Eating and drinking the primary invalidator of fasting, which is the number one cause of the invalidation of fasting, is eating and drinking. Naturally, swallowing anything, whether edible, such as bread and water, or inedible, such as the leaves of trees, whether in large amounts or small, will invalidate fasting if it is done intentionally. But if eating or drinking is done inadvertently or due to forgetting, it will not invalidate one's fast. But swallowing the saliva does not invalidate fasting even if the amount of saliva is more than usual due to thinking of something sour, etc. Also it is permissible to swallow phlegm as long as it has not entered the mouth, but if it enters the mouth, one must spit it out based on the obligatory precaution. Therefore, if the phlegm enters one's mouth and one intentionally swallows it, one will have to pay the expiation, kaffārah, of an intentionally broken fast for it. Even if this occurs to one during prayer and one does not have any tissues to spit the phlegm in to, it is permissible to break the prayer. If you get nosebleeds a lot, you do not need to worry because nosebleeds do not invalidate fasting unless the blood enters the mouth and is swallowed intentionally or by keeping the head up to stop the bleeding or sniffing, you make some of the blood enter the throat. What is meant here by the mouth encompasses the area between one's lips and the throat where the letter kh is pronounced. Touching the lips with one's tongue will not create a problem for fasting as long as the lip has not been moist or covered in some substance like cosmetics. Things like trying to chew the food for children, tasting the food, rinsing the mouth with water or mouthwash will not invalidate fasting as long as these things are not swallowed, but even if some of it inadvertently reaches the throat, it will still not invalidate fasting. However, if one knows for sure that this would cause some of the substances to reach the throat, and they do that anyway, their fasting is void and the kaffārah must also be paid. Wearing makeup and using kohl will not invalidate fasting, but using kohl is considered abominable makrooh if the smell or the taste of kohl reaches the throat while one is fasting. But chewing gum invalidates fasting because as one chews the gum, small particles of it break off and are swallowed.