Teeth whitening: techniques, effectiveness and risks

Teeth whitening means making the shade of your teeth lighter with a product that works inside the enamel and the dentine (the layer under the enamel). Before you consider it, it helps to understand where the colour comes from: some stains come off with a simple clean, others do not, and some teeth do not whiten at all. This page sums up what reviews of the scientific literature say, cited in the text. It is here to inform you; it does not replace an examination: every mouth is different.

Why do teeth turn yellow?

The natural shade of teeth varies from one person to another: slightly yellow teeth are not necessarily unhealthy teeth. When the colour changes, there are two main families of stains (Viscio et al., 2000, PubMed).

External stains

They settle on the surface of the tooth, in the thin film that covers it. They come from pigments brought in from outside: tea, coffee and tobacco are common examples. They are the easiest to remove.

Internal stains

They are inside the structure of the tooth itself: a defect in how the enamel formed, fluorosis (too much fluoride while the teeth were forming), or certain antibiotics taken while the teeth were forming. They do not come off with brushing or with a clean at the dentist's.

A single tooth that darkens, for example after a knock or a root canal treatment, is a separate case. The dentist can sometimes lighten it from the inside, but how these teeth do in the long term has been little studied (Plotino et al., 2008, PubMed).

Scaling, polishing or teeth whitening: what is the difference?

There are two ways to make teeth look lighter: remove surface stains mechanically with a slightly abrasive product, or change the colour of the tooth chemically with a peroxide (Li, 2017, PubMed).

• Scaling removes tartar (hardened dental plaque) from the teeth and under the gum. It is first and foremost care for your gums.
• Polishing removes surface stains. The tooth gets its original colour back, but does not become lighter than it naturally is.
• Whitening uses a peroxide-based gel that lightens the shade of the tooth itself.

For teeth dulled by tea, coffee or tobacco, a scale followed by a polish is often enough. Whitening is only worth discussing after that, on clean and healthy teeth.

Teeth whitening techniques

In-chair whitening

The dentist applies a gel at the practice, after protecting your gums, in one or more sessions. The lamps and "lasers" that are often promoted are not necessary: a review of 28 studies found no type of light that improved the result compared with the same gel without light (Maran et al., 2019, PubMed). Another review reaches the same conclusion (SoutoMaior et al., 2018, PubMed).

At-home trays, supervised by your dentist

The dentist takes impressions and has custom-made trays produced. At home, you put a gel your dentist gives you into the trays, following their instructions, for a few weeks, with check-ups. A review of 32 studies comparing this method with in-chair whitening found similar effectiveness, with slightly less intense sensitivity at home; the quality of the evidence remains low (de Geus et al., 2025, PubMed). Two other reviews show that less concentrated gels cause less sensitivity for a similar result (Terra et al., 2025, PubMed; Cordeiro et al., 2025, PubMed). So the choice of product is up to your dentist, not to advertising.

Over-the-counter products

• "Whitening" toothpastes: a review of 14 trials shows they reduce surface stains better than an ordinary toothpaste, with studies that differ a lot from one another (Hajisadeghi et al., 2025, PubMed). They act mainly on external stains, and less than strips do (Naidu et al., 2020, PubMed).
• Whitening strips: a review of 37 studies (1,932 participants) found a short-term effect compared with a placebo, with few side effects, but low-quality evidence; its authors point out the risks of using them without professional follow-up (de Oliveira et al., 2024, PubMed). In the laboratory, strips without peroxide did not lighten teeth (Hul et al., 2026, PubMed).
• Activated charcoal: in a review of 11 laboratory studies, charcoal toothpastes whiten less than other products and are more abrasive (Tomás et al., 2022, PubMed). They can also make resin fillings rougher (Kim et al., 2025, PubMed).
• Purple colour correctors: they partly mask the yellow. A review of 6 studies, only one of them in patients, found a modest effect (Boruga et al., 2025, PubMed).

"Teeth whitening devices" and LED kits

Online, you can find kits with a standard tray and a small lamp. At the practice, light has not been shown to improve the result (see above): so there is nothing to suggest the lamp is what does the whitening. Any effect depends on the gel supplied, whose composition is not always clear. Show the product to your dentist before using it.

