Is teeth whitening safe? What works and how long it lasts

Is teeth whitening safe, and does it work? Both depend largely on the method, and not every whitening product is effective. Whitening toothpastes mostly remove surface stains, over-the-counter strips sold in the EU contain very little peroxide, and there is no evidence that home remedies whiten teeth. What changes the natural colour of your teeth is a peroxide gel, used after a dental examination, either at the dentist or at home with custom-made trays.

Why do teeth turn yellow?

Stains can sit on the surface of a tooth or inside it:

• Surface stains. These are left by coffee, tea, red wine, cola, dark fruit and tobacco. They can often be removed with a scale and polish (teeth cleaning) alone.
• Stains inside the tooth. These lie in the enamel or in the dentine underneath. Age is a common cause: over the years, enamel becomes thinner and more translucent, so more of the yellowish dentine shows through.
• Other causes of internal discolouration. These include certain antibiotics (tetracyclines) or too much fluoride (fluorosis) while the teeth are still developing, as well as a knock to the tooth, after which the nerve (pulp) may bleed or die.

Whitening works on stains inside the tooth, but not equally well for everyone. Yellowish teeth usually respond well, and brownish teeth somewhat less well.

Grey teeth, and discolouration caused by medicines or an injury, may lighten only partly, only after longer treatment, or not at all. White marks usually respond less well than brown stains. That is why an exact shade cannot be promised in advance.

How teeth whitening gel works

Teeth whitening, also known as teeth bleaching, uses a gel containing hydrogen peroxide or carbamide peroxide (which releases hydrogen peroxide). The peroxide passes into the enamel and dentine and breaks down the coloured molecules that cause staining. Nothing is drilled or removed from the tooth.

Whitening only changes the colour of natural teeth. Fillings, crowns (caps), veneers and dentures keep their colour, so if you have any of these on your front teeth, they may stand out after whitening.

Which teeth whitening methods work, and which don’t?

Teeth whitening at the dentist

The dentist protects your gums with a special barrier and applies the gel to your teeth. Sometimes a light or laser is also shone on the gel; this is often called laser teeth whitening. According to the UK’s NHS, whitening at the dentist usually takes a single visit of one to two hours.

Teeth whitening at home with trays from your dentist

Thin trays are custom-made to fit your teeth. You fill them with gel and wear them as instructed, usually for one to six weeks. Under EU rules, the first application in each course of treatment is carried out by the dentist or under their direct supervision.

Whitening at the dentist and at home can also be combined. A 2018 Cochrane review (71 studies, 3,780 adults) found that home whitening gels lightened teeth more than a placebo. However, the evidence was of low to very low certainty, and no single product, concentration or treatment schedule was shown to be clearly better than the others.

Whitening strips and over-the-counter gels

Under EU rules, as interpreted by the Council of European Dentists, products sold over the counter may contain no more than 0.1% hydrogen peroxide. Gels with more than 0.1% and up to 6% may be sold only to dentists, and anything above 6% is not permitted for cosmetic whitening.

Whitening toothpaste, activated charcoal and home remedies

Does whitening toothpaste work? Only on surface stains. Whitening toothpastes mainly contain fine abrasive particles that polish these stains away. Your teeth may look cleaner, but their natural colour does not change.

According to the American Dental Association (ADA), there is no evidence that popular home remedies whiten teeth, and some may do harm:

• Activated charcoal: no evidence that it changes tooth colour; in studies, it was abrasive enough to wear away enamel.
• Strawberries with bicarbonate of soda (baking soda): no measurable whitening in one study.
• Oil pulling (swishing oil around the mouth): no whitening effect was found.

Beauty salon whitening and kits bought online

The NHS warns that whitening in beauty salons and products from unverified sellers do not work as well as whitening by a dentist, and may harm your teeth and gums. The UK’s Oral Health Foundation also reports cases of permanent damage after such treatments.

Is teeth whitening safe?

When whitening is supervised by a dentist after an examination, and the gel is used as instructed, studies mostly report mild, temporary side effects, although the evidence is not very strong:

• Tooth sensitivity to cold or sweet food and drink. This is the most common side effect: up to about two in three people who whiten with trays have mild to moderate, temporary sensitivity. It can start within the first few days. Tooth sensitivity after whitening usually settles within a few days of finishing treatment.
• Gum irritation, such as a burning feeling or white patches, if the gel touches the gums. This usually passes.
• Changes to the enamel. Whitening may change the surface roughness of the enamel, and for a time composite and ceramic may not bond as well to the tooth. That is why new white fillings or bonding are done some time after whitening.

More is not better. A stronger gel is more likely to cause sensitivity and will not necessarily make your teeth whiter. Use the gel only as your dentist advises: overuse can damage enamel and gums.

According to a 2022 systematic review cited by the ADA, hydrogen peroxide whitening products do not appear to cause cancer of the lining of the mouth.

When to wait before whitening

It is better to hold off if:

• you are under 18: in the EU, professional whitening gels are not used on anyone under that age
• you are pregnant or breastfeeding (see our article Dental care in pregnancy)
• you have tooth decay, inflamed gums, or fillings that are cracked or leaking: these need treating first
• your teeth are very sensitive, or you are allergic to any of the ingredients in the gel

How long does teeth whitening last?

Teeth whitening is not permanent. According to the NHS, the effect may last around three years if you follow your dentist’s advice. The Oral Health Foundation says results can last several years, but this varies from person to person. Long-term evidence is limited: the studies in the Cochrane review lasted no more than six months.

Smoking, coffee, tea and red wine bring staining back sooner. To help your result last:

• Cut down on coffee, tea, red wine and tobacco.
• Brush twice a day with fluoride toothpaste; see how to brush your teeth properly.
• Keep up your regular check-ups and professional cleaning.
• Keep your whitening trays, and ask your dentist when, and for how long, to use them for a top-up.
• Do not top up the colour yourself with stronger products bought online.

When to see a dentist

Book an examination:

• Before any whitening treatment. An examination shows whether your teeth and gums are healthy and what is causing the discolouration. In the EU, this is required before a professional gel is first used.
• If only one tooth has darkened, especially after a knock. The cause may lie in the nerve, so the tooth should be checked. If it has had root canal treatment, it can sometimes be whitened from the inside (internal bleaching), with a rare risk of the tooth breaking down near the gumline (resorption). Read more about root canal treatment.
• If sensitivity or gum irritation bothers you, or does not settle once you stop whitening.
• If you have visible fillings, crowns or veneers on your front teeth, so you can plan whether they will need replacing. Our page on white fillings and composite bonding and the article Veneers vs composite bonding vs crowns: how to choose may help.
• If your teeth are grey or the stains do not respond to whitening. Depending on the cause, options include microabrasion (removing a very thin layer of enamel) for shallow marks, bonding, veneers or crowns. Crowns, and often veneers, mean permanently filing down part of the tooth.

Our teeth whitening page explains the treatment step by step.

Teeth whitening: frequently asked questions

If you are thinking about teeth whitening, start with an examination: book an appointment and we can decide together whether whitening is right for you.