Can I use mouthwash while fasting?

Rinsing the mouth is allowed

Muslims rinse their mouths several times a day in wudu, including in Ramadan. The Prophet ﷺ only asked fasting people to be gentle with it. He said: "Snuff up water freely, unless you are fasting" (Sunan Abi Dawud 2366). Scholars understood from this that putting water in the mouth or nose is fine, but you should avoid going so deep that it slips down your throat. Mouthwash works the same way: it goes in, you swish, you spit it out.

What if some goes down?

• A taste that stays in your mouth doesn't break the fast. Minty breath is not food.
• Tiny traces mixed with saliva that you can't avoid are forgiven. See Does swallowing my spit break my fast?
• Swallowing by accident: most Hanafi and Maliki scholars say a mistake while rinsing breaks the fast and you make up the day, while the Shafi'i and Hanbali schools excuse it if you weren't overdoing it. Either way, keep fasting for the rest of the day.
• Swallowing on purpose breaks the fast according to all scholars.

Some scholars prefer to avoid it

Because mouthwash is strong-tasting and easy to swallow by mistake, some scholars call it disliked (makruh) during the fast unless there's a need, like a mouth infection or dentist's advice. Others see no problem if you're careful. Both are reasonable. If you can, use it after iftar and at suhoor, and just rinse with plain water during the day.

Bad breath while fasting

Fasting breath is normal, and in Islam it isn't something to be ashamed of. The Prophet ﷺ said the smell from a fasting person's mouth is better to Allah than the scent of musk (Sahih al-Bukhari 1894). You can still look after your teeth. See Can I brush my teeth while fasting? For a fresh feeling without risk, drink plenty of water at night and avoid strong-smelling food at suhoor. Breath sprays are a different case: they spray straight towards the throat, so most scholars advise against them while fasting.