How does teeth whitening work?
Teeth whitening is simple chemistry, but the details decide whether it suits you, how long it lasts and what it means for any crowns, veneers or fillings you already have.
Medically reviewed by Dt. Hüseyin Yavuz Özbek, implant surgeon · Updated October 2026Teeth whitening works by placing a peroxide gel on the teeth. Hydrogen peroxide, or carbamide peroxide which breaks down into it, passes through the enamel and breaks up the coloured molecules that make teeth look yellow or grey, so the tooth reflects more light. It can be done in a dental clinic in about an hour or at home with custom trays over two to six weeks. It only lightens natural teeth: crowns, veneers, fillings and dentures do not change colour.
How teeth whitening works is a fair question to ask before you put any gel on your teeth. It is not a coating and it is not a polish. It is a chemical reaction inside the tooth. Once you understand that, it becomes much easier to see who whitening suits, why it sometimes causes sensitivity, and why it does nothing at all to crowns, veneers or fillings. Our dentists explain the process step by step below.
Why teeth darken in the first place
A tooth has a hard, slightly see-through outer layer called enamel, and a softer, naturally yellower layer underneath called dentine. The colour you see is mostly the dentine showing through the enamel.
Teeth darken for two broad reasons:
- Stains from outside. Tea, coffee, red wine and tobacco leave coloured molecules on and in the outer enamel. Some come off with a scale and polish. Others work their way deeper.
- Changes from inside. With age, enamel slowly thins and the dentine underneath becomes thicker and darker. More yellow shows through. A tooth that has died or had a root canal can also turn grey from the inside.
The Oral Health Foundation notes that teeth naturally darken with age as well as from staining, which is why whitening questions come up so often in patients over 50.
The chemistry, in plain English
Professional whitening gels contain either hydrogen peroxide or carbamide peroxide. Carbamide peroxide is a gentler, slower form: once it touches the moisture on your teeth, it breaks down into hydrogen peroxide and urea. So both end up doing the same job.
Hydrogen peroxide is a small molecule. It passes through the enamel and into the dentine. There it releases very reactive forms of oxygen that break apart the large coloured molecules responsible for staining. Smaller molecules reflect less colour, so the tooth looks lighter. Nothing is scraped away, and the tooth is not painted. The colour change happens inside the tooth.
That is also why whitening has limits. Some stains break down easily, such as the general yellowing of age. Others, such as grey banding from certain antibiotics taken in childhood, or a dead tooth, respond slowly or only partly.
Whitening only works on natural tooth. Porcelain, zirconia, composite and denture acrylic do not contain the stain molecules peroxide breaks down, so crowns, veneers, fillings and dentures stay the same colour.
In-clinic whitening and home whitening
There are two main professional methods. The NHS and the Oral Health Foundation both describe them in similar terms.
In the dental chair
The dentist protects your gums with a soft shield or paste, then paints a stronger gel onto the teeth. Sometimes a light or laser is used alongside it. The appointment usually takes one to two hours, and you see a change the same day. Eye protection is given if a light is used.
At home with custom trays
The dentist takes a scan or impression and makes thin trays that fit your teeth closely. You put a small amount of weaker gel in the trays and wear them for a set time each day or overnight. The NHS describes this as usually taking two to six weeks. Because the trays fit closely, the gel stays on the teeth and away from the gums.
| In-clinic | Home trays | |
|---|---|---|
| Gel strength | Higher | Lower |
| Time | About 1 to 2 hours, one visit | About 2 to 6 weeks of wear |
| Control | Dentist applies and watches | You apply as instructed |
| Top-ups | Another appointment | Keep the trays and reuse |
| Fits a short trip | Yes | Started in clinic, finished at home |
Which is better? A 2016 systematic review in Operative Dentistry compared the two and found no overall difference in how white the teeth became or in the risk of sensitivity. In practice, people visiting us for a week often have in-clinic whitening, or start with trays made in Antalya and carry on at home.
Sensitivity: why it happens and what helps
The most common side effect is sensitivity, especially to cold. As peroxide passes through the enamel, it can briefly irritate the nerve inside the tooth. The NHS and the Oral Health Foundation both describe this as usually short-lived. Some people also get mild soreness of the gum if gel touches it.
