Fasting is an obligation, but Islam does not place hardship on people. The Qur'an gives clear concessions, and says that Allah intends ease and not hardship.

The first concession is for illness and travel. In Surah Al-Baqarah, chapter two, verse one hundred and eighty-four, an English translation of the meaning reads: “So whoever among you is ill or on a journey during them - then an equal number of days are to be made up.” Aisha reported that a companion, Hamzah ibn Amr al-Aslami, asked the Prophet, peace be upon him, whether he should fast while travelling, and he replied: “You may fast if you wish, and you may not fast if you wish.” That is in Sahih al-Bukhari, number nineteen hundred and forty-three. Many scholars consider fasting better on a journey if it causes no hardship, while others prefer taking the concession. All agree that hardship makes the concession preferable. What counts as a journey is discussed by scholars in the same way as for shortening the prayer.

Second, a woman who is menstruating, or in postnatal bleeding, does not fast. Aisha said that the women of her time were ordered to make up the fasts, but not the prayers, in Sahih Muslim, number three hundred and thirty-five.

Third, the elderly and the chronically ill. The same verse speaks of those who are able to fast only with hardship, who give “a ransom as substitute of feeding a poor person each day.” Most scholars apply this to an elderly person, or someone with a lasting illness who cannot be expected to recover. This payment is called fidya. Most schools require it; in the Maliki school it is recommended rather than required.

Fourth, pregnancy and nursing. If fasting would harm a pregnant or nursing mother, or her child, she may break the fast. Scholars differ on what she owes afterwards. In outline, the Hanafi school requires only making up the days. The Shafi'i and Hanbali schools require making up the days, plus feeding a poor person for each day if she feared for the child, rather than only for herself. And the Maliki school requires making up for a pregnant woman, and making up plus feeding for a nursing mother.

If you have a health condition and are unsure whether you can fast, talk to a doctor about the risks, and to a knowledgeable teacher about what is required. Protecting your health is part of the guidance. And for your own school's details, follow your school or a trusted teacher.