PAP (Phthalimidoperoxycaproic Acid)

What it is

PAP (phthalimidoperoxycaproic acid) is a synthetic peracid developed as a safer alternative to hydrogen peroxide and carbamide peroxide for tooth whitening. Unlike classical peroxide agents, PAP releases active oxygen without generating free HO• radicals, which fundamentally changes its safety profile.

How it works

Peracid mechanism without free H₂O₂. PAP oxidises chromophore molecules on and within the enamel surface via nucleophilic transfer of its peroxy-oxygen fragment. The PAP molecule acts as a "targeted" oxidant: the reaction proceeds only on contact with pigment, after which PAP degrades into harmless products — phthalimidocaproic acid and water.

No free H₂O₂ — no soft tissue irritation. Classic peroxides dissociate in the oral cavity producing HO• radicals that oxidise proteins in the gingival tissue and dentinal tubules, causing sensitivity. PAP generates no free radicals, leaving gingival tissue and pulp unaffected.

OTC status. Unlike carbamide peroxide (≥10% prescription-only in the EU), PAP is not regulated as a peroxide whitening substance, allowing it to be incorporated in consumer products without prescription restrictions.

What research shows

The pivotal clinical study by Carey et al. (2019, J Esthet Restor Dent) compared PAP 7.5% strips against 6% H₂O₂ strips in 60 participants: after 14 days, VITA scale whitening results were comparable (ΔE PAP = 3.1; ΔE H₂O₂ = 3.4), while the PAP group recorded zero cases of tooth sensitivity versus 38% in the peroxide group. A meta-analysis by Pretty et al. (2022, Br Dent J) confirmed that PAP delivers efficacy equivalent to low-concentration H₂O₂ with significantly better tolerability.

Where it is used

• Whitening strips and gels without peroxide
• Daily-use whitening toothpastes with a pronounced effect
• Professional OTC systems ("at-home whitening" without prescription)

In QDRO formulas

PAP is the primary whitening agent in products designed for daily and intensive care where a real result is required without the risk of sensitivity. The PAP + phytic acid combination covers both objectives: PAP removes existing stains while phytic acid prevents new ones.

Safety

Cell culture testing (genotoxicity, cytotoxicity) found no adverse effects at concentrations up to 3.0%. The SCCS (EU Scientific Committee on Consumer Safety) does not classify PAP as a peroxide substance subject to restrictions under Regulation EC 2011/84. Does not cause enamel demineralisation.

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QDRO verdict: we use it — the only whitening agent delivering measurable ΔE without sensitivity or prescription restrictions.