Swallowing Saliva or Phlegm While Fasting

Q: Does swallowing saliva or phlegm break the fast?

A: The rulings differ between ordinary saliva and phlegm.

Swallowing one’s normal saliva does not invalidate the fast, because it is unavoidable and continuous, and there is hardship in attempting to prevent it. However, if saliva exits beyond his lips and then he swallows it, the fast is invalidated. This is because it has exited its original place and is now treated as something external being reintroduced.

As for phlegm, if it rises to the mouth and a person swallows it, the fast is invalidated. This applies whether it originates from the head, throat, or chest. Once it reaches the mouth, swallowing it breaks the fast because avoiding it is not considered difficult, and for this reason it is impermissible to swallow it after it has reached the mouth. However, if it has not yet reached the mouth and remains within the throat or chest, the fast is not invalidated.

Likewise, if a person’s saliva becomes contaminated, such as being mixed with phlegm or other impurity, and he swallows it after it has become impure, the fast is invalidated. In summary, ordinary saliva does not break the fast so long as it remains within its normal place, but once it exits beyond the lips, or when phlegm reaches the mouth, swallowing it invalidates the fast.

Source: Sharh al-Muntaha & Sharh Ghayat al-Muntaha