Carbamide peroxide is a compound made from equal parts hydrogen peroxide and urea that releases hydrogen peroxide slowly when it contacts water or saliva. You’ll find it in teeth whitening gels, earwax removal drops, and oral wound treatments. It’s essentially a more stable, slower-acting delivery system for hydrogen peroxide, which is the ingredient doing most of the actual work.
How Carbamide Peroxide Works
The compound is a 1:1 combination of hydrogen peroxide and urea pressed into a solid. When it dissolves in water or saliva, it breaks apart and releases hydrogen peroxide as the active agent, along with urea (a harmless byproduct your body already produces naturally). Because of the urea component, carbamide peroxide contains roughly one-third the concentration of active hydrogen peroxide. A 30% carbamide peroxide gel, for example, delivers about 10% hydrogen peroxide.
This slower release is the key advantage. Pure hydrogen peroxide starts working immediately and breaks down quickly, while carbamide peroxide releases its payload gradually over hours. That makes it well suited for products designed to sit against your teeth or in your ear canal for extended periods.
Teeth Whitening
Teeth whitening is by far the most common use. Carbamide peroxide gels typically come in concentrations between 10% and 22% for at-home use. The hydrogen peroxide released from the gel penetrates tooth enamel and reaches the colored organic compounds (called chromogens) trapped inside. It breaks down the chemical bonds that give those compounds their color, effectively bleaching the stain from within the tooth rather than scrubbing it off the surface.
At-home whitening trays are usually worn overnight or for several hours at a time. The slow release of carbamide peroxide is what makes these extended wear times practical. A product using pure hydrogen peroxide at the same effective concentration would deliver its full dose much faster, which can increase irritation without improving results for take-home use.
In terms of side effects, tooth sensitivity and gum irritation are the two most discussed concerns. Clinical data paints a relatively reassuring picture. In one controlled study comparing 10% and 16% carbamide peroxide to a placebo, researchers found no statistically significant differences in tooth sensitivity, changes to gum tissue, or effects on tooth vitality. The 16% concentration did cause more gum irritation than the 10%, though. Interestingly, 20% of participants in that study reported sensitivity just from wearing the tray with no whitening agent at all, and 36% reported sensitivity to the placebo solution, suggesting that physical contact with the tray itself accounts for a meaningful share of the discomfort people attribute to whitening.
Earwax Removal
Over-the-counter earwax drops commonly use carbamide peroxide at 6.5%, dissolved in glycerin. When the drops contact earwax, the compound breaks down and releases oxygen bubbles. You can hear and feel this as a gentle fizzing. The bubbling action, combined with the softening effect of the glycerin base, loosens and breaks apart hardened wax.
Lab testing shows the effect is relatively fast. Earwax exposed to carbamide peroxide shows visible breakdown within minutes, with significant degradation after 20 minutes and near-complete breakdown after 40 minutes at body temperature. In practice, most product instructions call for leaving drops in the ear for several minutes, then tilting the head to drain.
Mouth Sores and Oral Wounds
Carbamide peroxide also works as an oral debriding agent for canker sores and minor mouth irritations. In this role, it kills bacteria around the wound, loosens debris and plaque, and supports tissue healing. The typical method is placing several drops directly on the sore and spitting out after two to three minutes, or placing about 10 drops on the tongue, swishing with saliva, and spitting out. These products are meant for short-term use to manage discomfort while the sore heals on its own.
Why It’s Used Instead of Pure Hydrogen Peroxide
Carbamide peroxide exists as a product ingredient largely because of stability. Pure hydrogen peroxide is reactive and breaks down when exposed to light, heat, or contaminants. Carbamide peroxide is a solid at room temperature and holds up significantly better in storage. Research on gel formulations found that carbamide peroxide gels stored under refrigeration maintained their potency for roughly 100 days, while the same gels stored at high temperatures (around 104°F) lost effective concentration in just 24 days. The raw powder itself is even more stable, holding up well at both refrigerated and elevated temperatures as long as the container remains sealed.
This is why whitening gels often come with instructions to refrigerate them, and why dentists may store professional whitening products in a refrigerator. A gel that has been sitting in a hot warehouse or car for weeks may have lost a significant portion of its active ingredient before you ever open it. If your whitening product has been exposed to heat for an extended period, it may simply be less effective rather than harmful.
Concentration and What the Numbers Mean
The percentage on the label refers to the carbamide peroxide concentration, not the hydrogen peroxide you’re actually getting. Since carbamide peroxide yields about one-third hydrogen peroxide by weight, here’s what the common concentrations translate to:
- 10% carbamide peroxide delivers roughly 3.3% hydrogen peroxide. This is the most studied at-home whitening concentration and a common starting point.
- 16% carbamide peroxide delivers roughly 5.3% hydrogen peroxide. A moderate step up with slightly more gum irritation potential.
- 22% carbamide peroxide delivers roughly 7.3% hydrogen peroxide. Typically the highest concentration in consumer take-home kits.
- 6.5% carbamide peroxide is the standard for earwax removal drops, where the goal is gentle fizzing action rather than bleaching.
Higher concentrations whiten faster but don’t necessarily produce better final results. Many dentists recommend starting with 10% and increasing only if needed, since the lower concentration achieves similar outcomes over a slightly longer treatment period with less risk of irritation.