What to try when Sensodyne stops working: an ingredient-led guide to switching.

When Sensodyne stops working, the thing to try is the mechanism your tube never had, because the range is built on three different actives under one name. The way to try it is an eight-week test with one variable changed, judged against the clock the trials give each active, and the first job is to decide which of four different things "stopped working" means in your mouth. On the UK shelf, the one published ingredient list that carries a nerve active and an occluder together with fluoride is S3's (category review, September 2026).

What was checked23 peer-reviewed studies, S3 consumer trial (ADSL, 2026), product information as published by each brand, the Oral Health Foundation and the NHS

Which Sensodyne were you using, and what does that tube actually do?

Three different tubes answer to that name, and they do three different things. Based on what each brand states about its own formula, the Repair & Protect and Clinical Repair variants are built on calcium sodium phosphosilicate, a bioactive glass sold as NovaMin; Sensodyne Rapid Relief and Sensitivity & Gum on stannous fluoride; and Pronamel Daily Protection, Daily Care and Complete Protection+ on potassium nitrate, with the levels, fluoride salts and bases as published on the Boots product pages in September 2026. This page compares ingredients and stated actions only, not clinical performance, based on what each brand states about its own formula. Prices and formulations may change; always check the pack.

The active column is the whole guide. Potassium nitrate is a nerve-side active and does nothing to an open tubule; the glass and the stannous salt are occluders that narrow or plug the tubule and leave the nerve exactly as reactive as it was. Whichever row you were on, the other column is the mechanism you have not had. The brand's own FAQ is clear that its pastes work while you keep using them: Sensodyne states that if you stop brushing with its toothpaste, your sensitivity can return.

Read the pack you own, not the page: the brand's own FAQ and the retailer's ingredient list do not always agree on which fluoride salt a variant carries, and the list on the tube is the one that binds. The companion page that decodes the range goes through every variant's published list.

What does "it stopped working" actually mean?

It means one of four things, and each has its own test. Three of them are worth ruling out before you buy anything, because they are free, and the fourth is the only one an ingredient list can fix.

The table has a bias built in, and it is deliberate: three of its four rows send you away from the shelf. Sensitivity toothpaste is a self-managed category. In a 2026 qualitative study of eighteen Australian adults with confirmed dentine hypersensitivity, interviews rather than a trial, part of a research programme funded by a toothpaste manufacturer, nearly nine in ten had started a desensitising paste on their own initiative, none had been screened for the condition by a dentist, and half described a condition they were restricting their diet for as having no daily impact⁵. Many readers of this page will have arrived the same way, with nobody having checked that the paste was the right tool. The four rows are that check.

Did it ever do more than the placebo response?

Partly, and less than it felt. The honest starting point for anyone on potassium nitrate is that its effect is real and modest, and that the first weeks on any new tube include a response to being treated at all. In a six-week double-blind trial of 120 adults, a potassium nitrate paste, a strontium acetate paste and a plain fluoride paste all reduced sensitivity, with no significant difference between them at any point, and the plain fluoride group improved significantly from baseline on the cold-air test⁶.

The same Bristol group later showed how large the sensory part can be. In a split-mouth randomised study of 22 adults, a single application of a periodontal dressing over the sensitive teeth cut reported pain by 95% to a cold stimulus and 85% to a puff of air, and the authors concluded that the perception of pain in this condition is altered by sensory factors⁷.

Two things follow. A strong first fortnight on any paste is not evidence that the active worked, and a flat month is not proof that it failed. That is why the potassium reviews are cautious: the Cochrane review of six randomised trials found an effect on the air-blast and probe tests at six to eight weeks but none on the patients' own rating, and a 2000 review of 27 clinical trials records that the proposed mechanism has never been confirmed in intact human teeth and that some trials showed large placebo effects³⁸. Potassium nitrate has been in desensitising toothpastes since the 1970s and in placebo-controlled trials since the 1990s, which is a long time for a mechanism to stay unconfirmed and a long time for an effect to keep showing up.

When does each active start, and does it hold?

Each active has its own clock, and the trials have timed them. The clearest single comparison is an industry-funded double-blind trial of 120 adults, paid for by the maker of the stannous fluoride paste it tested, which ran a marketed potassium nitrate paste, a marketed stannous fluoride paste and an experimental oxalate paste against a plain fluoride paste for eight weeks, then put every group on the plain paste for three more¹. In that industry-funded double-blind trial all three actives beat the plain paste on the cold-air test from day three, but on the probe test potassium nitrate had not separated from the plain paste at day three and had by week two, while the two occluders had separated by day three; by week eight the improvement over the plain paste on the cold-air score was 57% for stannous fluoride, 47% for oxalate and 44% for potassium nitrate, and the three no longer differed significantly from one another¹.

