Hydrogen Peroxide

A €2 bottle of pharmacy peroxide and a €150 professional bleaching gel contain the same active ingredient. The only difference is concentration. But that difference determines whether you whiten your teeth or damage your pulp.

How whitening works

Hydrogen peroxide is an oxidiser with a molecular weight of just 34 g/mol. The molecule is small enough to diffuse freely through enamel and dentine. This is the entire basis of the mechanism.

When H₂O₂ contacts organic pigments inside enamel, it breaks down into reactive oxygen radicals. These oxidise chromogenic compounds — long molecules that absorb visible light. The chains are cleaved, pigments are decolourised.

The effect targets intrinsic pigments within enamel, not surface staining. This is why hydrogen peroxide is the only agent with a proven mechanism for addressing true tooth yellowing — no abrasive or enzyme can replicate it.

"Hydrogen peroxide remains the most effective agent for whitening intrinsic pigments. No abrasive or enzyme can reproduce this mechanism."

— Carey CM, J Evid Based Dent Pract, 2014

Concentrations: from pharmacy shelf to dental chair

The market range spans from 0.1% in consumer products to 40% in professional office systems. This is not simply "weaker or stronger" — these are fundamentally different application regimes.

| Concentration | Application | EU status | |---|---|---| | Up to 0.1% | Consumer products: strips, toothpastes, rinses | No restrictions | | 0.1–6% | Home systems (trays, pharmacy strips) | Via dentist only | | 6–35% | Professional in-office whitening | Clinic only, dentist-supervised | | Above 35% | Industrial use | Prohibited in cosmetics |

EU Council Directive 2011/84/EU established a clear boundary: products containing more than 0.1% H₂O₂ cannot be sold directly to consumers. The first application cycle must take place at a dentist's practice; subsequent home use is permitted under their supervision.

This is not overcaution. There is concrete physiology behind it.

Why concentration is critical

Hydrogen peroxide molecules diffuse through enamel and dentine into the pulp. The rate of penetration is directly proportional to concentration.

At 35% H₂O₂, the compound is detectable in the pulp chamber within 15 minutes of application. Reactive oxygen species cause pulp inflammation, reduce cellular metabolism, and can lead to tissue necrosis with prolonged exposure (Bortolatto et al., 2020, PMC7087340).

At 1.5–3%, penetration occurs but pulp concentrations remain below the threshold for toxic effect. This is the range where whitening is achieved without structural damage.

A study by Marchiori et al. (2022, PMC10240089) found that in-office gels above 25% caused an inflammatory pulp response in the majority of patients even after a single 45-minute application.

Tooth sensitivity is the most common side effect. It does not arise because peroxide "irritates enamel." It directly irritates pulp nerve endings.

Hydrogen peroxide vs carbamide peroxide

Both appear on whitening product labels. They are not synonyms — they are different compounds with different kinetics.

Carbamide peroxide is a complex of H₂O₂ with urea. In contact with saliva it slowly decomposes: 10% carbamide peroxide releases approximately 3.5% H₂O₂.

| Parameter | H₂O₂ | Carbamide peroxide | |---|---|---| | Active agent | Direct | Released on decomposition | | Speed of action | Fast | Slower | | Effective equivalence | 3% H₂O₂ ≈ 10% carbamide | | | Formulation stability | Lower | Higher | | Typical products | Strips, in-office gels | Home tray systems |

Clinical efficacy is comparable at equivalent active H₂O₂ concentrations — no statistically significant difference (Tredwin CJ et al., 2006, PMID 16607324).

What this means in practice

Consumer products with hydrogen peroxide up to 0.1% are legal and safe when used correctly. The whitening effect at this concentration is moderate: visible with regular use in the absence of heavy staining.

Higher-concentration products require dental supervision — not because "the law says so," but because the risks are real and depend on enamel thickness, existing defects, and hidden cracks.

DIY approaches — applying pharmacy-grade 3% peroxide directly to teeth — work exactly as described: you will get a short-term whitening effect. Diffusion into the pulp will also occur.

In v.daily products (strips), H₂O₂ concentration complies with EU regulation. The effect is cumulative, without pain sensitivity during regular use.

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Sources: Bortolatto JF et al. (2020) PMC7087340 · Carey CM (2014) PMID 24929596 · Marchiori D et al. (2022) PMC10240089 · Tredwin CJ et al. (2006) PMID 16607324 · Soeteman GD et al. (2024) PMID 39030259 · EU Council Directive 2011/84/EU