Both hydrogen peroxide (HP) and carbamide peroxide (CP) are bleaching agents that are commonly found in teeth whitening products. Despite the difference in naming, they’re not as different as you may have imagined them to be. For the most part they do whiten your teeth in pretty much the same way.
We’re going to explain everything that you’d want to know about these two whitening agents. That way you can make your whitening purchase with confidence.
Are they the same or are they different?
Carbamide peroxide is a precursor to hydrogen peroxide and is also known as urea-hydrogen peroxide. As its other name implies, CP is basically composed of urea and hydrogen peroxide and is also considered a source for HP.
This is evident in the decomposition of carbamide peroxide where it breaks down into urea and hydrogen peroxide. The HP will then ultimately decompose into water and oxygen. The chemical reactions for both are shown below.
Since CP decomposes into HP, they’re more similar than different since it literally converts into it. In fact, a 10% solution of carbamide peroxide will produce about 3.6% of hydrogen peroxide upon decomposition. Therefore a 1:3 ratio is a good estimate for figuring out how much HP is in CP.
- As an example, a 30% concentration of CP will be equivalent to a 10% concentration of HP.
- That is the formula for figuring out the potency between the two products.
Which one is more effective at whitening your teeth?
In a study by the Journal of the American Dental Association, both CP and HP were equally as effective in whitening teeth. The study compared 7.5% hydrogen peroxide with 20% carbamide peroxide. That is roughly the same concentration of HP when you take into account the 1:3 ratio.
- During the first 14 days, the CP lightened the the teeth more.
- However at the end of the study, both products whitened the teeth to a similar level.
That study was comparing relatively similar concentrations so the end results were not surprising. Since the CP converts into HP and the concentrations were relatively similar so the results should be as well.
It makes sense if you understand the mechanism for how teeth whitening works. What actually whitens teeth is the free radicals which are produced when hydrogen peroxide decomposes. There are multiple intermediate steps during the decomposition which produces a lot of free radicals, which are powerful oxidizers. They’re potent enough to oxidize intrinsic tooth stains by diffusing through the tooth.
The chemical reactions above show all of the decomposition steps of hydrogen peroxide. For carbamide peroxide, it is nearly identical except for the fact that it has an extra step as a precursor. The CP first needs to decompose into HP before it goes through the steps above. Nonetheless, the whitening agent, perhydroxyl (HO2) remains the same for both CP and HP.
Essentially having relatively similar concentrations will yield an equivalent amount of perhydroxyl, thus the efficacy should be similar. To learn more about the whitening mechanism, please check out our article on how hydrogen peroxide whitens teeth.
Which one whitens teeth faster?
When the concentrations are relatively similar, the hydrogen peroxide will whiten teeth faster. It will decompose into perhydroxyl quicker because it is less stable and it requires less steps to get there.
Studies have shown that carbamide peroxide is more stable than HP and does not break down as readily. Due to that feature, it is actually more desirable to formulate OTC whitening products with CP since that makes it more shelf stable.
Hydrogen peroxide on the other hand is very sensitive to light and heat which makes it decompose naturally. That is why you always find it in brown bottles at the pharmacy! Consequently it produces the perhydroxyl radical for whitening more readily.
Another reason that HP whitens faster is that it requires less steps than CP to produce the whitening free radicals. CP has an extra step in that it needs to first decompose into HP before it can start creating the radicals.
That extra step for converting carbamide peroxide to hydrogen peroxide creates a delay before it can start whitening. According to Opalescence, hydrogen peroxide exerts most of its whitening effect within 30-60 minutes. That is in contrast to carbamide peroxide which exerts 50% of its whitening effect in the first 2 hours and slowly releases the rest over the next 6 hours.
You can think of the carbamide peroxide as an extended release formulation of hydrogen peroxide. Don’t forget that they will both whiten teeth to the same level, it’s just that it takes CP a little longer to get there. All of this can be observed from the recommended whitening time of various concentrations of Opalescence products.
| Product | Amount of HP or CP | Recommended Daily Wear Time |
| Opalescence Go, 6% | 6% Hydrogen Peroxide | 60-90 minutes/day |
| Opalescence PF Gels, 10% | 10% Carbamide Peroxide | 8–10 hours or overnight |
| Opalescence PF Gels, 16% | 16% Carbamide Peroxide | 4–6 hours |
From the chart above you can see that hydrogen peroxide based products require less treatment time. CP products typically require a longer treatment time but you can also see that as you increase the CP concentration the wear time decreases.
