What does whitening do to a tooth?
The whitening gel (hydrogen or carbamide peroxide) passes through the tooth surface and breaks down the particles that cause discolouration using oxygen. It does not abrade or thin the enamel; it lightens the colour without changing the structure of the tooth. When used under a dentist’s supervision and at an appropriate concentration, it has not been shown to cause lasting damage to enamel.
The conditions in that sentence matter: under a dentist’s supervision and at an appropriate concentration. Almost every story of harm comes from situations where these two conditions were not met.
Why does sensitivity happen, and how long does it last?
During and after whitening there may be temporary sensitivity to cold. The cause is the gel briefly stimulating the inner tissue of the tooth — not loss of enamel.
- For most people it settles on its own within 24–72 hours.
- For those prone to sensitivity, the method is planned accordingly (home whitening, lower concentration, shorter sessions) and supported with desensitising gels and toothpastes.
- Many clinical studies have shown that blue-light and laser devices add nothing to the whitening result; for that reason we do not use them in our clinic.
- If sensitivity lasts more than a few days or is concentrated in a single tooth, there may be decay, a crack or gum recession underneath — a check-up is needed.
The real risks: uncontrolled products
The problem with products bought from pharmacies and online is not their active ingredients but that they are used without an examination and without measure.
- Charcoal powder and “whitening” abrasive toothpastes: they do not lighten the colour; they abrade the enamel surface. Over time the yellower dentine underneath shows through more — so the teeth start to look darker.
- Strips, pens and ready-made tray gels: the gel spills onto the gums, causing gum burns and irritation. Because the same tray and the same concentration are applied to everyone, sensitivity cannot be controlled.
- “Natural” methods such as lemon, baking soda or vinegar: their acidic and abrasive effect thins the enamel irreversibly.
- Repeating too often: after whitening, the shade is maintained for roughly 1–2.5 years depending on diet and care. Repeating it every few months to get “even whiter” strains the tooth unnecessarily; a natural, balanced shade is the aim.
Who should not have whitening?
Most of the cases where whitening is called “harmful” are in fact cases where it was applied to the wrong candidate. In the following situations, either we wait or a different route is chosen:
- Active decay, a fracture or a leaking filling — these are treated first; otherwise the gel reaches the inside of the tooth and causes pain.
- Gum inflammation and bleeding — gum health first; whitening is left until afterwards.
- Pregnancy and breastfeeding — although there is no evidence of harm, it is postponed as a precaution.
- Severe sensitivity / exposed root surfaces — the sensitivity is addressed first.
- Fillings, veneers and crowns — whitening does not change their colour; after the procedure, older restorations at the front may need to be renewed to match the new shade. This is a decision to discuss beforehand.
- Discolouration from inside the tooth (medication, trauma, developmental) — whitening alone may not be enough; in that case tooth-specific (internal) whitening or a restorative option is considered.
A conservative view: diagnosis first, then the least intervention
“Forcing whitening on a tooth whose colour will not lift is the same mistake as recommending a crown for a tooth that whitening would solve: the wrong tool.”
The right order is this: the cause of the discolouration is identified, tooth and gum health are checked, a cleaning is done first if needed, and then the method that suits the person is chosen. For discolouration caused by external factors, teeth whitening is usually sufficient on its own and the most conservative solution. You can find the check-up and scaling process before whitening on the preventive dentistry page. No whitening is permanent; but in the right candidate, with the right method and good care, it is maintained for a long time.