Read the table for its shape rather than its winners. The occluders move first: at two weeks, a 2026 network meta-analysis of 93 randomised trials from a Bristol-led team, whose members have declared fees from toothpaste manufacturers in earlier work, puts stannous fluoride and arginine at the top, with the other classes, potassium nitrate and hydroxyapatite among them, showing small to moderate two-week effects at low certainty⁹. The nerve active moves later and keeps moving: a 2019 systematic review of 74 randomised trials that grouped every treatment by when its effect reached significance found potassium nitrate only in the long-term group, hydroxyapatite and stannous fluoride in the one-month group as well, and no toothpaste at all in the seven-day group, which held only in-office treatments². Twelve weeks is the longest any potassium nitrate toothpaste has been followed in the library behind this page, in a manufacturer-sponsored placebo-controlled trial of 67 adults where the 5% paste beat its placebo on touch, heat and air at six weeks and again at twelve, and was not measured earlier¹⁶.

So a reader on potassium nitrate who felt nothing at day three was on schedule, and a reader on the glass or stannous fluoride who felt something by day three was too; neither fact says anything about week eight. And the eight-week results in the industry-funded double-blind head-to-head trial were close enough that the actives no longer differed significantly, which is the honest version of "stronger"¹.

Does potassium nitrate stop working with continued use?

Nobody has tested it, as far as PubMed can tell, and this page will not pretend otherwise. A PubMed search in September 2026 for tolerance, tachyphylaxis, habituation or loss of efficacy with potassium toothpastes returned no trial of the question; the potassium trials run eight to twelve weeks and stop³¹⁶. What the eight-week trials do show is the opposite of a fade: in the industry-funded double-blind head-to-head trial the potassium nitrate benefit on both tests was larger at week eight than at week four, and the share of its users who were pain-free on at least one tooth rose from 7% at week four to 28% at week eight¹.

What has been measured is what happens when you stop. In the same industry-funded double-blind trial, three weeks in which every group brushed with the plain fluoride paste left the three active groups still significantly better off than the plain-paste group, keeping between two thirds and four fifths of the benefit they had at week eight, and level with one another at week 11¹. The only trial that has compared stop-start use with continuous use did it with the bioactive glass, not potassium: a manufacturer-funded 24-week randomised trial of 76 adults found that two eight-week courses separated by eight weeks on a standard fluoride paste gave the same small improvement in cold-air scores as brushing with the glass paste for the whole 24 weeks, and no change on the probe test with either regimen¹¹.

Two consequences. First, "it wore off" is the wrong model for a daily paste you are still using: under continued use the measured line rises to week eight, and after stopping it declines over weeks rather than falling off a cliff, as the washout data of the industry-funded double-blind trial show¹. Second, the brand and the charity agree on where the loss comes from. Sensodyne states that if you stop brushing with its toothpaste your sensitivity can return, and the Oral Health Foundation says the same of sensitive toothpastes in general, that you need to keep using them to maintain the effect¹⁷. If yours seems to have faded while you are still brushing with it twice a day, the routine and the mouth are the suspects, not tolerance.

If you were on potassium nitrate, what have you not tried?

An occluder. Potassium nitrate is the nerve-side active, and in the one trial that looked at both the mouth and the microscope, a four-week double-blind trial of 30 adults with a NovaMin-affiliated author, the 5% potassium nitrate paste beat a plain paste on the air and cold-water tests at four weeks while the companion electron-microscope test found it had occluded no tubules¹². One in vitro study points the other way: on etched dentine discs from 45 extracted premolars, a potassium nitrate toothpaste applied twice daily produced detectable tubule occlusion on the electron microscope by day 14, more than a potassium mouthwash or water¹⁸. Two bench protocols, two answers, and a 2000 review that calls the clinical mechanism of potassium unconfirmed in intact human teeth: this page does not resolve it, and neither should a label⁸. What the potassium reader has not had, on any reading, is an active whose job is the tubule.

