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Whitening agents

Hydrogen peroxide

Also listed as H2O2, peroxide, carbamide peroxide (releases hydrogen peroxide)

The only ingredient that actually bleaches teeth lighter. Works in strips and trays; in toothpaste and rinses contact time is too short to do much.

Moderate evidenceTypical strength: Freely sold EU oral products at most 0.1%; US over-the-counter strips often around 6-10%, sometimes higher

What it is

Hydrogen peroxide diffuses into enamel and dentine and breaks down the pigment molecules that make teeth look yellow. It changes the tooth's own colour, unlike abrasives, which only remove surface stain. Carbamide peroxide releases roughly a third of its weight as hydrogen peroxide.

Results depend on strength and contact time. Strips and trays hold gel on teeth for 30 minutes or more; a toothpaste or mouthwash is rinsed off within minutes. In the EU, products sold freely may contain at most 0.1% hydrogen peroxide; 0.1-6% is dentist-supervised only and not for under-18s.

How strong is the evidence?

Moderate evidence

A Cochrane review found home peroxide strips and tray gels whiten teeth versus placebo, with stronger products working better. All included trials were manufacturer-sponsored, short-term and mostly at high risk of bias, and long-term harms have not been studied well. Evidence for low-level peroxide in toothpaste and rinses is thinner.

What it's used for, checked

Whitens teeth (strips, trays)

Holds up

Effective over about 2 weeks; results fade over months.

Whitens teeth (toothpaste, mouthwash)

Mixed

Low strength and short contact; any visible effect is small and slow.

Whitens crowns, veneers or fillings

False

Restorations do not bleach, so a mismatch can appear.

Who should be careful

  • Tooth sensitivity and gum irritation are common and usually settle after stopping; a potassium nitrate or stannous fluoride paste can help.
  • Get a dental check before whitening: bleaching over untreated decay or gum disease can hurt and mask problems.
  • Not for children or teenagers (EU rules bar products above 0.1% for under-18s), or during pregnancy as a precaution.
  • Do not swallow whitening gels or rinses; keep them away from children.

The studies

Every citation is checked against its PubMed record.

  1. Home-based chemically-induced whitening of teeth in adults.
    Hasson H, Ismail AI, Neiva G · Cochrane Database Syst Rev · 2006 · Systematic review

    25 short-term trials, all manufacturer-sponsored and mostly at high risk of bias: peroxide strips and tray gels whiten teeth versus placebo, with differences driven by peroxide strength. Mild-to-moderate tooth sensitivity and gum irritation were the common side effects.