How DOES Teeth Whitening Work? Products And Their Mechanisms

Written & Reviewed by Dr David Chen

Teeth can discolor and become yellow due to two different types of stains, extrinsic and intrinsic stains. For your teeth to become white again, you must reverse the process and remove each type of stain with the proper treatment.

spilled glass of red wine
Wine Stain

Extrinsic stains can be removed mechanically or chemically while intrinsic stains can only be removed with the latter. Therefore choosing the correct whitening product for the type of tooth stain that you have is of utmost importance.

  • Whitening products that only remove extrinsic stains all work in the same way by using abrasives to abrade away the stains.
  • Products that remove both extrinsic and intrinsic stains all work the same way by using peroxide to oxidize the stains.

If you understand which of the two categories your product falls under, you will understand the mechanism for how it will whiten your teeth. The main differences among all of the various types of whitening products are based on three factors.

  • The concentration of peroxide.
  • Treatment duration.
  • Delivery method of the whitening gel.

Now without further ado, let’s dive right into everything that you’d ever want to know about how whitening works and how each product does it.

Mechanism for removing each type of stain

Teeth can be stained extrinsically or intrinsically, with the location of the stain being the main difference between them.

  • Extrinsic stains are located on the exterior of the tooth.
  • Intrinsic stains are located on the interior of the tooth or embedded within the enamel.

Likewise it is also due to their location which determines how each stain can be removed. Stains on the exterior of the tooth can be mechanically removed while the interior ones are shielded from mechanical means. That leaves chemical removal as the only option for intrinsic stains.

However it is important to understand that untreated extrinsic stains can slowly work their way into the tooth and become intrinsic. If having whiter teeth is a goal, do not procrastinate on your cosmetic journey because it only makes it more difficult the longer you wait.

Intrinsic stains require chemical oxidation

Intrinsic stains are immune to mechanical removal and thus require chemical oxidation.

Mechanical removal does not work for intrinsic stains because they can’t physically reach them. These stains are all located beneath the surface of the enamel which protects them from physical harm. Therefore brushing with whitening toothpaste and getting a professional dental cleaning, won’t make a dent in these stains at all. To put it simply, you can’t brush or clean the inside of your tooth!

Chemical agents such as hydrogen peroxide can remove intrinsic stains because it can diffuse through the enamel and oxidize them. Being able to penetrate through the tooth allows peroxide to reach these stains that mechanical means cannot.

How oxidation whitens your teeth

Hydrogen peroxide (HP) is an oxidizing agent but what whitens your teeth is perhydroxyl, a free radical that is produced during the decomposition of HP. The perhydroxyl will oxidize the double conjugated bonds of stain molecules, thus making them appear invisible to our eyes.

Hydrogen peroxide will fully decompose into water, oxygen, and heat.

hydrogen peroxide decomposition one step

However there are intermediary reactions which take place that produce many free radicals. The most notable is perhydroxyl (HO2) which is a very powerful oxidizer that cannot only oxidize intrinsic but also extrinsic stains as well.

hydrogen peroxide decomposition to radicals - reaction equations

The oxidation process will convert the double bonds in stain molecules to single bonds. That makes the stains appear white to our eyes. Technically, the stains don’t get removed because they are still there. They just look whiter so a more accurate description would be that the stains have become invisible to our sight.

Hydrogen peroxide oxidation of double bonds
Credit: Clifton Carey
Oxidation of double bonds makes stains whiter

The amount of conjugated double bonds in stain molecules are directly proportional to how dark they appear to our eyes.

  • The more double bonds it has, the more light it absorbs and the less of it it will reflect.
  • The less double bonds it has, the less light it absorbs and the more of it it will reflect.

Therefore the entire bleaching process can simply be described as a conversion of double bonds to single bonds. It doesn’t actually remove the stains because it just makes them appear invisible instead.

Extrinsic stains can be oxidized or mechanically removed

In contrast to intrinsic stains, extrinsic ones have more options for removal. They can be oxidized with peroxide based products just like the intrinsic ones or they can be mechanically removed. Although it would be preferable to remove the extrinsic teeth staining by mechanical means since it is simpler and has less side effects.

