Whitening strips and sensitive teeth: what to know before you start.

Whitening strips sold in UK shops may carry no more than 0.1% hydrogen peroxide, or use a peroxide-free agent such as PAP, so they are not the strips that the published sensitivity trials tested¹. Those trials used strips with 3% to 10% hydrogen peroxide, and with sensitive teeth the better first step is a dental examination, which is where the reason for the sensitivity gets found²³⁶. In a 2020 meta-analysis of randomised trials, peroxide strips caused sensitivity less often than dentist-supervised home trays (risk ratio 0.78) and produced a smaller colour change, one its authors judged too small for the eye to see⁴. No published trial has tested a strip at the UK legal strength, or a PAP strip, for sensitivity in people, and none that this page could locate describes recruiting people because they already had sensitive teeth. S3 Sensitivity Science™ is a toothpaste, not a strip, and its published ingredient list contains no peroxide and no PAP: its actives are potassium nitrate and two forms of hydroxyapatite, with 1450 ppm fluoride.

What was checked23 peer-reviewed studies and reviews, UK legislation, four OPSS product safety reports, two ASA rulings and CAP advice, the NHS and the Oral Health Foundation, and product information as published by each brand

What is in a whitening strip sold in the UK?

A very small amount of hydrogen peroxide, or an agent that is not hydrogen peroxide at all, because the law limits what a shop may sell¹. The cosmetics regulation that applies in Great Britain allows oral products, tooth whitening products included, to contain or release no more than 0.1% hydrogen peroxide¹. Tooth whitening products above 0.1% and up to 6% may be sold only to dental practitioners; each course starts with a first use by or under a dentist, and they are not to be used on anyone under 18¹. Who may carry out whitening, and what counts as illegal practice, is set out on the page on whether tooth whitening is legal in the UK.

So the boxes on a shop shelf fall into a few groups. Some strips and pens list hydrogen peroxide without a level. Others use phthalimidoperoxycaproic acid, written PAP on the front of the pack. Some older products used sodium chlorite¹⁷²². And colour correctors do not bleach at all: they tint the tooth surface so that yellow looks less yellow. Whitening toothpastes are a separate subject, covered on the page on whitening toothpastes and sensitivity.

The Oral Health Foundation says shop-bought strips, gels and paint-on products may remove some surface stains but usually do not change the natural colour of teeth much, and that they hold only a very small amount of whitening ingredient⁶. The NHS page on teeth whitening goes further: a kit from a pharmacy or online does not work as well as treatment by a dental professional and may harm the teeth and gums⁵.

The table below lists five products read on their UK product pages in September 2026, based on what each brand states about its own formula. This page compares ingredients and stated actions only, not clinical performance. Prices and formulations may change, always check the pack.

Do whitening strips hurt sensitive teeth?

In the trials, a minority of people using peroxide strips reported sensitivity, but every one of those trials used 3% hydrogen peroxide or more, and none is described as picking its volunteers for having sensitive teeth²⁴. What the trials can speak to is the difference between strips and other ways of bleaching, and how often people whose teeth were not already sensitive felt it.

The best summary compares strips with bleaching supervised by a dentist. A 2020 systematic review and meta-analysis of 20 randomised trials found that strips carried a lower risk of tooth sensitivity than dentist-supervised home trays (risk ratio 0.78, 95% CI 0.65 to 0.93) and a lower intensity, with the evidence graded moderate⁴. In the meta-analysis the trays produced a larger colour change on the spectrophotometer, a difference the authors describe as undetectable by the unaided eye, and only two of the 20 studies were at low risk of bias⁴. The dentist-led route is not the painless one. In this comparison it was the one that hurt more often.

A 2024 network meta-analysis of over-the-counter bleaching trials, covering 37 studies and 1,932 people, found the largest colour change with 6% hydrogen peroxide strips worn for 14 hours or more in total². The lowest risk of sensitivity in that analysis came with a 10% carbamide peroxide gel worn seven to 13 hours and with placebo, and the authors rated the certainty of the evidence as low².

Two trials gave some people placebo strips with no peroxide in them. In a trial of 54 adults with a dummy strip, run double-blind, funding unknown, minor sensitivity showed up in 11% on the dummy and 12% on the 9.5% peroxide strip⁷. In a randomised trial of 80 adults by authors employed by Procter & Gamble, 10% reported sensitivity after a year of 6% strips worn five minutes a day against 5% on placebo, a difference that was not statistically significant, and the two people who stopped because of sensitivity were both on the peroxide strip⁸. None of that means the ache on a peroxide strip is imagined. These trials logged sensitivity as a side effect rather than testing it as an outcome, and neither abstract says how bad it was.

