If you've shopped for teeth whitening in the last decade, you've met hydrogen peroxide — the active in most strips, gels and in-chair treatments. It works. It also has a reputation: zingers, sensitive teeth, irritated gums. PAP is the newer name on the label, and the honest question is whether it's a real alternative or just marketing. Here's what the research actually says.
What the two actives do
Hydrogen peroxide whitens by oxidation — it breaks down stain molecules inside the tooth. Effective, well-studied, and the reason "professional whitening" works. The catch is that the same oxidative process can temporarily open up the tooth's surface and irritate the nerve, which is where the sensitivity stories come from.
PAP (phthalimidoperoxycaproic acid) also oxidises stain molecules — but through a different pathway that, in laboratory studies, doesn't produce the free radicals associated with enamel-surface etching. Same goal, gentler chemistry.
What the studies show
A 2025 systematic review in Dentistry Journal looked across the published in-vitro and clinical evidence on peroxide-free color correctors, including PAP. The short version: PAP-based formulas produce visible shade improvement, without the enamel-surface damage or sensitivity spikes associated with peroxide.
An in-vitro study comparing PAP directly against peroxides found the two essentially level on lightening effect — with the difference showing up in what happened to the enamel surface afterwards, in PAP's favour.
To be fair to peroxide: some studies still show it ahead on raw whitening power, especially at high concentrations. If you want the strongest possible effect and don't mind the sensitivity roulette, dentist-supervised peroxide remains the heavyweight option.
So which should you choose?
It depends on what you're optimising for. Peroxide at professional strength wins on speed. PAP wins on comfort — visible results without scheduling your coffee around zingers. For everyday whitening, especially if you've had sensitivity before, the peroxide-free route is the one you'll actually stick with.
That's the bet behind FLASH: PAP for the whitening, hydroxyapatite to support the enamel surface, potassium citrate to keep things calm — in a strip that dissolves in under 10 minutes. The full breakdown lives on our science page.
Statements refer to published research on the individual actives, not clinical trials of this product. Individual results may vary.