Is Teeth Whitening Supposed To Hurt?

Written & Reviewed by Dr David Chen

Teeth whitening has a propensity for causing sensitivity but it depends on the individual and a whole host of factors. Two individuals undergoing the same treatment will walk away with completely different experiences.

zoom whitening light

We will attempt to explain why the teeth become so sensitive and also what can make it worse. Of course we’ll also tell you ways on how to make it not hurt so much!

Why does teeth whitening hurt?

Whitening your teeth can hurt because the peroxide pulls fluids out of the tooth, dissolves smear plugs, and directly reaches the tooth nerve. Each of these three effects may induce teeth sensitivity. They’re also the reasons that make sensitivity one of the two most common adverse effects from whitening.

Peroxide pulls fluids away from the nerve

The hydrodynamic theory of dentinal hypersensitivity states that teeth sensitivity is the result of fluid movements within the dentinal tubules. Various external stimuli will either pull fluids away from or push them towards the tooth nerve. Receptors within the tubules can sense these movements and result in sensitivity signals.

hydrodynamic theory schematic diagram
Credit: Ji won Kim and Joo-Cheol Park

Due to the hypertonicity of hydrogen peroxide, the fluids get pulled away from the tooth nerve. The whitening gel is very acidic and incredibly hypertonic.

This is the most widely accepted theory as to why people feel sensitivity in general. It is not limited to just whitening but all external stimuli.

For instance, cooling, drying, evaporation or hypertonic stimuli will pull fluids away from the nerve. On the other hand, heat and probing will push the fluids towards the nerve. The fluid direction may change depending on the type of stimuli that it is being subjected to.

Various categorization of causes for dentinal fluid movements:

  • Thermal changes such as hot and cold.
  • Physical changes.
  • Osmotic gradients.

Dissolve and dislodge smear plugs

Due to the potency and acidity of the whitening gel, it can dislodge and dissolve smear plugs which normally occlude the dentinal tubules. With the smear plugs gone, there is wide open access directly for stimuli to enter into the tubules. In other words, the tooth will feel the full brunt of the stimuli and fluid movements will react with full sensitivity.

Peroxide gel on smear plugs
Credit: KoR

This is an important concept to understand because under normal circumstances, the smear plugs act as a protective barrier. Since they naturally clog the tubules, they prevent stimuli interacting with the dentinal fluids.

Smear Plugs with and without
Credit: KoR

As a little sneak preview, this is how sensitivity toothpastes like stannous fluoride and nano-hydroxyapatite work. They take advantage of the fact that smear plugs can be used to reduce sensitivity by occluding the tubules. These toothpastes basically recreate their own version of smear plugs to clog up all of the open orifices so that you feel no pain!

Reache all the way to the pulp

Most are under the impression that whitening gel will only whiten the enamel but that is a half-truth. Hydrogen peroxide is actually potent enough to diffuse through every layer of the tooth and even end up at the pulp within 15 minutes.

Studies have shown that the presence of peroxide was detectable at the tooth nerve. That should put to rest your idea that it only affects your enamel. In fact, it will whiten your enamel, dentin, and even the pulp! Of course, most of the effects are happening at the outermost enamel layer. Only a small portion of it will make its way to the pulp.

If you’ve used hydrogen peroxide as a mouthwash before, you’ll know that it stings because it is acidic. Now imagine if acid gets into contact with your nerve, it’ll probably sting as well wouldn’t it?

How painful can get it get?

Teeth sensitivity is a common adverse effect of whitening your teeth but the effects should be mild and transient. Of course that is according to the American Dental Association (ADA).

Your teeth shouldn’t feel like they’re killing you as long as you follow the directions and whiten them properly. It should feel more like sensitivity and not severe pain. However, everyone does react differently and there are factors which affect the severity of the post-op symptoms.


The concentration of hydrogen peroxide in the whitening gel has a direct correlation with how sensitive your teeth can get. The more concentrated the product, the greater the potential for experiencing more severe discomfort. Vice versa, the less concentrated the product the lower the potential for sensitivity and less discomfort.

As an example, you can compare these three products and the amount of sensitivity you may receive afterwards.