Effect of concentration on whitening speed
Studies have shown that higher concentrations of whitening gels will whiten teeth faster. That is consistent by how in the chart above, an increase in concentration produced a decrease in required whitening time.
However you should also be aware that while concentration may affect whitening speed, the end result will be the same when given enough time. That means low concentration whitening products can whiten teeth to the same level as higher concentration ones. It simply just takes more time for it to get there.
Studies have actually proven that the concentration of your whitening product is irrelevant. All can potentially whiten your teeth to the same level. When you pay for a more concentrated product, you’re simply paying to get the result faster. The ultimate whiteness will remain the same as long as you use the products as directed.
As evidence, this study compared the whitening efficacy of a 10% carbamide peroxide product with a 16% one. There were no significant differences in color change between the two concentrations at the end of the experiment.
Is hydrogen peroxide better than carbamide peroxide?
Since the HP will whiten your teeth faster, it doesn’t actually mean that it is better than CP. The reason is that they can be used for different purposes.
One particular use for low concentration carbamide peroxide is in its ability to whiten your teeth overnight. Since it acts more of like an extended release formula, it makes it perfect for doing it while you sleep for the next 6-8 hours.
On the other hand, HP cannot do that because it’ll be finished working well before you’re done sleeping. It is also more potent so that makes it more suited for daytime whitening or in-office sessions.
Does one cause more sensitivity than the other?
The amount of sensitivity for both carbamide peroxide and hydrogen peroxide should be the same if the relative concentrations are the same. The reasoning is that the whitening agent is the same for both, the free radical perhydroxyl which diffuses through the tooth while oxidizing stains.
Therefore there shouldn’t be any differences in sensitivity since the amount of oxidizing radicals are the same.
However what would increase teeth sensitivity if you used a higher concentration product. That is regardless of whether it is HP or CP. A more potent product for both would result in more sensitivity. This is why in-office whitening is usually more sensitive than the whitening strips that you use at home.
Will one of them rebound in color more?
Since both products whiten teeth via the same exact mechanism, there is no reason for them to rebound differently. All of the teeth will rebound in color at the same rate. It all depends on how much staining foods and drinks that you eat.
The more red wine, coffee, and tea that you consume the faster your teeth will return back to yellow. The good news is that if you can minimize or avoid the consumption of pigmented foods you can extend the whiteness of your teeth. Of course you can also slow down the staining if you do periodic whitening maintenance.
Which one is more shelf stable?
Carbamide peroxide is more shelf stable than hydrogen peroxide and will decompose at a slower rate. The CP is more stable because it comes in solid state since it has urea mixed in it.
Since it is more stable, it makes for a better OTC commercial product since it lasts longer on the shelves. With hydrogen peroxide, you need to store it in a container that keeps it away from light.
However studies have shown that refridgeration can help extend the shelf life of both CP and HP. While CP is more resistant and stable, they’ll both degrade in the presence of heat. By storing it in cold temperatures, the product will be more fresh when you use it.
The Verdict
In terms of whitening, carbamide peroxide and hydrogen peroxide have essentially the same efficacy since the active whitening agent is identical. All peroxide based products utilize the free radical perhydroxyl (HO2) to chemically bleach your teeth.
- Hydrogen peroxide decomposes into perhydroxyl.
- Carbamide peroxide decomposes into HP, which then breaks down further into HO2.
- The ratio of CP:HP is 3:1 or in other words you divide the concentration of CP by 3 to get the HP concentration.
The only real difference is that CP was created to be more shelf stable since HP is very unstable. That helps in preserving its efficacy while in storage waiting to be sold. Therefore there is a higher chance that your CP product is more potent than HP due to it being more resistant to decomposition. Professional whitening products will use both CP and HP so you shouldn’t be worried that one is better than the other.
Nevertheless the end result for how white your teeth can get will pretty much end up being very similar when used over a long period of time. Both of them will remove both types of teeth stains, extrinsic and intrinsic ones. That is what studies have shown so you really can’t go wrong with choosing either product.