The occluders have the stronger evidence at two weeks and a broad base at eight. In the 2026 network meta-analysis of 93 randomised trials, stannous fluoride carried a high-confidence two-week effect against a fluoride paste and arginine a similar effect at low confidence⁹. A 2023 network meta-analysis of 32 randomised trials by an overlapping and manufacturer-affiliated Bristol team, whose authors declare past fees and grants from toothpaste makers, recommended stannous fluoride, potassium with or without stannous fluoride, and arginine, all used twice daily¹⁹. Against placebo, a 2015 meta-analysis of 31 randomised trials found significant effects for stannous fluoride, the glass, arginine and potassium alike, each with a wide interval that overlapped the others²⁰. The 2020 network meta-analysis of 125 randomised trials ranked calcium sodium phosphosilicate first of the single formulations on every stimulus it pooled, tactile, cold and air²¹.

Which occluder is a smaller question than whether you keep the potassium. Moving from a potassium paste to a glass or stannous paste is a swap: you gain the tubule and give up the nerve. Keeping both means a water-based paste. S3 Sensitivity Science™ is one: its water base is what lets potassium nitrate and hydroxyapatite share the tube, which a water-free formula built around bioactive glass cannot do. The pairing that exists on the UK shelf is potassium nitrate with hydroxyapatite, and it exists once: of the 51 UK sensitivity toothpastes whose published ingredient lists the category review read in September 2026, only S3 lists potassium nitrate, hydroxyapatite and a fluoride salt together. S3 keeps the potassium nitrate at 5%, the dose the placebo-controlled trials used.

If you were on the bioactive glass or stannous fluoride, what have you not tried?

A nerve active. A glass or stannous paste works on the route the trigger takes; it does nothing to how readily the nerve fires once a signal arrives. Occluding and desensitising are two jobs, neither active does the other's, and a formula built for sensitivity carries both. If your occluder has stopped keeping up after a fair run, the gap is more likely the nerve than the plug, and the plug itself wears: in a randomised trial of 45 patients, hydroxyapatite applied by a dentist reduced sensitivity more than water or nothing at every check from the first day to the fourth week, and at the eighth week the four groups had converged¹⁵.

The evidence for adding potassium to an occluder is the evidence for the combination. In the 2020 network meta-analysis of 125 randomised trials, the pairing of potassium with hydroxyapatite carried large effects against fluoride toothpaste for both touch and air at moderate to high certainty, and potassium on its own was listed for touch alone²¹. In an eight-week double-blind trial of 85 adults sponsored by the maker of the nano-hydroxyapatite pastes it tested, a 10% nano-hydroxyapatite paste with 5% potassium nitrate reduced cold-stimulus sensitivity more than the same paste without potassium at weeks two, four and six, and matched the calcium sodium phosphosilicate comparator at every fortnight¹⁴. The 2026 network meta-analysis did not report that pairing in its abstract, so the combination's case rests on the 2020 analysis and single trials, and this page says so rather than borrowing the stannous fluoride confidence rating for it⁹²¹.

The water-base point applies in reverse. Bioactive glass needs a water-free base, and the two UK stannous variants are also water-free on their ingredient lists, so within this range the potassium option lives in different, water-based tubes. S3 was formulated for this reader: for people whose current sensitivity toothpaste worked at first and then stopped, and for sensitivity from gum recession, where exposed tubules and a reactive nerve are both in play.

Where does S3 sit if you are switching?

In the one tube on the UK shelf that carries both mechanisms. S3 Sensitivity Science™ pairs 5% potassium nitrate with two hydroxyapatites and 1450 ppm fluoride in a water base, and the water base is the reason the pairing is possible, since the glass variants and the UK stannous variants are built without water. For the reader on Repair & Protect that means adding the nerve active without giving up an occluder; for the reader on Pronamel or Daily Care it means keeping the potassium and adding the tubule work.

It runs on the same clock as the trials above: S3 starts working from the first brush and is judged at two to four weeks, not at day three. It is sold direct from the brand rather than at Boots or Superdrug, and every ingredient list behind that "one tube" sentence, with its source and read date, is on the category review.

How do you run a fair eight-week switch?

Borrow the trial protocol and run it on yourself. The 1997 consensus guidelines for sensitivity trials ask for a tactile, a cold and an evaporative stimulus, a negative and a benchmark control, eight weeks for most trials, and a follow-up to see whether the change persists⁴. You cannot blind yourself and you have no control group, which is exactly why the placebo evidence above matters, but you can hold everything else still.

