Any of the following invalidates the fast: eating or drinking, sexual intercourse, telling lies about Allah and/or His Messenger (S), immersing the entire head in water, deliberate inhalation of smoke, remaining in the state of janabah (uncleanliness due to seminal discharge) till dawn, masturbating, taking injections whereby nourishing liquids reach the stomach, deliberate vomiting, intentionally passing an object through the throat or any other natural opening... Travelling, that is, going from your place of residence to a place situated at least eight farasikh (about twenty-seven and a half miles, or fifty miles according to some scholars) requires you to break your fast and to make up for it later on in equal number of days missed.
Deliberately breaking the fast requires a kaffara (atonement) which is either the feeding of sixty poor persons, or fasting for sixty consecutive days for each day missed. If the fast is broken accidentally, qaza (making up) suffices. Every adult and mentally sound male or female Muslim is required to fast starting twenty minutes before dawn and till sunset.
Al-Majlisi, on p. 352, Vol. 94, of his Bihar al-Anwar, cites a number of Shi’a scholars saying that they heard Imam Abu Ja’far al-Baqir (as) saying, "Telling lies breaks the fast, and so does a second look at another woman, in addition to oppression, be it little or much."
One who misses fasting a number of days during the month of Ramadhan due to travelling, forgetfulness, ignorance of the fact that those days were the days of the month of Ramadhan, sickness, menstruation or childbirth, are required to make up in equal number of days missed. Those who suffered from temporary insanity or who faint before having the chance to make the intention to fast, those who are afflicted with an ailment which causes them to be constantly thirsty and have no hope of healing, or because of old age that renders them feeble, do not have to make it up, nor do they have to offer kaffara, atonement.
One who falls sick during the month of Ramadhan and a year passes before being able to fully recover is, of course, not required to make up but to pay the compensation which is providing the needy and deserving poor, or providing one such person, with three quarters of a kilogram of food for each day missed. If one's father dies owing either prayers or fast, his oldest son is required to make up on his father's behalf, but a son is not required to make up on behalf of his deceased mother.
Fast is not accepted without the five daily prayers. Exempted from the fast are children, the mentally retarded, and old men and women who find it too hard to observe. If they can fast in other months to make up, it will be best for them. If they cannot make up, then they do not have to offer kaffara either. Women during their menstrual period are not only exempted from fasting, they are forbidden from fasting, but they will have to make it up later on. As soon as their period ends, they must take their ghusul (ceremonial bath) and resume the fast. Women breast-feeding their infants and whose natural milk is not sufficient, as well as women during their prenatal period may break their fast if it harms their infants. They, too, have to make up for the fast.