Short answer
Mucus that runs down from your nose into your throat does not break the fast. But dried mucus that you pick out of your nose and then eat has left the body, so in the Hanafi school swallowing it breaks the fast and you make up one day. If you did it forgetting you were fasting, the fast is fine.
Mucus drawn down from the nose or head into the throat and swallowed does not break the fast. Dried mucus taken out of the nose and then put in the mouth and swallowed counts as something from outside, so the fast is broken with one day of qada and no kaffarah, as it is not food.
Other madhhabs
- Shafi'i
- Mucus that reaches the outer part of the mouth and is then swallowed on purpose breaks the fast.
- Hanbali
- Swallowing mucus once it has reached the mouth breaks the fast in the main view.
Explanation
This sounds like a joke question, but the answer shows a real principle of fasting. In the Hanafi school, what comes from inside your body and stays inside, such as saliva or mucus sliding down the back of the throat, does not break the fast. What has left the body and is then taken back in through the mouth is treated like anything else from outside.
Two cases:
- Sniffing mucus back, or feeling it run down your throat: the fast is fine. See swallowing mucus and saliva.
- Picking dried mucus from the nose and eating it: it has left the body, so swallowing it breaks the fast. Make up one day after Ramadan. There is no kaffarah, because it is not food.
Your own saliva follows the same rule: swallowing it from inside your mouth is fine, but saliva that has left your mouth onto your hand and is then licked back breaks the fast.
Beyond the fast. Eating mucus is something people find disgusting, and Islam teaches cleanliness. Use a tissue and wash your hands. If you did it while forgetting that you were fasting, the fast is not broken at all, just as with eating by forgetfulness: see eating by mistake.
The evidence
Quran, Surah Al-Baqara 2:187
أُحِلَّ لَكُمْ لَيْلَةَ ٱلصِّيَامِ ٱلرَّفَثُ إِلَىٰ نِسَآئِكُمْ ۚ هُنَّ لِبَاسٌۭ لَّكُمْ وَأَنتُمْ لِبَاسٌۭ لَّهُنَّ ۗ عَلِمَ ٱللَّهُ أَنَّكُمْ كُنتُمْ تَخْتَانُونَ أَنفُسَكُمْ فَتَابَ عَلَيْكُمْ وَعَفَا عَنكُمْ ۖ فَٱلْـَٰٔنَ بَٰشِرُوهُنَّ وَٱبْتَغُوا۟ مَا كَتَبَ ٱللَّهُ لَكُمْ ۚ وَكُلُوا۟ وَٱشْرَبُوا۟ حَتَّىٰ يَتَبَيَّنَ لَكُمُ ٱلْخَيْطُ ٱلْأَبْيَضُ مِنَ ٱلْخَيْطِ ٱلْأَسْوَدِ مِنَ ٱلْفَجْرِ ۖ ثُمَّ أَتِمُّوا۟ ٱلصِّيَامَ إِلَى ٱلَّيْلِ ۚ وَلَا تُبَٰشِرُوهُنَّ وَأَنتُمْ عَٰكِفُونَ فِى ٱلْمَسَٰجِدِ ۗ تِلْكَ حُدُودُ ٱللَّهِ فَلَا تَقْرَبُوهَا ۗ كَذَٰلِكَ يُبَيِّنُ ٱللَّهُ ءَايَٰتِهِۦ لِلنَّاسِ لَعَلَّهُمْ يَتَّقُونَ ﴿١٨٧﴾
It has been made permissible for you the night preceding fasting to go to your wives [for sexual relations]. They are clothing for you and you are clothing for them. Allah knows that you used to deceive yourselves, so He accepted your repentance and forgave you. So now, have relations with them and seek that which Allah has decreed for you. And eat and drink until the white thread of dawn becomes distinct to you from the black thread [of night]. Then complete the fast until the sunset. And do not have relations with them as long as you are staying for worship in the mosques. These are the limits [set by] Allah, so do not approach them. Thus does Allah make clear His ordinances to the people that they may become righteous.
The fast means nothing from outside is swallowed from dawn to sunset.
Sahih al-Bukhari 1933
Sahih... إذا نسي فأكل وشرب فليتم صومه فإنما أطعمه الله وسقاه ...
"If he forgets and eats or drinks, let him complete his fast, for it was Allah who fed him and gave him drink."
Something swallowed out of forgetfulness does not break the fast.
Where the ruling is recorded
- al-Fatawa al-Hindiyya, Kitab al-Sawm, chapter on what breaks the fast and what does not. Mucus drawn from the head into the throat and swallowed does not break the fast according to Abu Hanifa and Muhammad.
- Radd al-Muhtar (Ibn Abidin), Kitab al-Sawm, chapter on what breaks the fast and what does not. Saliva that has left the mouth and is then swallowed breaks the fast.
Checked by our team. For a more accurate answer to your own situation, consult a scholar. Quran translation by Sahih International. Hadith Arabic from the standard editions of the six books and the Muwatta, with gradings as recorded there; the English is our own rendering. Spotted a mistake? Tell us.