Whitening comes down to two variables: what active ingredient touches the tooth, and for how long. Almost every price difference in the category is a difference in one of those two things, or in nothing at all.
How whitening actually works
Hydrogen peroxide, or carbamide peroxide which breaks down into it, diffuses through enamel into the dentin underneath and oxidises the pigmented molecules trapped there. That is a chemical change to the tooth's internal colour, not a cleaning. Abrasives, charcoal, and most whitening toothpastes do something different: they scrub surface stain off the outside. Useful, but it stops at the colour your enamel already is.
The options, ranked by what they change
| Method | Active | Typical result | Cost |
|---|---|---|---|
| In-office professional | 25 to 40% hydrogen peroxide | 3 to 8 shades, one or two visits | $300 to $1,000 |
| Dentist-made custom trays | 10 to 22% carbamide peroxide | 3 to 6 shades over 2 to 4 weeks | $200 to $500 |
| Whitening strips | 5 to 14% hydrogen peroxide | 2 to 4 shades over 2 weeks | $25 to $60 |
| Whitening toothpaste | Abrasives, sometimes low peroxide | Surface stain only | $5 to $15 |
| Charcoal, oil pulling, DIY acids | None that whiten | Nothing, and acids erode enamel | Varies |
Custom trays from a dentist are the value pick for most people. The tray is what makes the difference: it holds gel against the tooth and off the gums, which is both more effective and less irritating than a strip that slides. The ADA's consumer overview of teeth whitening covers the same ground, and the ADA Seal list flags the products that have passed independent review.
What whitening will not do
- Crowns, veneers, bonding, and fillings do not change colour. Whiten first, then match new restorations to the new shade. Doing it in the other order means replacing the work.
- Tetracycline staining from childhood antibiotics is deep and banded, and typically needs veneers rather than bleach.
- Grey teeth respond much less than yellow ones. Yellow oxidises well; grey often does not.
- A single dark tooth after trauma usually needs internal bleaching by a dentist, not a tray.
Sensitivity is normal and temporary. Peroxide opens dentinal tubules for a day or two. A potassium nitrate desensitising toothpaste used for a week before and during treatment substantially reduces it. If sensitivity is sharp and localised to one tooth, that is not whitening sensitivity, that is a crack or a cavity. Stop and get it looked at.
Safety, briefly
Peroxide whitening at consumer and professional concentrations has a long safety record when used as directed, and does not soften enamel in any clinically meaningful way at normal contact times. The real risks are gum burns from ill-fitting trays, overuse, and unsupervised high-concentration gels bought online. The ADA's clinical summary on whitening safety and adverse effects reviews the evidence on enamel, pulp sensitivity, and soft-tissue irritation, and is worth reading before you buy an unregulated high-strength gel online.
Making it last
Colour rebounds. Expect to lose some of the result in the first two weeks as teeth rehydrate, then a gradual drift over a year or two depending on coffee, tea, red wine, and smoking. Most people maintain with one or two nights of tray gel every few months rather than repeating a full course. Track it honestly with our whitening shade tracker rather than by memory, because memory is generous.
One note if you are also straightening your teeth: aligner trays double as whitening trays, and several aligner plans, including sponsor NewSmile, include a whitening kit for exactly that reason. Whitening at the end of treatment, once the teeth are in their final positions, gives the most even result.