Since this type of stain is located on the external surface of your tooth, brushing and getting a dental cleaning will be effective. The toothbrush and your dentist’s scalers can reach these stains.

What we mean by mechanical removal is by physically getting rid of the stains. In the case of brushing, it is the scrubbing action with abrasives in whitening toothpaste that gets the stain off. Yes, the vast majority of whitening toothpastes’ whitening efficacy is solely reliant upon the abrasive in it.

colgate optic white pro series - on floor

That’s just how whitening toothpastes work, at least the ones without peroxide. The ones that do will possess oxidation potential and is actually a criteria for being the best whitening toothpaste.

In the case of a professional teeth cleaning, your dentist will scrape the stains off with their scalers. We just want to emphasize that it is a very physical process which is contrary to bleaching with hydrogen peroxide. The scraping requires a lot of manual muscle power while the bleaching you just leave the gel on the teeth and let it work its magic.

Nonetheless, in our opinion if you do have extrinsic stains we recommend removing them mechanically rather than chemically. The reason is that chemical oxidation doesn’t physically remove the stains but just makes them invisible. The stain molecules remain in your teeth.

Therefore if you have the extrinsic ones, you should use mechanical means to actually remove them and not just make them whiter. The process also produces less teeth sensitivity as well since bleaching is associated with increased sensitivity. The symptoms may be mild and transient but it is still discomforting.

How each teeth whitening product works

With the exception of whitening toothpaste which can mechanically abrade away extrinsic stains, most whitening products work via oxidation. Therefore the mechanism via how they work and whiten your teeth are all the same.

The differences among them are simply due to their:

  • Concentration of peroxide in it.
  • How long you’re supposed to whiten with them.
  • How they apply or deliver the peroxide to your teeth.

Peroxide is peroxide so from a chemistry standpoint, the way they work are identical. The most common one you see is hydrogen peroxide but some of the products use carbamide peroxide, which is a precursor to HP. It is essentially urea-hydrogen peroxide which decomposes into hydrogen peroxide in a 3:1 ratio. For example, 30% carbamide peroxide is equivalent to 10% hydrogen peroxide.

Additional reading: Carbamide peroxide vs Hydrogen peroxide.

Now without further ado, we gill go through the nitty gritty on how each type of whitening product known to man works and how to use them.

Whitening toothpaste

There are two types of whitening toothpastes, the ones that whiten solely based on abrasives and ones that use abrasives with peroxide. The former can only remove extrinsic stains while the latter can remove extrinsic and oxidize intrinsic ones. Obviously the advantage goes to the latter. That is why we believe the colgate optic white pro series with its 5% hydrogen peroxide formulation is the best whitening toothpaste.

How to use it:

  1. Wet your mouth with a quick rinse.
  2. Wet your toothbrush.
  3. Apply whitening toothpaste to your brush.
  4. Brush for at least 2 minutes twice a day.
Crest 3D white professional

The toothpastes with only abrasives in it will whiten by mechanically scrubbing your teeth with a toothbrush. If it contains peroxide then it will also exert an oxidation effect.

This is one of the easiest and least expensive ways of making your teeth whiter. Everyone has to brush their teeth regardless of if they want a hollywood white smile or not!

Whitening mouthwash

This mouthwash is hydrogen peroxide based and it works by swishing it around your mouth for a specified amount of time. Your teeth will become whiter due to the peroxide coming into contact with it.

How to use it:

  1. Pour specified amount into cap.
  2. Swish and rinse for specified duration of time.
  3. Spit back out.
optic white advanced whitening mouthwash

Examples of whitening mouthwashes:

  • Colgate optic white mouthwash
  • Crest pro health extra whitening mouthwash
  • Plain hydrogen peroxide

Using a whitening mouthwash is also fairly inexpensive when compared to all of the other products available such as strips or even trays. Although the best part about it is that you can still use all of those products in addition to using this mouthwash.

Whitening pen

The whitening pen is very similar to a tide pen which is meant for clothing except in this case it is used for your teeth. It works by coming with an attached brush that allows you to paint the peroxide directly onto your teeth. Then you whiten overnight by going to sleep with it painted on. It usually forms a film over your chompers.

