One of the things which can invalidate fasting is when a fasting person does something to intentionally throw up. In such a case, the person in question must pay expiation in addition to observing the qada fast. Also, if an individual knows that eating certain foods will make them throw up, the recommended precaution demands that they avoid eating those foods. So, if they eat such foods and then throw up during the day, their fasting will be invalidated. In cases where a fasting person has to throw up intentionally due to food poisoning or for the treatment of some illnesses, their fasting will be invalidated, but they do not need to pay any expiation for it and they only need to observe the qada fast. However, in cases that a fasting person throws up involuntarily or they do it intentionally while they have forgotten that they are fasting, their fasting will not be invalidated. In addition to the five invalidators of fasting which have already been discussed, sexual intercourse, masturbation, remaining in the state of Janābah and anima are the other things which invalidate fasting. In order to learn more about the Islamic laws regarding these invalidators of fasting, refer to the book of Practical Laws of Islam by Ayatollah Makarem Shirazi or his Eminences Office website. A few important points. 1. If one does any of the nine invalidators of fasting inadvertently or out of forgetfulness, they will not invalidate one's fasting. The only exception to this rule is the case of remaining in the state of Janābah where a person sleeps while being junub and does not perform ghusl until the fajr time or forgets to perform ghusl until fajr. In this case, the fasting of the person in question will be problematic. 2. If a fasting person is forced to do any of these invalidators of fasting, for example, if someone forces their head underwater, their fasting will not be invalidated. However, if a fasting person is forced to break their fast themselves, like when a powerful person threatens them, that if they do not do that, it would hurt them or cause them some substantial material damage. They can break their fast and their fast is void. However, they only need to observe the qada fast. 3. There are also cases where a fasting person inadvertently does one of the acts that invalidate fasting and then does that act again, thinking that their fasting was invalidated the first time. In such cases, the obligatory precaution demands that they avoid doing anything else that could invalidate their fasting until the time of iftar and then observe the qada fast as well. Nevertheless, they do not need to pay any expiation for this.