The percentage on a teeth whitening gel tells you how fast it works and how likely it is to make your teeth sensitive; it does not tell you how white your teeth will end up. It also only means something once you know which peroxide is in the tube, because 16% carbamide peroxide and 16% hydrogen peroxide are very different products. In Australia the Dental Board draws the line: whitening products over 18% carbamide peroxide or 6% hydrogen peroxide can only be used or supplied by a registered dental practitioner. This guide to teeth whitening gel strengths explains what 6%, 10%, 16% and 35% mean, who may supply each, and how I choose between them.
Written by Dr James Tran, BDent (University of Sydney), MICOI, GradDip (Oral Implants), general dentist at Lumi Dental in Melrose Park.
The short version
- Carbamide peroxide breaks down into hydrogen peroxide and urea, releasing roughly a third of its percentage as hydrogen peroxide, so regulators treat 18% carbamide and 6% hydrogen peroxide as the same line.
- 6% hydrogen peroxide is the strongest level that may be sold directly to consumers in Australia. Anything over that, or over 18% carbamide peroxide, is dental-practitioner only.
- 10% and 16% carbamide peroxide are the usual take-home tray strengths. 35% is practitioner-only, either a short-wear carbamide gel or hydrogen peroxide for in-chair sessions.
- Research has reported that lower take-home strengths reach a similar final shade to stronger ones, with less sensitivity, given enough nights.
- The chemistry behind the two numbers is covered in our guide to carbamide peroxide versus hydrogen peroxide.
The rule: strength sets speed and sensitivity, time sets the end shade
Peroxide whitens by breaking apart the coloured molecules held in enamel and the outer dentine. A stronger gel releases more peroxide each minute, so the shade moves faster, and more peroxide reaches the nerve, so the tooth is more likely to zing. A weaker gel does the same job more slowly with fewer side effects, and it does not set a lower ceiling.
A network meta-analysis of 13 randomised trials of take-home carbamide peroxide found no significant difference between concentrations in shade-guide change, while 10% gel carried a clearly lower risk of tooth sensitivity than 20 to 22% gels. The authors concluded that lower concentrations reduced sensitivity while whitening comparably, though most trials had a high risk of bias. In my experience it holds up chairside: 10% for three weeks and 16% for two usually finish within a shade of each other.
Hydrogen peroxide and carbamide peroxide: two numbers, one active ingredient
Hydrogen peroxide is the molecule that does the whitening. It is unstable, so it works quickly and is finished quickly, which suits short wear. Carbamide peroxide is a more stable compound that reacts with water and breaks down into hydrogen peroxide and urea, and that slow release is why carbamide gels are worn for hours or overnight in a tray.
So the percentages do not line up. The Dental Board pairs 18% carbamide peroxide with 6% hydrogen peroxide as equivalent thresholds, a ratio of about three to one. Carried through, 10% carbamide delivers a little over 3% hydrogen peroxide, 16% carbamide roughly 5 to 6%, and 35% carbamide roughly 12%. So a "35% gel" sold as carbamide peroxide is stronger than any consumer product, but nowhere near the 35% hydrogen peroxide used in the chair.
What each strength is used for
6% hydrogen peroxide
The top of the consumer range in Australia; healthdirect notes that only registered dental professionals can use anything stronger. It is also a common dentist-supplied daytime gel, worn for short periods, typically 30 to 60 minutes once or twice a day over a couple of weeks.
10% carbamide peroxide
The longest track record of any take-home gel. Trials have used it for two to ten hours a day across two to four weeks, most often overnight in a custom tray. With roughly 3% hydrogen peroxide released slowly, it is the gentlest practitioner-supplied option and the one I usually start with for anyone who has ever winced at ice cream.
16% carbamide peroxide
Trials have typically worn 16% for about two hours a night over two to three weeks, which suits people who want a shorter daily commitment. It sits under the 18% consumer threshold, so it appears in some kits, but a loose generic tray lets this much gel pool on the gums.
35%: two different products
As carbamide peroxide, 35% is a practitioner-only gel for short supervised wear rather than overnight. The Dental Board confirms that practitioners can supply higher-concentration take-home products if, after an examination, they judge it safe for that patient. As hydrogen peroxide, 35% is an in-chair product only: the gums are covered with a protective barrier and the gel sits on the enamel for a timed session of 15 to 60 minutes, over one to three visits. Sensitivity on the day is common.