How to use it:

  1. Brush and floss your teeth.
  2. Click the pen to dispense whitening gel.
  3. Paint the gel onto the cheek/lip facing surfaces of all your teeth.
  4. Go to sleep.
  5. Wake up and brush off the residue.
colgate whitening Pen

Examples of whitening pens:

  • Colgate optic white pen
  • Smiledirect club whitening pen
  • Philips zoom whitening pen
  • Aura glow pen

The pen is still fairly inexpensive and should work better than the toothpaste and mouthwash since it is more concentrated.

Whitening strips

The strips are one of the most popular whitening options. Essentially what separates it from the rest is that it delivers the gel in a flexible adhesive strip. It works by sticking one strip to the top teeth and one to the bottom, then you wait for it to work its magic.

How to use:

  1. Remove strips from packaging.
  2. Apply to upper and lower teeth.
  3. Wait stated duration of time.
  4. Remove strips and you’re done!
crest white strips - different view

Examples of whitening strips:

  • Crest 3D whitestrips
  • Lumineux
  • Solimo
  • Zimba
  • Moon dissolving strips

The whitening strips are still considered relatively inexpensive and affordable. Their advantage is that the flexible strips act as a barrier which protects the gel from salivary peroxidase trying to degrade them.

OTC Whitening trays (with and without LED light)

These are prefabricated trays that are available over the counter and some of them even come with a blue LED light. This product works by using the tray as a delivery method for the peroxide gel. Some of the trays are pre-filled while others you have to apply the gel either on your teeth or into the tray.

iwhite non peroxide teeth whitening

Due to the variation in this product you will need to follow their directions closely. The purpose of the whitening light is to accelerate the bleaching gel by making it work faster and better. The LED light is supposed to activate the gel by inducing decomposition so that it produces free radicals for oxidation.

Examples of OTC whitening trays:

  • SNOW whitening
  • iWhite
  • Opalescence GO
  • Auraglow prefilled trays

This is probably the more expensive OTC option but it is still less expensive than all professional options. Their advantage lies in the fact that it comes with a LED light activator and the trays serve as a saliva barrier.

Customized whitening trays

This is the least expensive professional whitening option but it requires a trip to the dentist. Your dentist needs to take molds of your teeth and fabricate a customized tray that fits only for your mouth. Then you simply place the peroxide directly into the tray and then you wear the trays for a specified amount of time.

How to use it:

  1. Brush and floss your teeth thoroughly.
  2. Squirt the peroxide into the facial surfaces (cheek/lip facing) of the tray.
  3. Wear the trays for specified duration of time.
  4. Remove trays and rinse out.
opalesence whitening gel in a tube


  • KoR Whitening
  • Opalesence PF

The customized trays are one of the most effective whitening options that you can do at home. The trays are customized to the shape of your teeth so you get a very even whitening effect. They also serve as protection against saliva. The perk is that you can keep the trays and reuse them. You just need to purchase refills of the whitening gel so it actually works out to being not as expensive as you may think.

In-office whitening (with and without LED light)

This is the only type of whitening treatment that is performed in-office at the dentist. Some of them utilize a blue LED light while others do not. Regardless of whether a LED light is present or not, the peroxide gets applied directly onto the teeth. The gums, cheeks, and lips are typically isolated with cotton rolls. There is also a saliva ejector that suctions it all up.

Kor whitening placing whitening gel

How it is done:

  1. Isolate the teeth by applying a gum barrier along with cotton rolls.
  2. Apply whitening gel directly onto teeth.
  3. Place LED light if there is one.
  4. Let the gel whitening for specified duration of time.
  5. Repeat for however many sessions were prescribed.
  6. Remove the gum barrier and all isolation.
opalesence boost in-office

Examples of in-office whitening products:

  • KoR Whitening
  • ZOOM
  • Opalesence BOOST

The advantage of the in-office treatment is that it comes in the highest concentration of peroxide possible. It will whiten your teeth in the fastest way possible, usually in about an hour session. That is significantly faster than using the strips which you have to do for a week or two.

