Shaykh Ibn Uthaymeen was asked:
I suffer from allergies in my nose and I use a nasal spray as a cure. If I do not use it, then there will be great difficulty [on me] in terms of shortness of breathing. I am not able to be patient without treatment for more than three hours. If I do not use it, my breathing will be restricted completely. The difficult issue is that I will be entering the month of Ramadan such that I need to use the nasal spray and I fear it will ruin my fast. If I leave it off, I am not able to do so. Knowing that I will use it in some of the days of Ramadan and I will be very eager for the nasal spray not to reach my throat. So what is the ruling on that? What is the ruling on using it?
“This spray which you use is nothing except what resembles gas due to it evaporating and not reaching anything of the stomach. So then we say there is no harm in you using this spray while you are fasting, and it does not break the fast. This is because none of its parts reach the stomach because it evaporates and disappears. Mass/volume does not reach the stomach such that we can say that it leads to breaking the fast. So it is allowed for you to use it while you are fasting”.
[Noor ‘ala Darb no. 83]
Faisal bin Abdul Qaadir bin Hassan