Do Whitening Strips Work? What the Evidence Can and Can't Say

Yes, peroxide whitening strips work in the sense that matters most: in controlled trials they lighten teeth more than a placebo strip does. What the research cannot tell you is how much lighter your own teeth will get, how long it will last, or whether one brand beats another.

That gap between "works" and "works for you" is where most disappointment with strips comes from. This guide sets out what the evidence shows, which strips it covers, and the situations in which a strip will not do what the box implies.

What the research actually found

The largest independent summary is a Cochrane review published in 2018, and its answer is a qualified yes. It pooled 71 randomised trials of home-based whitening and found that the bleaching agents tested, including hydrogen peroxide strips, whitened teeth compared with a placebo over periods from two weeks to six months.

The qualification is the part adverts leave out. The reviewers rated the certainty of that evidence as low to very low, because many comparisons rested on single small trials, 67 of the 71 trials had an unclear risk of bias, and methods varied from study to study. They also said the evidence was insufficient to say whether any particular product, concentration, application method or length of use was better than another.

So "clinically proven" on a box usually means the seller ran or paid for a study of its own product. That can be a real result, but it is not the same as independent evidence that it beats the strip next to it on the shelf.

Which strips the evidence covers

The evidence covers peroxide strips, which bleach the colour inside the tooth. It does not cover every product sold as a "whitening strip", and that distinction matters more than the brand.

The ADA says most whitening strips rely primarily on peroxide to bleach teeth, either hydrogen peroxide or carbamide peroxide, which releases about one-third of its content as hydrogen peroxide. Those are the strips the trials tested. Other products look the same but work differently:

• PAP strips use phthalimidoperoxycaproic acid, an oxidiser sold as a peroxide alternative. PAP was not among the agents covered by the 2018 Cochrane review.
• Purple strips tint the surface so yellow looks less yellow. Their sellers describe the effect as temporary and optical, and we explain it in our guide to purple whitening strips.
• Strips without a named bleaching agent may only lift surface stains. If the product page talks about stains and polish but does not name a peroxide, assume that is what it does.

The ADA Seal of Acceptance is one way to find a strip that has been checked. Crest 3D Whitestrips is listed in the ADA's Seal product search under tooth whitening, with the accepted claim "Helps whiten teeth".

What strips can change and what they can't

Strips can lighten the natural colour of healthy enamel and dentin; they cannot change anything that is not natural tooth. The ADA says "only natural teeth can be whitened, not tooth-colored restorations", and Crest's own label says its strips will not whiten caps, crowns, veneers, fillings or dentures.

That has a practical consequence. If a front tooth has a crown or a large tooth-coloured filling, whitening the teeth around it can leave that tooth looking darker than before. A dentist can tell you in one visit whether that applies to you.

The type of stain matters too. The ADA separates extrinsic stains, which sit on the surface from coffee, tea, red wine or tobacco, from intrinsic stains, which sit inside the tooth from ageing, some medicines taken in childhood, or a tooth whose nerve has died. Surface stains often respond to a whitening toothpaste or a professional clean. Peroxide reaches deeper, but some intrinsic stains respond slowly: the ADA notes that tetracycline staining can take three to four months of nightly treatment on average, which is far beyond a box of strips.

How long strips take compared with other routes

Strips are the slow route. A study summarised by the ADA found an over-the-counter bleaching technique took 16 days to reach the whitening that a seven-day at-home tray system and a one-day in-office treatment achieved.

That fits what the labels say. Crest's Professional White directions are one treatment a day for 45 minutes for 20 days, and BURST describes a 7-day course of 15-minute treatments. Shorter wear times or fewer days per box do not mean a weaker product, and longer ones do not mean a stronger one; the only way to compare is the strength and the course together, and most sellers publish only the course.

If you need results for a date, work backwards from the full course on the box rather than the "first results" claim.

Why strips sometimes seem not to work

When strips disappoint, it is usually for one of five reasons, and only one of them is the product.

1. The stain is not the kind strips reach well. Deep intrinsic staining can need far longer than one box.
2. The tooth is not natural. Crowns, veneers and fillings stay the colour they are.
3. The strip is not a bleaching product. Purple and surface-polish strips do not change the tooth's own colour.
4. The strip did not stay in contact. Crest's guidance notes that most strip instructions say not to brush just before applying, because it affects how well the strip sticks.
5. Expectations came from a shade number. Sellers' "shades whiter" figures come from their own studies, measured differently from brand to brand, so they are not a promise for your teeth.

Our step-by-step guide on how to use whitening strips covers the application mistakes in detail.

The side effects that come with them

Strips that bleach also bring the two side effects the evidence consistently reports: tooth sensitivity and gum irritation. The ADA says these are the most common adverse effects of whitening, and the Cochrane review found them more common at higher concentrations, though mild and transient.

The ADA says sensitivity with strips or trays may develop within two to three days of starting and usually resolves by the fourth day after treatment ends. Gum irritation usually comes from gel touching the gums, which is why careful placement matters. Crest's label tells users with significant sensitivity to stop for 2 to 3 days and discontinue if it persists. Our guide to whether whitening strips are bad for your teeth looks at enamel and sensitivity in more depth.

So, are they worth trying?

For an adult with healthy teeth, no crowns or veneers at the front, and general yellowing rather than one tooth darker than the rest, peroxide strips are a reasonable, inexpensive thing to try. For anyone with sensitive teeth, gum problems, visible restorations, or staining that appeared suddenly on one tooth, a dental check comes first.

Two options that pay us nothing are worth trying before you buy a kit. A professional clean removes surface staining, and the ADA says brushing with a whitening toothpaste can reduce a wide range of surface stains. Neither pays us anything. If you do decide to buy, our ranking of the best teeth whitening kits compares strips on what each seller discloses about its active ingredient and what a treatment costs.