• Change one thing. New tube, same brush, same technique, same time of day, no new mouthwash, no whitening paste alongside.
• Pick two triggers you meet anyway, a cold drink from the fridge and a breath of cold air, or the toothbrush on the gumline, and note them at the same point each week.
• Spit, do not rinse, twice a day, and keep an hour between anything acidic and the brush; the Oral Health Foundation lists those as the habits that let a sensitivity paste work, and hard brushing and rinsing as the ones that undo it¹⁷.
• Expect little at day three from a nerve active and something from an occluder, a first reading at week two, a fair one at week four, and the verdict at week eight, because those are the checkpoints of the industry-funded double-blind head-to-head trial and of the 2019 systematic review¹².
• Judge the eighth week against the first, not against the best day in between.

Potassium accumulates around the nerve over weeks and mineral is laid down brush by brush, which is why S3 is judged at two to four weeks and never at two to four days. The companion page on how long to give a new paste sets out what each fortnight should feel like, and the Journal's page on how sensitive toothpastes work and why yours might not be working explains the two mechanisms from the other direction.

When is switching the wrong answer?

When the pain has changed character, and when the mouth has. The Oral Health Foundation's four reasons to see a dentist rather than the shelf are severe pain, sensitivity that has lasted more than a few weeks, a single affected tooth, and pain that came on suddenly, any of which can point to decay, a cracked tooth, gum disease or infection¹⁷. The NHS puts a plain time limit on toothache: see a dentist if it has lasted more than two days²².

UK guidance for dentists says the same from the other side. The 2017 UK Forum guidelines for general practice, a review written for dentists, state that there does not currently appear to be one ideal desensitising agent, and that treating the condition depends on the dentist and the patient changing the patient's behaviour together²³. That is a polite way of saying that a third tube is not a plan. A dentist can apply a desensitising treatment or a bonding agent to the tooth, recommend a high-fluoride paste, cover a worn root surface or treat the gum¹⁷. In a practice-based randomised trial of 75 UK patients, a bonding agent applied by the dentist gave the largest reduction in air-blast sensitivity at two weeks and at six months, ahead of a desensitising toothpaste that itself kept improving over the six months²⁴.

So the order is: rule out the four reasons, fix the routine, then switch mechanisms, and give the switch eight weeks. Switching first and asking later is how people end up on their fourth Sensodyne with the same active as the first.

Frequently asked questions

Should I try a different Sensodyne variant first?

Only if it moves you across the table, and it can. Based on what the brand states, going from Pronamel Daily Protection, Daily Care or Complete Protection+ to Repair & Protect, Clinical Repair, Sensodyne Rapid Relief or Sensitivity & Gum changes the mechanism from nerve to tubule, and the reverse move changes it back; moving between two potassium variants, or between the glass and the stannous variants, keeps you on the same side. What no move within the range gives you is both mechanisms in one tube, because the occluding variants sit in water-free bases and the potassium variants in water-based ones.

Does potassium nitrate stop working over time?

No trial has tested it, and the Cochrane review of six trials takes its potassium readings at six to eight weeks of continuous use³. In the industry-funded double-blind head-to-head trial the potassium nitrate benefit was still rising at week eight, and the measured fade came only after stopping, slowly: most of the benefit remained three weeks after every group went back to a plain paste¹. If it seems to have faded while you are still brushing with it, look at the routine and the mouth before the tube.

How long after stopping does sensitivity come back?

Slower than "wore off" suggests, on the one trial that timed it. Three weeks after the potassium nitrate, stannous fluoride and oxalate groups switched to a plain fluoride paste they still kept roughly two thirds to four fifths of their week-eight benefit and remained significantly better off than the group that had used the plain paste throughout, in an industry-funded double-blind trial of 120 adults¹. Beyond three weeks nobody has measured it for a potassium toothpaste, and this page will not invent a number. The companion page on what happens when you stop a potassium nitrate paste goes further into the mechanism.

Is hydroxyapatite better than the glass I was using?

Not on the published comparison, and this page will not say it is. In vitro, on dentine discs, a 15% nano-hydroxyapatite paste closed about 98% of tubules against about 83% for a calcium sodium phosphosilicate paste, and the gap was not statistically significant²⁵. In the eight-week double-blind trial of 85 adults sponsored by the nano-hydroxyapatite maker, the 10% and 15% pastes, with or without potassium nitrate, were as effective as the glass, and no more¹⁴. The reason to move to hydroxyapatite is the tube it can share: potassium nitrate alongside it in a water base, which the glass cannot offer.

What does S3's formulation scientist say about sensitivity coming back after stopping?

That the first questions are about what replaced the paste, not the paste. Is the product you moved to more abrasive, with a higher relative dentine abrasivity (RDA); is its pH different; has your diet changed. Those three are the same checks as the routine row of the table above, and they come before any conclusion about the active.