What studies say about effectiveness

The large Cochrane review of at-home whitening (71 trials) concludes that peroxide-based products lighten teeth compared with a placebo, over periods of 2 weeks to 6 months. But the certainty of the evidence is low to very low, and it is impossible to say which product, which concentration or which duration is best (Eachempati et al., 2018, PubMed).

In other words, whitening generally works, but the result varies from one person to another and cannot be promised in advance. Marked internal stains often respond less well.

Side effects: sensitivity, gums, enamel, fillings

• Tooth sensitivity is the most common effect: small twinges with cold, or spontaneous ones, during treatment. According to the Cochrane review, it is most often mild and temporary, and more common with concentrated products (Eachempati et al., 2018, PubMed). A review of 77 studies describes it as mild on average at home (Terra et al., 2025, PubMed).
• Gum irritation: redness or a burning feeling, usually temporary, when the gel touches the gum.
• Enamel: a review of laboratory studies found a small drop in enamel hardness, with no clearly important effect on the health of the tooth when protocols are followed; these are laboratory results (Márton et al., 2026, PubMed).
• Fillings, crowns and veneers do not change colour. After whitening, their shade may no longer match that of the neighbouring teeth (Miranda et al., 2025, PubMed); a visible filling sometimes has to be redone.
• Overuse: repeating treatments or going beyond the instructions increases the risks, a particular concern in teenagers (Lee et al., 2005, PubMed).

If sensitivity appears, tell your dentist: they can space out the applications or take a break.

Who should avoid or postpone whitening?

• Children and teenagers: a review points out that sensitivity or irritation can affect 1 patient in 2 or 3, and that the decision for a teenager is made case by case (Lee et al., 2005, PubMed).
• Pregnancy and breastfeeding: these women are excluded from studies (for example Moncada et al., 2013, PubMed). Without data, the safest choice is to postpone.
• Tooth decay, gum disease or teeth that are already sensitive: treat first, whiten afterwards.
• Crowns or veneers on the front teeth: they will not whiten, which can create a contrast (see the veneers guide).
• Ongoing braces: talk to the practitioner who follows your braces before using any whitening product.

How long does the result last?

Whitening is not permanent, but it can last. In a trial of 62 patients seen again four and a half years after in-chair whitening, the effect was still visible, with a slight return of colour (Hortkoff et al., 2025, PubMed). In another trial of 45 participants, the result of at-home trays held up after 2 years (Mailart et al., 2025, PubMed). These are small studies; how long it lasts also depends on your habits.

Keeping your teeth bright: prevention tips

• Brush your teeth twice a day with a fluoride toothpaste.
• After tea or coffee, rinse your mouth with water.
• Tobacco stains teeth: stopping also helps your gums.
• Have a scale and polish when your dentist recommends it.
• Avoid charcoal powders and acidic home remedies (lemon, vinegar), which wear down or attack enamel.
• A "whitening" toothpaste can help maintain the result; ask for advice if your teeth are sensitive.

In practice

1. Have your teeth examined first: the cause of the staining decides the solution.
2. Start with a scale and polish if your teeth are dull on the surface.
3. Have tooth decay and gum problems treated before any whitening.
4. Mention a pregnancy, breastfeeding, sensitive teeth or braces.
5. Choose whitening supervised by your dentist over kits bought online.
6. Follow the instructions and report any sensitivity or irritation.
7. Keep good habits to make the result last.

Frequently asked questions

Does teeth whitening damage enamel?

According to laboratory studies, the effect on enamel hardness is small when protocols are followed. The risk increases with overuse of products and with abrasive powders such as charcoal: follow the instructions and stay under supervision.

Does a teeth whitening device bought online work?

According to studies, strips containing a peroxide give a short-term effect, but products without peroxide seem to be ineffective, and the lamp in LED kits has not been shown to be useful. Show the product to your dentist before using it.

Is whitening painful?

Tooth sensitivity is common during treatment, most often mild and temporary. Tell your dentist about it: they can adjust the pace or take a break.

Why did my yellow teeth not get whiter after a scale and polish?

Scaling and polishing remove tartar and surface stains, but they do not change the tooth's own colour. If the shade comes from inside, only whitening or another solution discussed at the examination can lighten it.

How much does teeth whitening cost?

It depends on the technique and the number of sessions, and each practitioner sets their own fees. Ask for the full cost before you start, after the examination.