Things that help:
- A toothpaste for sensitive teeth, used for a couple of weeks before and during treatment.
- Shorter or less frequent tray wear, if your dentist agrees.
- Avoiding very cold drinks for a day or two after an in-clinic session.
- Telling the dentist straight away if sensitivity is sharp or lasts.
If you already have exposed roots from gum recession, worn enamel or cracked teeth, sensitivity can be stronger. That is one reason a dentist should check your teeth before whitening.
Who whitening suits, and who it does not
Whitening tends to work well for people whose own teeth are healthy but have yellowed with age or darkened from tea and coffee.
It is not a good idea, or should wait, if you have:
- Untreated decay or gum disease. These should be treated first.
- Front crowns, veneers or large fillings that you do not plan to replace. They will stay the old colour while the teeth around them lighten.
- Very sensitive teeth or a lot of exposed root surface.
- A single dark tooth, which may need different treatment from the inside.
The NHS also says whitening is not done on anyone aged 17 or under.
Whitening before crowns or veneers
If you are planning new crowns or veneers on some teeth, whitening the rest first is often sensible. The new work is then made to match your whitened teeth, not your old shade. If you whiten afterwards, your natural teeth lighten and the crowns do not, which can leave a mismatch that only replacing the crowns will fix.
The colour after whitening also takes a little time to settle, so we plan the order of treatment and the shade-taking with that in mind. In a full makeover this is all written into your plan. See how many crowns a full smile needs and our smile makeover page.
Why it should be done by a dental professional
In the UK, the General Dental Council treats tooth whitening as dentistry, and the Oral Health Foundation states it must only be carried out by a registered dental professional or under a dentist’s prescription. The NHS warns that whitening in beauty salons, or with kits bought online, may not work as well and may harm teeth and gums. Over-the-counter strips and gels contain only a very small amount of whitening agent and mostly lift surface stains.
In Antalya, whitening at our clinic is done by our dentists after an examination, with the gums protected and written aftercare.
How long the result lasts
The NHS says whitening is not permanent but may last around three years if you follow your dentist’s advice. It fades faster with smoking and dark drinks. Good habits help it last:
- Rinse with water after tea, coffee or red wine.
- Brush twice a day with fluoride toothpaste.
- Keep regular hygiene visits to remove surface stains.
- Keep your trays and use them for short top-ups if advised.
Ask us whether whitening suits you
Send us a few clear photos of your smile in daylight, and tell us about any crowns, veneers or fillings at the front. A dentist will look at them and tell you in writing whether whitening is likely to help, which method suits your trip, and what it costs. We give a written price after seeing your photos. Use our contact form or message us on WhatsApp. You can also read more on our teeth whitening page.
Common questions
Does teeth whitening damage enamel?
When it is done or supervised by a dentist with proper products, whitening does not strip the enamel off. It works through the enamel. The common side effect is temporary sensitivity to cold. Unregulated products, or whitening done by people without dental training, can harm teeth and gums, which is why the NHS advises going through a dental professional.
How long does whitening last?
The NHS says the effect may last around three years if you follow your dentist’s advice. Tea, coffee, red wine and smoking bring staining back sooner. Home trays can be kept for occasional top-ups.
Will whitening change the colour of my crowns or veneers?
No. Whitening only works on natural teeth. If you whiten and have crowns at the front, they may look darker than the newly whitened teeth, and may need replacing to match.
Is whitening painful?
It is not painful for most people, but many feel some sensitivity, especially to cold, during and for a short time after treatment. It usually settles within a few days.
How much does whitening cost at your clinic?
We do not publish a single whitening price, because it depends on the method and what else you are having done. We give a written price after seeing your photos. See our teeth whitening page.
Sources
- NHS: Teeth whitening
- Oral Health Foundation: Tooth whitening
- General Dental Council: Considering tooth whitening? (PDF)
- de Geus et al. (2016), Operative Dentistry: at-home vs in-office bleaching, systematic review and meta-analysis
- Japanese Dental Science Review (2025): optimal carbamide peroxide concentration for at-home bleaching
Checked October 2026. Where we give our own view as a clinic, we say so.
Get your treatment plan and price in writing
Send a few photos of your teeth or a recent X-ray. One of our dentists looks at it and you get an itemised plan before you book anything.