Short answer
Some things do not break the fast but are makruh (disliked) in the Hanafi school: tasting or chewing something without need, toothpaste, gathering saliva to swallow it, rinsing the mouth or nose too deeply, kissing when not sure of yourself, and effort that may weaken you into breaking the fast. Sins such as lying are worse than all of these.
Makruh tanzihi for the fasting person: tasting or chewing something without need, toothpaste or tooth powder, gathering saliva and swallowing it, going deep when rinsing the mouth and nose, kissing or touching a spouse when not sure of self-control, and cupping or heavy effort that may weaken you. The miswak, kohl, oil on the hair or moustache, perfume and a cooling bath are not disliked.
Other madhhabs
- Shafi'i
- Using the miswak after midday is disliked for the fasting person.
- Maliki
- Kohl, tasting food and smelling perfume are disliked, and kohl that reaches the throat means making up the day.
- Hanbali
- The miswak after midday is disliked, and kohl whose taste reaches the throat breaks the fast.
Explanation
Fasting has three layers. The first is what breaks it, which the what breaks your fast checker lists. The second is what is makruh: the fast stays valid, but its quality drops, either because the act brings you close to breaking it or because it goes against the spirit of fasting. The third, and the most serious, is sin.
Makruh in the Hanafi school:
- Tasting or chewing something without a need. A cook checking the salt, or a mother chewing food for a baby with no other option, is excused. See chewing gum and tasting food.
- Toothpaste, tooth powder and mouthwash during the day. See brushing your teeth.
- Collecting saliva in the mouth and then swallowing it.
- Rinsing the mouth or sniffing water deeply in wudu. The Prophet ﷺ told a Companion to sniff water deeply except when fasting.
- Kissing or touching your spouse when you are not sure you will stop there.
- Cupping, giving a lot of blood or hard exertion that may weaken you to the point of breaking the fast.
Not disliked: the miswak at any time, kohl and eye drops, oil on the hair or skin, perfume, a shower or wet cloth to ease the heat, and sleeping.
Sins are worse. Lying, backbiting, swearing, looking at what is haram and fighting do not break the fast, but they can empty it of its reward. The Prophet ﷺ said that whoever does not give up false speech and acting on it, Allah has no need of his leaving his food and drink. See swearing and lying while fasting.
The evidence
Quran, Surah Al-Baqara 2:183
يَٰٓأَيُّهَا ٱلَّذِينَ ءَامَنُوا۟ كُتِبَ عَلَيْكُمُ ٱلصِّيَامُ كَمَا كُتِبَ عَلَى ٱلَّذِينَ مِن قَبْلِكُمْ لَعَلَّكُمْ تَتَّقُونَ ﴿١٨٣﴾
O you who have believed, decreed upon you is fasting as it was decreed upon those before you that you may become righteous -
The aim of fasting is taqwa, so whatever weakens the fast or its spirit is disliked.
Sahih al-Bukhari 1903
Sahih... من لم يدع قول الزور والعمل به فليس لله حاجة ...
"Whoever does not give up false speech and acting on it, Allah has no need of his leaving his food and drink."
Sins do not break the fast but ruin its purpose.
Sunan Abi Dawud 142
Graded sahih... وبالغ في الاستنشاق إلا أن تكون صائما ...
"Sniff the water deeply, unless you are fasting."
Going deep in rinsing the nose is avoided while fasting because water may go down.
Where the ruling is recorded
- Nur al-Idah with Maraqi al-Falah, Kitab al-Sawm, chapter on what is disliked and not disliked for the fasting person. Tasting, chewing, gathering saliva and kissing when not safe are disliked; kohl, oil and the miswak are not.
- al-Hidaya, Kitab al-Sawm, chapter on what requires qada and kaffarah. Tasting or chewing something is disliked for the fasting person; there is no harm in kohl or oiling the moustache.
- al-Majmu' (Nawawi), Kitab al-Siyam. The Shafi'i dislike of the miswak after midday for the fasting person.
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.