The larger numbers come from the strip maker's own programme. Pooled data from seven randomised trials at one dental school, analysed by authors employed by Procter & Gamble, put tooth sensitivity at 20% and oral irritation at 22% among 148 people using 6% strips twice a day for two weeks, and one person stopped early⁹. In an earlier randomised trial of 34 adults, also by authors employed by Procter & Gamble, 13% reported sensitivity with 6% strips worn for an hour a day over a week, against 22% with a 5% carbamide peroxide tray gel that contained potassium nitrate and was worn for six to eight hours a day¹⁰.

One trial held the peroxide steady and changed only the way it was delivered. In a randomised trial of 50 patients using 10% hydrogen peroxide for seven days, strips and custom trays gave the same colour change, and sensitivity was recorded less often with strips, 50.2% against 70.2%³. In the same randomised trial the mildest score, though, turned up more often with strips (37.3% against 20.9%), and the authors concluded that the peak level of pain was higher with them³. Each arm of that randomised trial had 25 people in it, so a figure such as 50.2% is not a head count, and the abstract leaves unexplained what it is a proportion of³.

A newer trial built a desensitiser into the strip. In a double-blind randomised trial of 96 participants, a 3% hydrogen peroxide strip with 1.5% potassium nitrate gave the same colour change as a plain 3% strip, and the abstract describes no discernible sensitivity with it after 28 days against some obvious sensitivity with the plain strip, without putting numbers on the gap¹¹. Even the strip in that randomised trial carried 30 times the hydrogen peroxide a UK shop may sell¹¹¹.

In the laboratory, peroxide from a strip gets inside the tooth. Strength counted on the bench: a 14% strip pushed more peroxide through extracted incisors into the pulp space than a 6.5% one did, in a laboratory study¹⁴. Another laboratory test found hydrogen peroxide inside the pulp chamber after two shop peroxide strips, most of all after a 6% home gel, and none after a peroxide-free strip¹³. Neither laboratory study measured pain, and a tooth on a bench is not a person¹³¹⁴. Why peroxide in the pulp is thought to cause the ache is explained on the page on why whitening makes teeth sensitive.

Why do the trials not describe the strips in your basket?

Because the strips they tested were stronger than anything a UK shop may sell, and the products a shop does sell have barely been tested in people¹². A 2024 scoping review of 88 studies found that the clinical support for over-the-counter whitening rests mainly on strips, while toothpastes, rinses and trays were backed mostly by laboratory work, and that tooth sensitivity and gum irritation were the main side effects¹⁶. The strips behind that clinical support were peroxide strips.

This page searched PubMed three ways in September 2026. The first search combined terms for PAP, phthalimidoperoxycaproic acid, peroxide-free and non-peroxide agents, sodium chlorite and the UK legal limit with strips, whitening or bleaching, with sensitivity, and with trial terms. It returned fifty-one records, most of them from other fields of medicine, and none was a randomised trial of a PAP strip, or of a strip at the UK legal strength, in people.

One trial of a peroxide-free strip in people did turn up. In a double-blind randomised trial of 50 adults, written and funded by Procter & Gamble, a peroxide-free strip, paste and rinse regimen left tooth colour where it started over 14 treatments while the company's own peroxide strip changed it, and minor sensitivity and irritation were the commonest findings in both arms, without a count for either¹². A search for phthalimidoperoxycaproic acid on its own returned ten records: laboratory studies, reviews and one small clinic study of a PAP gel activated by a laser, with no trial of PAP used at home by people.

The second search, for strips with dentine hypersensitivity or sensitive teeth, returned three records, and none of them is described as recruiting people because they had sensitive teeth. One was the 2024 network meta-analysis above². Another was the potassium nitrate strip trial, whose abstract does not give its recruitment criteria¹¹. The third was about a strip for treating sensitivity, not for bleaching.

The third search, for strips with desensitising agents, potassium nitrate, dentifrice or toothpaste, and sensitivity, returned eleven records. None tested a sensitivity toothpaste brushed alongside strips. The nearest were the 2002 comparison with a tray gel containing potassium nitrate, by authors employed by Procter & Gamble, and the 2026 strip with potassium nitrate inside it, and neither put a toothpaste next to a strip¹⁰¹¹.

Who paid for the research matters as well. Four of the nine studies in people in the table were written by authors employed by Procter & Gamble; of the other five, two declare public funding or no conflicts and three carry no funding statement in their records^7891012. None of this means that a UK strip causes sensitivity, or that it does not. What it means is that the published trials answer a different question from the one on the box.

