Is teeth whitening haram?

No, teeth whitening is generally not haram. Many scholars allow it when it only removes stains or brightens your natural tooth colour, the method is safe and it isn't done to show off. What Islam warns against is cutting or filing teeth to change their shape, which is a different thing.

Whitening is not the same as filing

The hadith that worries people is about filing. Abdullah ibn Mas'ud said that Allah has cursed women who "create a space between their teeth artificially to look beautiful" and who "change the features created by Allah" (Sahih al-Bukhari 5931). Scholars understand this as permanently cutting or reshaping healthy teeth just for looks.

Whitening does something else. It lifts stains left by tea, coffee or smoking and brings back the colour your teeth already have. Nothing is cut, removed or added, so many contemporary scholars treat it like cleaning rather than changing Allah's creation. For the filing question, see Are dental veneers and teeth filing haram?

Caring for your smile is encouraged

Islam never asks you to neglect your appearance. When a man worried that liking fine clothes might be arrogance, the Prophet ﷺ answered that Allah is graceful and loves grace, and that pride means looking down on people (Sahih Muslim 91). The Quran asks the same kind of question:

قُلْ مَنْ حَرَّمَ زِينَةَ ٱللَّهِ ٱلَّتِىٓ أَخْرَجَ لِعِبَادِهِۦ وَٱلطَّيِّبَـٰتِ مِنَ ٱلرِّزْقِ "Ask, [O Prophet,] 'Who has forbidden the adornments and lawful provisions Allah has brought forth for His servants?'" Quran 7:32

What's fine and what to watch

Professional cleaning and dentist-supervised whitening: fine, and usually the safest route.
Whitening toothpaste and strips: fine if you follow the instructions. Overuse can make teeth sensitive and wear down enamel.
Harsh home hacks: avoid scrubbing with abrasive powders or acids. The Prophet ﷺ said, "There should be neither harming nor reciprocating harm" (Sunan Ibn Majah 2340), and that includes harming yourself.
Intention: brightening your smile for confidence or work is fine. Doing it to look down on others is not.

Practical points for worship

Remove trays or strips before wudu so water reaches your mouth, and don't swallow any gel. If you're fasting, book treatments for after iftar. See Can I brush my teeth while fasting?

The sunnah way to a clean smile

The Prophet ﷺ said the siwak is a means of purification for the mouth and pleases the Lord (Sunan an-Nasa'i 5). Brushing twice a day, flossing and using a miswak do most of the work of keeping teeth healthy and bright. See What is a miswak and do I have to use it?

Key points

Whitening removes stains; it doesn't reshape teeth.
The hadith against filing teeth for beauty doesn't cover ordinary whitening, according to many scholars.
Keep it safe, and don't do it out of pride.
Brushing and the siwak are the sunnah basics.

Tip: Ask your dentist for a professional clean first. It often brightens teeth on its own, and it's the cheapest, gentlest step.