sexual intercourse during the time of day for fasting. willful violation of fast by such practice requires the fast of sixty consecutive days in order to make up for the day in which the intercourse took place.
intentionally ejaculating. unintentional ejaculations do not break the fast.
eating, drinking, smoking or taking any food substitutes such as receiving blood, glucose, or i.v. substances by intention while knowing you should be fasting. if done without remembering you are fasting, then it would not count as breaking the fast. if such an act was prescribed for an essential reason, the fast would be consider broken but would only require one day for each day missed.
vomiting on purpose without necessity.
days in which the above practices (2 through 5) are to be make up a day for a day once ramadan is over.
on the other hand, the application of khol, eye, ear, or nose drops or brushing the teeth or gargling with water do not break the fast. as long as there is no intention of taking any nourishment internally.
wearing perfumes, using siwak or toothbrush without toothpaste do not break fast since it has been reported that the prophet (peace be upon him) practiced that. one can also take the shower or a bath while fasting. however, it is incumbent to make intention of fasting before dawn. such intention is to be made in the mind only. pronouncing certain words for that intention is a bid'ah (innovation) neither the prophet (peace be upon him) nor were his companions ever reported to have composed certain words for the intention.