Praise be to Allah.
The puffer is a container in which there is a liquid medicine composed of three things: chemical substances (medical preparation), water and oxygen.
When pressure is applied to the puffer, the medicine comes out in the form of a mist. If the patient takes a deep breath in when applying pressure to the puffer, this mist enters the airway (trachea), but some of it remains in the pharynx, and a very small amount of it may enter the oesophagus.
Some contemporary scholars are of the view that using a puffer invalidates the fast. They said: Because the contents of the puffer may reach the stomach via the mouth, so it breaks the fast.
But most contemporary scholars are of the view that using this puffer does not break the fast, and this view is the correct one. They quoted a number of things as evidence for this:
The basic principle is that the fast remains valid, and this fact cannot be altered except when there is certain proof. Whether part of the mist from the puffer reaches the stomach is something uncertain: it may enter the stomach or it may not, because the basic principle is that this substance goes to the respiratory system, but some of it may enter the stomach. With this uncertainty we cannot say that it invalidates the fast. This is the answer to the evidence for the first opinion.
Assuming that some of this medicine does actually enter the stomach, it is forgiven, and does not invalidate the fast, by analogy with rinsing the mouth and using the miswaak.
With regard to rinsing the mouth: when the fasting person rinses his mouth, some of that water remains in his mouth, and some of that water may go down to the stomach. Hence if he rinses his mouth with water in which there is a radioactive substance, that radioactive substance will appear in his stomach after a while, which confirms that some of the water used for rinsing the mouth does go down into the stomach. But this part that goes down into the stomach is a very small amount, which is overlooked in sharee’ah. The ruling is that the fast is still valid if one rinses the mouth. The amount of medicine from a puffer that reaches the stomach – if any – is smaller than the amount of water that reaches the stomach when one rinses the mouth, so it is more likely that it does not break the fast.
As for the siwaak, it contains a substance that dissolves in the saliva and goes down into the pharynx, and then to the stomach. But Islam overlooks this, and does not regard it as invalidating the fast, because it is a small amount and is not intentional. Similarly the part that may go down into the stomach from the puffer is small, and the patient does not intend for it to enter the stomach, so it does not break the fast, by analogy with the miswaak.
Thus the strength of the second view is apparent. This is the view favoured by our contemporary scholars: Shaykh ‘Abd al-‘Azeez ibn Baaz (may Allaah have mercy on him), Shaykh Muhammad ibn al-‘Uthaymeen, Shaykh ‘Abd-Allaah ibn Jibreen, and the scholars of the Standing Committee. We have quoted some of their fatwas concerning this in the answer to question no. 37650.
See: Majallat al-Fiqh al-Islami (vol. 10, in which there are a number of articles about modern things that break the fast); Muftiraat al-Siyaam al-Mu’aasirah, by Dr. Ahmad al-Khaleel, p. 33-38.