Strength, who may supply it and what to expect
| Gel | Hydrogen peroxide released | Who may supply it in Australia | Typical wear | Sensitivity tendency |
|---|---|---|---|---|
| 6% hydrogen peroxide | 6% | Consumer products up to this level; also dentist-supplied | 30 to 60 minutes, once or twice a day | Moderate; short contact limits it |
| 10% carbamide peroxide | Roughly 3% | Consumer kits and dentists | Several hours or overnight in a custom tray, two to four weeks | Lowest; usual first choice for sensitive teeth |
| 16% carbamide peroxide | Roughly 5 to 6% | Consumer kits and dentists (under the 18% line) | About two hours a day, two to three weeks | Moderate; more gum irritation if the tray is loose |
| 35% carbamide peroxide | Roughly 12% | Registered dental practitioner only | Short supervised wear after an examination | Higher |
| 35% hydrogen peroxide (in-chair) | 35% | Registered dental practitioner only, applied in the chair | 15 to 60 minute session, one to three visits | Highest on the day, usually settles within a day or two |
Stronger gel, same end shade: what the research shows
An umbrella review of 28 systematic reviews found no significant difference in colour change between in-chair and take-home whitening, or between high and low concentration gels, and found sensitivity with every technique. Healthdirect says it plainly: take-home whitening takes longer than in-chair treatment, but that does not mean the final result is better or worse. The chair wins on speed; the tray wins on comfort and control, and many people have both.
Why a kit above the threshold is a red flag
The ACCC has stopped the supply of home-use kits containing more than 6% hydrogen peroxide or more than 18% carbamide peroxide after reports of chemical burns to the gums and mouth, blistering or ulceration of the mouth and throat, tooth sensitivity, and marbled or unnaturally coloured teeth. Its advice: if the concentration is not clearly labelled, do not use the product.
The same logic applies to whitening by people who are not registered dental practitioners. They cannot lawfully use or supply gels above the threshold, so a salon advertising "35% professional strength" is either breaking the rules or misdescribing the gel. Our article on whether salon teeth whitening is safe and legal covers what to ask.
How I choose a strength for a patient
The decision is less about the number and more about the mouth in front of me:
- If you have sensitive teeth, exposed root surfaces or gum recession, start with 10% carbamide peroxide, shorter wear and a longer course. Our guide to whitening sensitivity, its causes and relief explains why.
- If you want the fastest visible change for a date on the calendar, an in-chair session followed by trays is the usual plan, accepting a day or two of sensitivity.
- If the tray is loose or generic, the strength matters less than the leak. A custom tray from a scan keeps gel on the enamel and off the gums; see how custom whitening trays work.
- If you have crowns, veneers or front fillings, no strength will change their colour. Whiten first, let the shade settle, then plan any re-matching.
How we approach this at Lumi Dental
At Lumi Dental in Melrose Park, whitening begins with an examination by a dentist, because gel of any strength on an undiagnosed crack, cavity or inflamed gum causes trouble. The starting shade is recorded, restorations are noted, and a 3D intraoral scan is taken for custom trays. The whitening options are named Home, Refresh and Radiance, and your cosmetic dentist at Lumi Dental recommends one based on stain type, sensitivity history and timeline. The hygiene team of oral health therapists looks after cleans beforehand and whitening maintenance afterwards.
Questions patients ask
Is 35% whitening gel safe to use at home?
Not without a dentist. In Australia, any gel over 18% carbamide peroxide or 6% hydrogen peroxide is practitioner-only, and the ACCC has recalled home kits above that line because of chemical burns and ulceration. A dentist may supply a stronger take-home gel only after an examination.
What percentage of carbamide peroxide is best for whitening teeth?
For most people, 10% in a custom tray, worn for several hours or overnight over two to four weeks. Research has reported it reaches a shade comparable to stronger gels with the lowest risk of sensitivity.
Is 6% hydrogen peroxide strong enough to whiten teeth?
Yes, for yellow surface stain, provided it is worn consistently. It works faster per minute than 10% carbamide peroxide but is worn for less time, so the two often land in a similar place after two weeks.
Does a higher percentage whitening gel work faster?
Faster, yes. Whiter, not usually. Trials comparing concentrations have found similar final shades with more sensitivity at the higher strengths. Our guide to how many shades whiter teeth can go sets realistic targets.
Which strength do the Home, Refresh and Radiance options use?
That is decided at the examination rather than from a menu, because the right strength depends on your enamel, sensitivity history and timeline. Our comparison of Home, Refresh and Radiance whitening explains how the three differ, and a written plan follows the consult.
Not sure which whitening strength suits you? Complimentary cosmetic consult in Melrose Park
If you are weighing up 6%, 10%, 16% or an in-chair session, the team at Lumi Dental in Melrose Park can examine your teeth, record your starting shade and recommend a strength and wear time. Book a complimentary cosmetic consult, or read more about teeth whitening at Lumi Dental. Patients visit from Ryde, Parramatta, Ermington, Rydalmere and nearby suburbs.
Sources
- Dental Board of Australia: Teeth whitening products (fact sheet for registered dental practitioners)
- healthdirect: Teeth whitening
- ACCC Product Safety: ACCC takes action on unsafe teeth-whiteners
- PMC: What is the optimal concentration of carbamide peroxide for at-home bleaching? A systematic review and network meta-analysis
About the author
Dr James Tran is a general dentist at Lumi Dental in Melrose Park. He holds a BDent from the University of Sydney and a Graduate Diploma in Oral Implants, and is a Member of the International Congress of Oral Implantologists (MICOI).
This article is general information only and is not a substitute for an examination and individual advice from a registered dental practitioner. Suitability for any treatment varies from person to person.