  • Whitening toothpaste with peroxide such as Colgate Optic White or Crest 3D brilliance.
  • Whitening strips such as Crest and Moon Oral care.
  • In office whitening such as ZOOM or KoR Whitening.

The lowest concentration product would be the whitening toothpaste. For these you can use them twice a day, day in and day out without experiencing much symptoms at all. The potency was designed to be lower so that you can use it as an everyday product.

The middle ground would be the whitening strips, which are more potent than the toothpaste but less so than a professional product. According to the ADA, discomfort usually doesn’t appear until about the second to third day of using it.

The most concentrated product would be an in-office whitening treatment at your dentist. These have the greatest potential for causing discomfort where you can feel the symptoms almost immediately after treatment. In fact, we’ve had some patients who can’t finish the entire session due to intense sensitivity so they had to stop. We’ve also had individuals who couldn’t sleep the night of getting their teeth whitening.

There is definitely a direct correlation between the concentration of the whitening gel and how much discomfort you may get afterwards.

Duration of treatment

The entire duration of whitening treatment has an effect on the post-operative symptoms. Basically as you continue whitening day after day, the symptoms build and accumulate. The symptoms will not go away as long as you keep whitening.

The sensitivity will only subside after you finish or cease using the product. That means if you’re feeling discomfort during the middle of treatment, it will not go away and can only increase if you continue. You will not “get used to it” if you whiten for a longer period of time.

Pre-existing sensitivity

Unfortunately for some people, they already suffer from pre-existing or chronic teeth sensitivity. For these people, the whitening will only make the symptoms worse. In fact, they may even experience an exaggerated pain response when compared to those who don’t have this pre-existing condition.

Smear plugs and dentinal tubules
Credit: KoR

The reason is because these individuals tend to be chronically missing smear plugs and most likely have enlarged dentinal orifices. Therefore they’re more predisposed to heightened sensitivity towards external stimuli.

For how long do your teeth hurt afterwards?

According to the ADA, pain or sensitivity from whitening treatment should self-resolve four days after finishing. That is how long it takes after you finish or cease using the product. It is not four days after you first start experiencing symptoms.

Needless to say, if you continue using the whitening gels it will continue to be sensitive since the effects are cumulative. What we’re trying to say is that if the discomfort feels as if it is too much for you to handle, you may want to consider pausing the treatment. That is because it won’t be another four days from when you stop using it that you’ll get pain relief.

When do the symptoms start?

Depending on the concentration of the whitening product that you’re using, the symptoms may be felt a few days later or immediately.

  • In-office whitening will typically feel sensitive immediately afterwards or later on during the day. This is due to its very high concentration of peroxide.
  • At home products like whitening strips, you may not feel the symptoms until 2-3 days after starting the treatment. This is due to a lower concentration of hydrogen peroxide within the strips.

How to get pain relief after whitening

The discomfort can be very unsettling but you don’t have to suffer through it. There are ways to minimize the pain and get the relief that you deserve.

How to stop sensitive teeth pain:

  1. Stop whitening your teeth immediately
  2. Receive fluoride varnish treatment at the dentist.
  3. Use a potassium nitrate toothpaste without pyrophosphates AND a nano-hydroxyapatite toothpaste together twice a day.
  4. Take pain medication such as ibuprofen.
  5. Avoid or minimize acidic foods that can aggravate the sensitivity.
  6. If you have whitening trays, wear them to help protect them from the cold air.

Doing all of the above should decrease the discomfort enough that your teeth will have time to recover. After all the symptoms usually self-resolve after 4 days.


It isn’t unusual to feel sensitivity after whitening your teeth because it is a common adverse side effect. The severity of the discomfort will vary depending on the treatment that you received. Typically it’ll be a lot worse if it was an in-office treatment vs an at-home one.

The good news is that all of the discomfort should be transient because it will go away once you cease treatment. The “damage” isn’t permanent because they will all resolve and go back to how they were before. Fortunately for you, at least your teeth will be whiter.

However you should be aware that the whitening doesn’t last forever so you will need to do maintenance or touch ups. If you don’t you’ll need to redo the entire treatment all over again at some point.


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