must take the medication regularly over a period of time. Examples of this include one who began a treatment of antibiotics or fertility drugs.

It is prohibited to exercise on Shabbat.

A person who requires a hearing aid may use it on Shabbat, provided that the device was activated before Shabbat. It is permitted to adjust the volume.