journey (safar):
it is allowable for the traveler to break his fast while traveling, whether he is subjected to rigors and hardships during his travels or not.

sickness (marad):
if one has an illness that would be worsened by fasting, or fasting would delay the cure, the fast may be abandoned. for example, a person with diabetes may have to eat every few hours to maintain his blood sugar level, or an epileptic may have to take his medicine at regular intervals to prevent a seizure.

pregnancy (haml):
if a woman feels that if she fasts, the fetus will be harmed or she herself will be weakened dangerously, she is permitted to leave the fast.

breast-feeding (rida'ah):
if a breast-feeding mother or wet-nurse feels that fasting would he harmful to the baby or herself she is allowed to abandon the fast.

weakness (da'f) or old age (kibar as-sinn):
 (a) if a person is convalescing (regaining his strength)
      after an illness and fears that the fast would make       him sick again, he is allowed to defer fasting.

 (b) if a person has become extremely weak due to old
      age, he is allowed to abandon fasting.

jihad (war):
 (a) if a person is about to participate in jihad and
      fears that the fasting would weaken him, he may defer the fast.

 (b) if jihad is in progress, participants are allowed to
      postpone the fast.