The downside to this treatment is that it usually comes with more severe teeth sensitivity afterwards. That is all due to the fact that the concentration of peroxide is much higher than OTC products, 30%+ vs 5-15%.

How non-traditional whitening products work

According to the American Dental Association (ADA), do it yourself whitening does not work and is usually harmful for your teeth. If you were to try them, you’d be doing it at your own risk because no major dental organization endorses any of them.


Non-peroxide teeth whitening is quite interesting so to speak because according to our research, they’re not really peroxide free.

  • Phthalimidoperoxycaproic acid (PAP). PAP is actually a synthetic peroxy acid that is made by adding sulfuric acid to hydrogen peroxide. It literally uses peroxide to be made…
  • Sodium percarbonate. According to PubChem, a synonym for sodium percarbonate is actually “sodium carbonate peroxide”. All these marketing tactics are using an alternative name to make you believe that it is not a peroxide…

They’re certainly marketed as not having any peroxide in them since their names don’t have peroxide in them. However if you do even a little bit of research you’d realize that these products either contain peroxide or were derived from them.

The question that we would like to ask you is, are they truly peroxide free? To us the answer is a resounding NO so don’t get fooled. Nevertheless these “peroxide free” products will whiten your teeth just like how hydrogen peroxide would!


There are a plethora of DIY teeth whitening with fruits and one of the most popular one is with strawberries. It is usually concocted with a mixture of baking soda and fresh strawberries. Then you just brush it on your teeth and let it marinade.

Unfortunately according to studies, this form of whitening is one of the least effective whitening modalities. We could even argue that it is dangerous to do it because strawberries are acidic. You’re essentially brushing acid onto your teeth which can erode away your enamel.

Sure if the layer of enamel was stained and you eroded it away with acid, your teeth may appear brighter. However your enamel is now thinner and the worst part is that it doesn’t grow back!


Another popular DIY whitening method is with coconut oil pulling or any other form of oil as well. Allegedly by swishing oil around in your mouth for 15-20 minutes you can pull the stains off of your teeth.

coconut oil

Unfortunately studies have demonstrated that coconut oil pulling has zero effect on whitening your teeth. There are only two proven ways to whiten teeth, via abrasives or oxidation and oil pulling has neither.

Baking soda

Sodium bicarbonate (baking soda) is actually an effective way to whiten your teeth but it can only remove extrinsic stains. That is because it is a legitimate mild abrasive and is in a lot of toothpastes particularly the all natural ones which use it as a base. Studies have shown that it is quite effective and safe for your teeth.

Baking Soda

There are multiple ways to whiten your teeth with baking soda so you should check out our guide for further details. The mechanism via how they do it is by utilizing its abrasiveness.

The only downside to using this product is that it lacks the ability to oxidize intrinsic stains. Therefore if your teeth stains are embedded inside of the tooth, you’ll be out of luck. In that case you should look for a peroxide based product.

Activated charcoal

Toothpastes with activated charcoal can whiten your teeth but it works via the same manner as baking soda. It is an abrasive which can mechanically removal extrinsic stains.

However there are concerns about the safety of using activated charcoal on your teeth because it can be too abrasive for the enamel. Studies have shown that those who brushed with charcoal typically ended up with a lot of tooth abrasions. These surfaces are all missing pieces of the enamel because they were abraded away by charcoal.

Therefore the ADA cautions the use of charcoal based products on the grounds of insufficient studies on safety and efficacy of it. With that being said, we did however find a couple of charcoal toothpastes which allege that it is within the safety limits of abrasiveness.

Factors which influence efficacy of whitening

Not all whitening products are equally as effective because there factors which influence how well they work.

