1. THE FIRST CATEGORY OF VALID EXEMPTION: ILLNESS
Illness is any condition that takes a person outside the bounds of health as the result of some indisposition. Ibn Qudamah (d. 1223ce) said: “There is consensus among the scholars regarding the permissibility of breaking the fast due to illness in general, as stated in the verse of the Quran: Yet if one among you is sick or is on a journey, [such a person shall then fast] the same number of other days (Surat Al-Baqarah, 2:185).
The Companion (of the Prophet, on him be peace) Salamah ibn Al-Akwa‘ reported:
When the verse “wa ‘ala’l-ladhîna uûthiqunahu…” / “Yet for those who are hardly able to endure it…” (Surat Al-Baqarah, 2:184) was revealed, those who wanted to break their fast were allowed to break their fast and pay the redemption, until the verse “Shahru Ramadan alladhi…”’ / “It was the month of Ramadan in which…” (Sûrat Al-Baqarah, 2:185) was revealed and abrogated the one before it.
So, the prescription to fast went through stages. First, God permitted the believers to break their fast. Then God obligated the fast unless one had a valid justification for not doing so.
Illness remained a valid reason for not fasting, though not any illness or pain legitimately excuses one from fasting. If one fears that fasting will worsen the sickness, delay its cure, or cause damage to anything in the body, then one has a valid excuse for breaking the fast. In fact, one should break one’s fast under these circumstances, for the higher obligation is to keep oneself from becoming debilitated or, of course, from perishing.
If one is well, but feels the difficulty of fasting, this does not rise to the level of sufficient cause for breaking the fast. The exception here is the Hanafi legal school’s position that if one who is well believes it very likely the fast will cause him or her to fall ill, one can break the fast. If, however, the fear of illness is anxiety or apprehension of illness, more delusion or obsession than actuality, then it is not permissible to break fast.
The Malikis disagree with the Hanafis in this, holding that if the healthy person has no illness to begin with but merely harbors a fear that fasting will cause illness, then he or she is barred from breaking the fast because the fear of illness neither proves the likelihood of such an outcome, nor does it meet the standard of a sufficient legal proof authorizing action. If, however, one knows with great certainty that fasting will definitely cause real harm, he or she can break the fast. The distinction, then, is diagnosing the likely onset of real harm as a result of fasting as opposed to a difficulty caused by fasting, as difficulty in fasting is a wholly invalid justification.
Now, even though one who is ill ought to break the fast, it does not render his or her fast invalid if one chooses to complete the fast.
THE SECOND CATEGORY OF VALID EXEMPTION: TRAVEL
A. Travel defined and delimited
The kind of travel that allows one to break one’s fast must fulfill at least three conditions, and a fourth, according to all but the Hanafi juristic school:
1. DISTANCE: Enough for one to shorten the ritual prayer (about 50 miles, according to most scholars, but the norm, which is the better measure, is what is considered by people of the time and place a journey).
2. DURATION: The person in the state of travel or far from home does not have the intention of staying at that destination for more than three days. In this latter case, the person may be permitted to not fast during the travel (if they fulfill the requirements of distance, exceedance, and intentionality), but must resume the fast when they arrive at their destination of more than three days.
3. EXCEEDANCE: One must go beyond the limits of the city or town one is staying in. This means if one were to travel 50 miles but still be within his metropolitan or town area, it would not count as travel. The question of whether one’s metropolitan area remains as one’s town or home region should be taken seriously, such as Greater Chicago, for instance.
4a INTENTIONALITY: According to the majority of scholars, the person undertaking the journey must not be making it for unlawful reasons or to unlawful destinations, like a gambling trip to Las Vegas. This is because the allowance to break one’s fast is to make travel easy. If someone is undertaking an unlawful action, they are not included in the principle of creating ease for the traveler.
THE THIRD CATEGORY OF VALID EXEMPTION: AGE
There is consensus that it is permissible for the elderly not to fast. There is no specific definition for old age. It pertains to what people know and agree to be an age that is very advanced and disabling.

THE FOURTH CATEGORY OF VALID EXEMPTION: THIRST AND HUNGER
Severe thirst and grave hunger are both valid reasons not to fast, but not just any kind of acute thirst or hunger. If one really believes that the continuation of their fast will physically harm them because they are suffering from severe thirst or hunger, then it is permissible for them to break fast. If one in the military anticipates engagement and breaks the fast because of this likelihood, but engagement does not occur, there is no penalty for having broken the fast.

THE FIFTH CATEGORY OF VALID EXEMPTION: COERCION
If a faster’s well-being is threatened, such as it being said to a faster: “If you do not break your fast, you will be punished or confined,” there is no penalty if one breaks the fast under such duress. Yet one remains obliged to make up this missed fast.