Regarding acid reflux, there are different situations and conditions to consider:
– The first one is when the reflux does not reach the mouth. In this case, it does not invalidate the fast unanimously, and no additional actions are required.
– The second is when the reflux reaches the mouth. If one spits it out without swallowing, there is no obligation upon them. However, if one swallows it, according to the majority opinion, it breaks the fast. According to our school of thought, the fast is only invalidated if the reflux separates from the mouth.
Fatwa by Dr. Khālid Naṣr