top of page

How DOES Hydrogen Peroxide Actually Whiten Teeth?

Updated: Jan 30

Hydrogen peroxide whitens teeth by forming free radicals that oxidize stains as it diffuses through each layer of the tooth. However, stain oxidation does not physically remove it from the tooth structure. Peroxide is used in most OTC and professional teeth whitening products.

16% peroxide KoR whitening
16% peroxide

Hydrogen peroxide whitening mechanism overview:

Hydrogen peroxide forms free radicals

Hydrogen peroxide in its natural state does not whiten teeth because the true whitening agents are the free radicals that are formed upon its decomposition. The free radicals are highly reactive and are the ones which initiate oxidation of the tooth stains.

Decomposition of hydrogen peroxide

Hydrogen peroxide is naturally very unstable and will readily decompose into the final products of water (H2O) and oxygen (O2).

Hydrogen peroxide decomposition reaction
Hydrogen peroxide decomposition reaction

However, the intermediary steps results in the formation of powerful oxidizing free radicals, hydroxyl and perhydroxyl.

Hydrogen peroxide free radical formation mechanism
Hydrogen peroxide free radical formation mechanism

To be crystal clear, the hydrogen peroxide itself does not react with the stains in teeth but rather it is the free radicals that do. Therefore, it is upon the decomposition of peroxide which creates the free radicals that actually whiten your teeth.

Whitening gel diffuses through tooth

The hydrogen peroxide free radicals, hydroxyl and perhydroxyl, are potent enough to diffuse through each and every layer of the tooth.

Yes, that means it can penetrate through the enamel and reach the dentin. As a matter of fact, studies have shown that after about 15 minutes you can find the whitening gel at the pulp chamber or nerve of the tooth.

tooth anatomy
Every layer of a tooth

That is literally how powerful these oxidizing free radicals are.

This should also answer two questions that you probably have on your mind.

  • Can the dentin be whitened? YES.

  • Why does teeth whitening cause sensitivity? The bleaching gel can reach your pulp!

The next time you feel teeth sensitivity from whitening your teeth, just remember that it's because your tooth nerve is being bleached. If it sounds painful, that's because it is!

Stain oxidation mechanism

The actual whitening processing is due to oxidation of the tooth stains. Studies have shown that only the organic portion gets oxidized while the inorganic matrix gets left intact.

Basically, the free radicals will convert the double conjugated double bonds of stain molecules to single bonds. The loss of the double bonds will make the tooth stains appear whiter/lighter in color.

Peroxide oxidizes double bonds to single bonds
Peroxide oxidizes double bonds to single bonds

This is a very important concept to understand because the MORE double bonds a stain molecule has, the DARKER that it appears. Consequently that also means the LESS double bonds a stain molecule has, the LIGHTER that it appears.

Degree of conjugation and color of stain
Degree of conjugation and color of stain

Basically, by converting the double bonds to more single bonds, the stain will be getting bleached whiter.

How double bonds affect color

The number of conjugated double bonds have a direct correlation with the pigmentation of molecules. This is because double bonds absorb more light while single bonds reflect more of it.

Please recall what you know about the colors black and white.

  • The color black is when all light wavelengths are absorbed.

  • The color white is when all light wavelengths are reflected.

Therefore, by reducing the number of double bonds which can absorb more light, more of the light will be reflected. This results in the stain molecule appearing lighter in color since more light is now being reflected.

I don't want to blow your mind but... what this technically means is that teeth whitening does not remove stains from your teeth but rather makes them invisible to the naked eye!


We're just going to recap everything that we've learned about teeth whitening and how hydrogen peroxide makes our teeth whiter. It is in most whitening products including whitening toothpastes.

Summary key points:

  • Hydrogen peroxide does not whiten teeth in its current state.

  • The peroxide decomposes into free radicals which are the true whiteners.

  • Free radicals (hydroxyl and perhydroxyl) diffuse through the tooth while oxidizing all of the teeth stains.

  • Stain oxidation involves converting double bonds to single bonds.

  • Less double bonds equate to less light absorption thus a whiter molecule.

  • Teeth stains don't get removed but just become invisible to the naked eye.

I'm willing to bet that I'm the first person that you're hearing this from because most people don't actually understand how hydrogen peroxide whitens teeth. Last but not least, there is a new breakthrough in whitening technology which uses PAP for peroxide-free whitening. In case you wanted to check that out.



David Chen 200 x 200.jpg

About the author: Dr David Chen, DDS

Hello, I'm Dr Chen and I'm an actively practicing dentist in Long Island City, NY. I graduated from Columbia University College of Dental Medicine in 2016 but prior to going to dental school I was already working in the dental field. It's been more than a decade since I first got to know dentistry and let me tell you, time flies by quickly. Since then I've developed a fondness for writing, which is how this all got started!

Association Memberships:

Medical Disclaimer:

This blog is purely meant for information purposes and should not be used as medical advice. Each situation in your mouth is unique and complex. It is not possible to give advice nor diagnose any oral conditions based on text nor virtual consultations. The best thing to do is to go in person to see your dentist for an examination and consultation so that you can receive the best care possible.

The purpose of all of this oral health information is to encourage you to see your dentist and to inform you of what you may expect during your visit. Due to the unfortunate nature of dentistry, there isn't really any true home remedies that will get rid of dental problems. Roughly 99.99% of them require in-person intervention by a healthcare professional.

Hint: That is the reason why you can't eliminate seeing dentists in your life!

bottom of page