What do we know about PAP, peroxide-free strips and colour correctors?

Only what laboratory studies show, and they point in different directions¹⁷²⁰²¹. No published trial has put a PAP strip on people's teeth and asked whether it hurt.

A laboratory study of shop-bought products from the UK tested five non-hydrogen-peroxide whitening products from two major British outlets on extracted teeth¹⁷. Under the electron microscope several left a distinct etching pattern on the enamel, and two significantly reduced its microhardness in laboratory testing¹⁷. In that laboratory study two lightened the teeth less than saline and two more than a dentist's 10% carbamide peroxide gel, and the authors judged lightening most likely with sodium chlorite-based products¹⁷. That spread is not an argument for or against any single box on a shelf today, and those products were bought before the laboratory study appeared in 2019¹⁷.

In a German laboratory study of 60 coffee-stained teeth, whose first author went on to develop a PAP whitening set and form a company, a manufacturer interest the paper declares, PAP and sodium chlorite at most removed the stain, and only hydrogen peroxide lightened the teeth beyond their colour before staining¹⁸. The case for PAP being gentle on enamel comes partly from the company behind one PAP range: in a laboratory study written by two employees of that company, a PAP gel did not erode enamel or lower its microhardness over six ten-minute applications, while 6% and 35% hydrogen peroxide gels did¹⁹.

Two independent laboratory studies also found little enamel change with PAP, and disagreed about colour²⁰²¹. One, an in vitro study on extracted incisors, found that a PAP product lightened teeth about as much as a 37.5% hydrogen peroxide in-office gel²⁰. The other, an in vitro study on enamel samples, found that an over-the-counter PAP gel stopped improving after 14 days and did less than a dentist's 10% carbamide peroxide gel, which kept improving to day 28²¹.

Peroxide-free strips did worst on colour in laboratory tests. In one study two non-peroxide strips changed colour no more than water did while a peroxide strip changed it several times as much, and none of the three eroded enamel¹⁵. In another, a peroxide-free strip changed colour less than two peroxide strips¹³. In a trial in people of a sodium chlorite gel, an examiner-blinded randomised trial of 60 volunteers, two weeks of use gave only a small improvement in colour, and the spectrophotometer picked up no significant change²².

Colour correctors are a different idea, since they tint the tooth rather than bleach it, and the brand page in the first table describes its serum as designed to conceal yellow tones temporarily, on the surface.

The advertising regulator has looked at both kinds of product. The CAP advice on teeth whitening says marketers must hold evidence for performance claims and must not claim long-term results when their evidence shows only short-term whitening or temporary colour correction²³. In 2021 the Advertising Standards Authority upheld complaints about social media ads for a whitening kit pairing an LED light with a PAP formula, which described it as clinically tested and as proven, and as working 2.2 times faster than traditional whitening²⁴. The ASA found that one clinical trial had tested the whitening ingredient rather than the product itself and had no control group, that another tested a different product, and that a study on the product in people was neither blinded nor controlled; it ruled the claims unsubstantiated and misleading²⁴. One of the ads also carried a line about whiter teeth without sensitivity, and that line was not a separate issue in the ruling²⁴.

In 2024 the ASA upheld complaints about ads for a purple colour-correcting serum that showed stained teeth turning white on contact²⁵. Most of the evidence came from tests by its developer, whom the advertiser's website described as a scientific advisor, run on the author and one other person, and the sources themselves said the effect lasted several hours²⁵. The ASA found the claims, as consumers would understand them, unsubstantiated²⁵. One of those ads also said colour correction caused zero sensitivity; the complaints were about whitening, and the ruling did not assess that line²⁵.

What about whitening pens, gels and kits bought online?

They are where UK regulators have found peroxide far above the legal limit: a gov.uk search in September 2026 listed four product safety reports on tooth whitening products, each for peroxide above the legal limit, measured or declared^26272829. The search used the gov.uk search service, filtered to product safety alerts, reports and recalls, for teeth, whitening and hydrogen peroxide; all four reports came from local Trading Standards.

Buying online adds a second problem, which is the label. In a 2023 cross-sectional study built on test purchases of high-peroxide home whitening gels found through web searches, every online listing had an incomplete or missing ingredient list, one product arrived with no active ingredient in it, and in four others the peroxide measured ran from about 80% below the label to 9% above it³¹. In a laboratory study of products from a large online marketplace, the lowest-rated whitening serum caused severe changes to the enamel surface and the largest drop in microhardness, 14.2% against 8.84% in the untreated control, while the highest-rated strip performed about as well as a dentist-prescribed 20% carbamide peroxide gel³⁰.

