How does whitening act on the tooth?
Whitening gels contain hydrogen peroxide or carbamide peroxide. According to the American Dental Association (ADA), carbamide peroxide releases about one third of its content as hydrogen peroxide. The hydrogen peroxide penetrates enamel and dentine and oxidises the molecules that give the tooth its colour, so the tooth looks lighter. The ADA notes that it can reach the pulp, the inside of the tooth, within 15 minutes; this passage is linked to the sensitivity felt during and after whitening.
External stains from coffee, tea or tobacco, by contrast, can often be reduced with a professional cleaning alone. How long the result of whitening lasts is answered in our guide how long does teeth whitening last; this page is about whether and when whitening does harm.
Does whitening attack the enamel?
According to current knowledge, supervised whitening causes no clinically significant damage to enamel; the research is, however, inconsistent and consists mostly of laboratory studies. The ADA notes that some research suggests bleaching may alter the surface roughness of enamel.
The systematic review by Gkavela and colleagues (2024) sums up the position: individual laboratory studies measured changes in enamel hardness, more roughness and mineral loss, others did not; the results are contradictory. For whitening with carbamide peroxide, the authors see no clinically significant change in enamel structure. At the same time they rate the risk of bias in most studies as high, because the methods differ widely.
The Oral Health Foundation describes professional whitening as the safest and most effective route, with the dental team checking first that teeth and gums are healthy. In practice: after an examination, with a suitable product and for the set duration and frequency, no relevant enamel damage is to be expected; longer or more frequent use can raise the risk.
Which side effects are common?
The most common side effects are sensitivity and irritated gums, both usually temporary:
- Sensitive teeth: according to the ADA, up to two thirds of users can be affected by mild to moderate, transient sensitivity early in treatment; the concentration of the gel, the exposure time and the use of light influence the risk. The NHS lists sensitivity to cold or sweet food and drink among the effects, which may last a short time.
- Gums and mucosa: according to the ADA, irritation is usually caused by poorly fitting trays or an improperly applied protective barrier or gel; the NHS names sore gums or throat and white patches on the gums. In the practice, the gums are protected before the gel is applied, according to the Oral Health Foundation and MouthHealthy.
Concentration plays a role: in the systematic review by de Geus and colleagues (2018), sensitivity with ten percent carbamide peroxide was less frequent and milder than with stronger gels, with the same whitening result. What helps with sensitive teeth after whitening is explained in teeth whitening aftercare; for lasting sensitivity unrelated to whitening, see sensitive teeth.
When can whitening actually do harm?
Whitening does harm above all when teeth and gums are not healthy or the product is used without supervision:
| Situation | What the sources say |
|---|---|
| Decay, leaking fillings or unhealthy gums | The NHS says whitening is not done if your teeth or gums are unhealthy; your dentist should check them first and treat problems beforehand |
| Sensitivity from peroxide reaching the nerve | According to MouthHealthy, peroxide can pass through the enamel to the dentine and irritate the nerve; treatment can be paused and tried again later |
| Under 18 | The NHS does not offer whitening to people aged 17 or younger; according to the CED, the EU Cosmetics Regulation prohibits products with more than 0.1 and up to 6 percent hydrogen peroxide for under-18s |
| Pregnancy and breastfeeding | The NHS does not recommend whitening while pregnant or breastfeeding |
| Overuse | According to MouthHealthy, overuse of whiteners can damage the tooth enamel or gums |
| Crowns, fillings and veneers | They do not lighten (NHS, Oral Health Foundation) and may need replacing afterwards to match |
This is why every whitening treatment starts with an examination, which also covers existing fillings and crowns, because they keep their colour.
Which rules apply to whitening products in Europe?
In the EU, according to the Council of European Dentists (CED), the Cosmetics Regulation prohibits the use of whitening products with more than 0.1 and up to 6 percent hydrogen peroxide on anyone under 18. The General Dental Council (GDC), the UK dental regulator, describes the same thresholds in practice: products releasing 0.1 to 6 percent may only be sold to dental practitioners, an appropriate clinical examination must take place beforehand, the first use of each cycle can only be carried out by a dentist or under their direct supervision, and products above 6 percent are prohibited for cosmetic use. According to the GDC, people who are not registered dental professionals are not entitled to provide tooth whitening.
What distinguishes in-office whitening, home whitening and free-sale products?
| Feature | In the practice (in-office) | Home whitening with trays | Free-sale products |
|---|---|---|---|
| Where? | In the dental chair | At home with custom-made trays | At home with strips, gel or toothpaste |
| Gum protection | Gel or rubber shield applied beforehand (MouthHealthy) | Custom-fitted tray, fit checked by the dentist | Left to the user |
| Duration | Usually about an hour (Oral Health Foundation); one or more sessions | 1 to 2 weeks (Oral Health Foundation) or 2 to 6 weeks (NHS) | Depends on the product |
| Supervision | Continuous | Check-up appointments | Usually none |
The information on home whitening is general; at our clinic whitening is carried out only in the practice. The ADA reports from a comparative study that an over-the-counter product took 16 days to reach the whitening achieved by a seven-day tray system. The NHS warns that kits from a pharmacy or online do not work as well and may harm your teeth and gums.
Why are beauty salons and home remedies risky?
Outside dentistry, the examination is missing: decay, gum disease and the cause of the discolouration go unrecognised. According to the NHS, whitening in beauty salons is less effective and can harm your teeth and gums; the Oral Health Foundation says untrained whitening can permanently damage teeth and gums.
“Natural” methods are not harmless either:
- Lemon and acids: according to the Oral Health Foundation, citrus fruits are among the acids that dissolve enamel (erosion). As the enamel thins, the yellower dentine shows through, teeth look more yellow and become sensitive.
- Baking soda and strawberries: a laboratory study cited by the ADA found no measurable whitening with this mixture.
- Activated charcoal: according to the ADA, there is insufficient evidence that charcoal products whiten effectively and safely.
What to bear in mind in the first days after whitening is described in teeth whitening aftercare.
What does this mean for whitening in Türkiye?
At our clinic in Serdivan, whitening is carried out only in the practice (in-office), not with trays at home. For you this has two consequences: the whitening is completed within your stay, and every application takes place under a dentist’s supervision with the gums protected. Beforehand we examine your teeth and gums, existing fillings and crowns and the cause of the discolouration; decay or gum inflammation is treated first. Plaque and external stains are removed in advance, also with a device that sprays a mixture of air, water and fine powder onto the tooth surface; some teeth already look brighter after this.
If fillings, crowns or veneers on the front teeth are to be matched to the new shade, we include them in the plan; we work with digital smile design. More on our teeth whitening and smile makeover pages. Before treatment begins you receive a written treatment and cost plan; the cost is confirmed after the examination. For a preliminary assessment, send us photos on WhatsApp at +90 532 363 49 54. How a stay with us works is described on our dental treatment in Türkiye page.