  • Concentration. Studies have actually shown that even low concentrations of peroxide can whiten teeth to the same level as higher concentrations. However the more concentrated products will whiten your teeth faster and that is why we think it works better.
  • The pH of the product. Studies have shown that as you steadily increase the pH of the gel, it becomes more potent with whitening up to a pH of 9. The downside is that storing it in an alkaline environment will cause it to degrade faster which is worse for its shelf-life.
  • Saliva protection. Our saliva naturally contains salivary peroxidases which inactivate peroxide as a self defense mechanism. Products which can protect the gel from saliva will be more effective than those without. For instance, the act as a barrier against saliva and thus work better than say whitening toothpaste.
  • Shelf stability. Hydrogen peroxide will naturally decompose all on its own because it is unstable. That is why it comes in a brown bottle to protect it from sunlight in order to extend the shelf life. However carbamide peroxide which is a precursor to hydrogen peroxide happens to be more stable. It breaks down slower so it may be “fresher” if you purchase OTC products with it instead of hydrogen peroxide.

How long does it take for my teeth to whiten?

The amount of time it takes for your teeth to lighten in color is highly dependent upon the concentration of peroxide in the product. The more concentrated it is, the faster you will see results. This is why in-office whitening which has the most potent whitening gel will give you instantaneous results as opposed to whitening at home with the strips.

According to a study by Dental Materials, which compared 0%, 10%, and 17% carbamide peroxide.

  • Whiter teeth was observed after 3 days of using the 17% gel.
  • For the 10% it took about a week for a noticeable color change.
  • However at the 1 week mark, there were no significant differences in whitening between the 10% and 17% groups.

That is simply to give you a rough idea of what to expect. Of course if you get an in-office session you will see results after an hour! It definitely costs more but that is similar to how same day delivery also costs more. You pay more to see whiter teeth faster.

Am I a candidate for whitening?

Nearly everyone is a candidate for whitening their teeth except if you have these conditions:

  • Chronic teeth sensitivity. If your teeth are already sensitive, whitening them will only make them more sensitive. However that doesn’t mean that you can’t do it… but you may need to stick with the low concentration products which are more gentle and tolerable.
  • Active cavities. If you have untreated cavities, the whitening gel may cause you excruciating pain. The reason being a cavity is a hole in your tooth and that means the peroxide will flow straight to your tooth nerve which is not pleasant. Although technically you can still whiten with cavities but it is not recommended.
  • Pregnant. The ACOG recommends against elective procedures while you’re pregnant and teeth whitening is one of them.
  • Full dentures. If you don’t have any teeth you can’t whiten them. To change the color of your dentures you’d need to get a brand new set.

As long as you don’t have any of the above conditions, you should be clear to proceed with teeth whitening. We do recommend getting a dental check up and a professional teeth cleaning before you start because you want a clean surface to whiten. If your teeth were covered with tartar build up, the whitening gel would have a difficult time reaching your teeth.

Side effects

According to the ADA, the most prominent adverse effects with whitening your teeth are sensitivity and gum inflammation. The good news is that the symptoms are usually mild and transient with self recovery after approximately 4 days of stopping treatment.

However if you continue to whiten your teeth, you will continue to experience symptoms. The resolution only begins after you cease using the product. Nonetheless, just because it takes four days for it go away, it doesn’t mean you just sit around and wait. There are ways to decrease teeth sensitivity from whitening.


There are basically two types of teeth stains, extrinsic and intrinsic. The former can be removed mechanically with abrasives or chemical oxidation. The latter can only be oxidized chemically with peroxide.

All whitening products will use either of the two mechanisms to make your teeth whiter. They just differ based on their concentration and their method of applying the whitening gel to your teeth.

Feel free to give any or all of them a try to see which one works best for you. Although if you asked us to rank them in terms of efficacy we would list them as such.

  1. In-office treatments.
  2. Customized trays by your dentist.
  3. Pre-fabricated trays with or without LED light.
  4. Whitening strips or pen.
  5. Whitening toothpaste.
  6. Whitening mouthwash.

However you should be aware that typically the more efficacious it is the more it would cost so there is a trade off there. You will have to spend more if you want to see results faster.

But at the end of the day, despite how much we adore whitening we just want to remind you that yellow teeth are still healthy. They may not look cosmetically pleasing but they function the same way as white teeth. You’ll still be able to chew and talk without any issues despite them being yellow.

If you want your yellow teeth to become white again, it is certainly a goal to work towards. However if you don’t make it there, you shouldn’t stress out about it too much since they’re still healthy!


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