Tooth Whitening. What It Actually Is

A toothpaste labelled "whitening" doesn't whiten. It polishes.

That's not a semantic quibble — these are different mechanisms with different outcomes.

How polishing works

A tooth is covered by a thin organic film called the pellicle. Pigments settle onto it: coffee, tea, red wine, food dyes. These are extrinsic stains — they sit on the outside, on the surface.

Abrasives in toothpaste — fine particles of silica or calcium carbonate — scrub away this film along with the stains. The tooth looks cleaner. That's what most pastes call "whitening."

No toothpaste changes the actual colour of a tooth. This is confirmed by a 2024 meta-analysis (PMC12010553): whitening toothpastes act only on extrinsic deposits — not on intrinsic colour.

Abrasive hardness is measured in RDA units. Most "whitening" toothpastes sit at 100–200 RDA. The ISO safe limit for lifelong use is 250. The higher the RDA, the more intensive the polishing — and the faster the enamel wears.

Real whitening: what happens inside

The actual colour of a tooth doesn't come from enamel. Enamel is semi-transparent. Colour comes from dentine beneath it — a yellowish tissue that shows through the enamel layer.

Chromogens accumulate in dentine and in the organic matrix of enamel — molecules with conjugated double-bond systems that absorb light and produce a darker hue.

Hydrogen peroxide (H₂O₂) penetrates through the enamel into the tooth. Inside, it breaks down into reactive oxygen species that attack the double bonds in chromogens. The molecules are destroyed, stop absorbing light. The tooth brightens from within.

This is chemistry, not mechanics.

Why professional whitening is aggressive

In-office systems use 15–35% H₂O₂ activated by light. The effect is fast — 40–60 minutes.

The cost: stress on the pulp.

At concentrations of 30–35%, peroxide has been detected in the pulp chamber — confirmed by direct measurements on isolated teeth (PMC7087340). Pulp cells can't neutralise the free radicals fast enough through their own enzymatic systems (catalases, peroxidases) — they become overwhelmed.

Sensitivity after in-office whitening: 67–78% of patients. Enamel demineralisation, mucosal irritation, transient pulp inflammation — all documented in systematic reviews.

The EU Cosmetics Directive 2011/84/EU caps H₂O₂ in cosmetic products at 6%. Above that — dentist-supervised only. The reason is exactly these risks.

Home whitening: a different logic

At concentrations of 3–10% H₂O₂ (or 10–16% carbamide peroxide, which slowly releases peroxide), the process is extended over time.

The pulp keeps pace. Enzymes neutralise radicals before critical load accumulates.

A 2018 meta-analysis (PubMed 29949477): with 10% carbamide peroxide, the risk of sensitivity is nearly half that of high concentrations (OR = 0.41). The final result is comparable.

Slower doesn't mean weaker. It means the tooth isn't under stress.

Natural tooth colour is yellow

Nobody is born with white teeth.

Dentists classify natural tooth shades into four groups: reddish-brown, reddish-yellow, grey, and reddish-grey. None of them is white.

With age, enamel thins from chewing and acid exposure. Dentine builds up a secondary layer. Teeth become visually more yellow — this is physiology, not pathology.

Whitening restores brightness: it removes accumulated chromogens that shouldn't have been there. But making a tooth "whiter than nature intended" means bleaching the organic matrix of the enamel too. The result: a flat, lifeless, chalky shade. Dentists call this "opalescing" — a sign of structural damage.

What this means in practice

If a toothpaste promises "whitening" — ask what exactly it does. Removing surface stains: honest. Whitening from within: no.

If you want a real result, you need peroxide. But concentration and application logic matter: gradual, with remineralisation between courses.

Bright teeth are an achievable goal. Nuclear-white is damage.

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Sources: Carey, 2014 (PMC4058574) · Llena et al., 2018 (PMC6165410) · PubMed 29949477 · PMC7087340 · EU Directive 2011/84/EU · ADA Oral Health Topics: Whitening