Hydrogen Peroxide vs Carbamide Peroxide: What's the Difference?

October 7, 2026

Short answer

They are the same whitening agent delivered two ways. Carbamide peroxide breaks down into hydrogen peroxide and urea, and releases about one third of its strength as hydrogen peroxide, so the percentages on the two kinds of gel cannot be compared directly. In studies of tray whitening at home, neither one caused more sensitivity than the other.

How do you compare the percentages?

The American Dental Association states that carbamide peroxide releases about one third of its content as hydrogen peroxide. A European Commission scientific committee puts the figure for a 10% carbamide peroxide gel at a maximum of 3.6% hydrogen peroxide.

Carbamide peroxide on the label	Hydrogen peroxide it releases
10%	3.6% (published figure)
16%	About 5 to 6%
22%	About 7 to 8%
35%	About 12 to 13%

The last three rows are worked out from the one third rule, so treat them as approximate. The practical point is that a 22% carbamide peroxide gel is in the same range as a hydrogen peroxide gel of under 10%, not more than twice as strong.

Which one whitens more?

Neither has a clear lead. A 2016 analysis of eight randomized trials of at-home whitening found carbamide peroxide whitened slightly more when colour was measured by instrument, but not when it was measured against a shade guide, and its authors advise reading that result with caution. A Cochrane review of 71 trials could not say that any one formulation was better than another.

Which one is gentler?

The same 2016 analysis found no significant difference between the two in tooth sensitivity or gum irritation. What does make a difference is strength: the Cochrane review found sensitivity and irritation were more common with higher concentrations, although still mild and temporary.

Why are the wear times so different?

The two are sold for different routines. Hydrogen peroxide gels are worn for short sessions, and carbamide peroxide gels are worn for hours.

Opalescence Go 15% is hydrogen peroxide and is worn 15 to 20 minutes a day.
Philips Zoom DayWhite 9.5% is hydrogen peroxide and is worn 30 to 60 minutes a day.
Philips Zoom NiteWhite is carbamide peroxide and is worn 2 to 4 hours or overnight.

These are the manufacturers' published wear times. Always follow the instructions packed with your gel.

Which one should you pick?

Choose by your routine. If you want a short daily session, pick a hydrogen peroxide product. If you would rather whiten for a few hours at home or while you sleep, pick a carbamide peroxide gel. Gels in syringes need a set of whitening trays. Prefilled trays do not.