A very small amount (1/20 ml.) of the spray that lung patients use is delivered into the mouth at one time. Most of it is absorbed by the mouth and the wall of the trachea and disappears. There is no certain information that the rest reaches the stomach with the saliva. When that amount is compared to the water that remains in the mouth during wudu (ablution), it can be seen that it is very little. As a matter of fact, there is a hadith (Darimi, Sawm, 21) and the consensus of Islamic scholars that if the water remaining in the mouth after wudu reaches the stomach, it does not invalidate fasting. Hazrat Prophet used miswak while he was fasting. (Bukhari, Sawm, 27; Tirmidhi, Sawm, 29). On the other hand, fasting is not invalidated by something that is not certain whether it reaches the stomach or not according to the rule “what is known as certain is not invalidated by doubt”.

For this reason, oxygen sprayers that asthmatic patients use in order breathe easily do not invalidate the fast.