In people, two other over-the-counter systems did less for colour than a dentist's gel. In a randomised trial of 39 adults, a paint-on gel and ready-filled trays whitened less than a dentist's 20% carbamide peroxide home gel and had lost colour by six months, though they also caused less sensitivity; neither system's strength was published by its maker³². Many people meet these products through video, and in a 2020 cross-sectional analysis of 100 YouTube videos on teeth whitening, 12% carried good-quality information while the poor-quality videos drew more views³³.

Does S3 contain any of the agents strips use?

No. S3 is a daily toothpaste, and its published ingredient list has no hydrogen peroxide, no carbamide peroxide, no PAP and no sodium chlorite. Its declared actives are potassium nitrate at 5%, nano-hydroxyapatite and biomimetic hydroxyapatite at 10% and 5% as solution, with sodium monofluorophosphate giving 1450 ppm fluoride. The active hydroxyapatite content is lower than those inclusion levels, and S3 states both.

Each of its three actives is aimed at everyday dentine sensitivity: potassium calms the nerve, nano-hydroxyapatite works inside the tubule, and biomimetic hydroxyapatite works on the surface. Sensitivity during bleaching is thought to arise differently, and a result for one is not evidence about the other.

No trial has tested any toothpaste, S3 included, as a way to make strips hurt less, and none has tested S3 alongside a strip at all.

If you have sensitive teeth, what should you do before starting, and if strips hurt?

See a dentist before the first strip, because the examination is where the cause of the sensitivity is found, and stop the strips if they hurt.

Sensitivity is a symptom with several possible causes, among them gum recession that leaves the root exposed, worn enamel, a cracked tooth and decay, and a strip cannot tell you which one you have. The Oral Health Foundation advises speaking to the dental team before whitening, so that they can make sure it is safe⁶. The NHS says whitening is not done on anyone aged 17 or younger or on unhealthy teeth or gums, and is not recommended during pregnancy or breastfeeding⁵. The own-label strip in the first table tells people with gum problems not to use it, and to stop if they feel pain or excessive sensitivity. The Journal's page on why teeth suddenly become sensitive goes through the causes a dentist will look for.

If strips sting, stop, and do not move on to a stronger kit or wear them for longer. The NHS tells people to talk to their dentist about whitening side effects that bother them⁵. An ache that stays after the strips have stopped, pain in one tooth, or pain that wakes you at night is a reason to book an appointment, not to try a different box.

A dentist-led course is the other route. What a dentist can adjust is laid out on the hub page on how to whiten sensitive teeth, chair-side and home-tray bleaching are set against each other for sensitivity on the page on in-chair whitening versus home trays, and the Journal's article on sensitive teeth after whitening deals with what happens once a course has finished.

Frequently asked questions

Are PAP strips better for sensitive teeth?

Nobody knows yet. No published trial has put a PAP strip on people's teeth and asked whether it hurt, so the idea that PAP spares sensitive teeth rests on laboratory work and on what brands say. In independent laboratory studies PAP changed enamel little, and in one of them an over-the-counter PAP gel lightened teeth less than a dentist's 10% carbamide peroxide gel²⁰²¹.

Can I use whitening strips if I have receding gums?

Ask a dentist first. Receding gums leave root surfaces exposed, and the Oral Health Foundation advises speaking to the dental team before any whitening so they can check it is safe⁶. The own-label strip in the table above tells anyone with gum problems not to use it.

What should I do if whitening strips make my teeth hurt?

Stop using them, and do not switch to a stronger kit or wear the strips for longer. If the ache has not gone within a few days of stopping, or it sits in one tooth, book a dental appointment; the NHS tells people to talk to their dentist about whitening side effects that bother them⁵. No trial has tested a toothpaste as a remedy for strip pain.

Does S3 contain peroxide or PAP?

No. S3's published ingredient list contains neither hydrogen peroxide nor PAP; its actives are potassium nitrate and two forms of hydroxyapatite, with 1450 ppm fluoride. No trial has tested S3, or any other toothpaste, alongside strips.

Are strips bought from abroad or online stronger?

Some are, and a product like that may not legally be sold to the public in the UK. UK product safety reports list a whitening pen sold via eBay with 7.32% hydrogen peroxide and a kit releasing 11%, both taken off the market, against a 0.1% limit for oral products²⁹²⁶¹. Test purchases of whitening gels online have also found peroxide levels far from what the label said³¹.