Your Guide To PAP Teeth Whitening – Facts & Fiction

Written, Edited, and Reviewed by Dr David Chen.

Recently, a new teeth whitening product called PAP (phthalimidoperoxycaproic acid) has emerged onto the market. The claims are that it is peroxide-free but it can whiten your teeth more effectively than peroxide based products while doing it in a safer manner.

Hsmile VIO405 teeth whitening kit

The creator of this new product is hismile and as far as we know, they’re the first movers in this brand new market. It surely sounds amazing but are all those claims true or is it all fluff? We’ve done the research so sit back and take it all in.

Can PAP whiten your teeth?

PAP can whiten your teeth because it does possess the ability to oxidize stain molecules (chromogens). That process is similar to hydrogen peroxide but it works in a slightly different way because it doesn’t produce free radicals in the process.

We’ve found two studies which demonstrated the whitening effect of PAP:

So, can it make your teeth whiter? Yes, phthalimidoperoxycaproic acid products can whiten your teeth.

Note: Just for your information, the first study with the fantastic results does have a conflict of interest. The research paper was done by the creators of Hismile PAP+. Take note of the research and development team’s names and the paper’s authors.

How effective is it?

The efficacy of PAP teeth whitening has mixed results because there were other studies which found that it wasn’t as effective as hydrogen peroxide.

Studies which showed PAP to be inferior to HP:

In regards to phthalimidoperoxycaproic acid being ineffective for red wine and tea stains, the theory was that it had to do with its affinity to molecular polarity.

  • PAP seems to work better against low polarity stains.
  • It doesn’t work so well for high polarity stains.

Nonetheless, the gist of it is that there were some studies which said it worked and other studies where it said it didn’t do so well. You can give it a try and see if it works for you.

How long do results last?

Since phthalimidoperoxycaproic acid is still a fairly new product, there were literally only 5-6 scientific studies that were available about it. It hasn’t been around long enough to have had enough research done on it to show how long the whitening results last.

However, based on what we know about teeth whitening, the how long it lasts would be dependent on your lifestyle habits. The more staining foods and drinks you have, the faster your teeth will restain. The less of it you intake, the longer your whitened teeth should stay.

Where do I buy it?

Hismile makes PAP+ whitening products and they currently have two of them.

  • PAP+ teeth whitening strips
  • Whitening kit which includes the gel as well as a LED light tray
Hismile pap+ whitening strips

Whitening mechanism

PAP will whiten your teeth by oxidizing stain molecules and decolorize them. However, it is able to achieve this without the use of free radicals such as ROS (reactive oxygen species).

Instead of free radicals, it oxidizes the conjugated double bonds of chromogens via expoxidation.

  • PAP converts the carbon-carbon double bond into an epoxide.
  • Epoxides look distinctively like a triangle on molecular formulas.
  • End result is that the double bond has been converted to a single bond.
Credit: Mauro Pascolutti and Dileusa de Oliveira

The loss of the double bond is what causes the stain molecules to appear whiter.

  • The more double bonds a molecule has, the more light it absorbs and consequently the darker the it will appear to our eyes.
  • On the contrary, the less double bonds it has, the less light it absorbs and the “whiter” the molecule will look.

The image below shows the degree of color in relation to the amount of double bonds.

Degree of conjugation and their color for different compounds
Credit: UMass

Technically, the stain molecule is still there but it just becomes invisible to our eyes.

Vs Hydrogen Peroxide

The teeth whitening or oxidation mechanism for hydrogen peroxide works differently than PAP. Products with HP will oxidize the stain molecules by using the free radicals, hydroxyl (HO)• and perhydroxyl (HO2)•.

Hydrogen peroxide oxidation of double bonds
Credit: Clifton Carey

The overall end result is still the same.

  • HP converts the conjugated double bonds to single bonds.
  • Stain molecule now absorbs less light and thus appears lighter in color.

Safe or harmful?

Despite the mixed whitening results, most studies came to the same conclusion that use of PAP is safer when compared to HP.

Safer characteristic profile:

  • Less teeth sensitivity
  • Minimal gum irritation
  • No burning sensation
  • No surface changes to enamel

Basically, whitening with phthalimidoperoxycaproic acid can eliminate or reduce all of the adverse side effects that you get with peroxide. What makes it even safer is that most PAP whitening products actually have hydroxyapatite added to it. This new product is denoted by a plus symbol as a suffix, PAP+.

What that means is that this whitening gel will whiten your teeth and help remineralize it afterwards since that is what hydroxyapatite does. It is a remineralizing agent for enamel.

Is PAP truly peroxide-free?

Overall, PAP seems like a worthwhile teeth whitening agent to try due to all of its claims but we’ve always felt that it wasn’t truly peroxide free. It is marketed as a peroxide free whitening agent but is it really?

A little bit of research shows that PubChem classifies PAP as a part of the peroxide family. The most interesting part of this is that PAP, is a synthetic organic peroxy acid which is derived from caprolactam and phthalic anhydride. The peroxy acid is made by adding sulfuric acid to hydrogen peroxide.

In summary, it is made from hydrogen peroxide. So, what do you think about that?!


PAP teeth whitening has the potential to whiten your teeth just like peroxide does but it doesn’t come with all of the adverse side effects. Based on the chemistry of its whitening mechanism, the theory seems solid.

We would recommend to give these products a try and see how it goes. If it works then that’s great. If it doesn’t work as well as HP, at least now you know. You won’t know how your mouth reacts until you use it. Just make sure you’re not allergic to it…


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