Enamel has no nerve supply, which is why a healthy crown feels nothing. Dentine is threaded with microscopic tubules running toward the pulp — expose it, and a change in temperature moves the fluid inside them.

Exposed dentine — the layer directly under your enamel. Something has uncovered it, usually receding gums, acid erosion or years of hard brushing, and the fluid inside its microscopic channels now moves when cold or sweet reaches it. Healthy enamel has no nerve supply at all, which is why an intact tooth registers cold and feels nothing.

It is common, though how common depends on how you ask. A 2025 review in BMC Oral Health pooled 39 prevalence studies and landed on 32% (95% CI 27–37%) — while noting that the studies disagreed almost completely: “The statistical heterogeneity was very high among studies (I2 = 99.7%)”. The single biggest reason was method, not population. Surveys that actually examined every participant found more of it than surveys that asked people to self-report.

The mechanism, briefly

Dentine is not solid. It is threaded with millions of microscopic channels called tubules, running from its outer surface inward toward the pulp, where the nerve lives. Those tubules are full of fluid.

When exposed dentine meets something cold, sweet or simply a toothbrush, that fluid moves. The nerve endings at the inner end of the tubules detect the movement and report it as a short, sharp pain. That is the whole of it — the tooth is not damaged by the cold drink, it is reporting a pressure change through a channel that should have been covered.

This is why sensitivity is sharp and brief rather than dull and lingering. It is also why it comes and goes: what matters is whether the tubules are open.

What exposes dentine

Cause	What it looks like	What helps
Receding gums	Sensitivity at the gumline; teeth look longer; a notch you can feel with a fingernail	Stop the recession first — see what causes receding gums
Acid erosion	Generalised, often worse on the inside surfaces; teeth look glassy or thin at the edges	Cut how long the acid is in contact, and how often; brushing habits matter less than the diet
Abrasion from brushing	Wedge-shaped notches at the gumline, often worse on one side	Soft brush, light pressure, pen grip
Recent whitening	Started with treatment, affects many teeth at once, fades over days	Pause; it is usually temporary and reversible
A new filling or crown	One tooth, began after the appointment	Usually settles in a few weeks; tell the dentist if it does not
Grinding	Flattened biting surfaces, jaw ache on waking	A night guard; treat the grinding, not just the symptom
Decay or a crack	One tooth, getting worse, may hurt on biting	A dentist. This is not ordinary sensitivity

The distinction that actually matters

Ordinary sensitivity is sharp and stops within a second or two of the cold going away. That is a tubule problem and it is manageable.

Pain that lingers for thirty seconds or more after the stimulus, arrives unprovoked, wakes you at night, or hurts when you bite down is a different thing. That pattern suggests the nerve itself is inflamed or the tooth is cracked, and no toothpaste addresses either. Book an appointment rather than waiting it out — this is the one part of this page worth acting on today.

What sensitivity toothpaste actually does

There are two mechanisms on the shelf, and they work differently.

Potassium nitrate calms the nerve itself, making it less reactive to the fluid movement. It does not seal anything.
Stannous fluoride, arginine and similar physically block the open ends of the tubules. They also deposit fluoride, which is useful in its own right on exposed root.

Both need weeks of consistent use, not days. A 2019 analysis of 30 trials compared results at two, four and eight weeks, and some US labels say to stop and ask a dentist if “pain/sensitivity still persists after 4 weeks of use”. Trying a paste for four days is not a fair test. Use it as your ordinary toothpaste, twice daily, and judge it at the end of the month.

Choosing a toothpaste for it: toothpaste for sensitive teeth sets out which active works which way, what the trials measured, and who paid for them.

Hydroxyapatite pastes are marketed hard for sensitivity as well. Independent reviews found they helped over about four weeks, in few and short trials, and the most favourable review was co-written by a manufacturer’s employees — the sensitivity toothpaste guide sets that evidence beside the other actives, and does hydroxyapatite toothpaste work covers the rest of what it is sold for.

For one sore spot, there is a method with trial support: in a 2010 arginine trial, people put a pea-sized amount on the sensitive surface with a fingertip and massaged it for a minute, and their air and probe scores improved straight away compared with a plain paste. And do not rinse after brushing generally: England’s prevention toolkit advises spitting out rather than rinsing with water, to avoid diluting the fluoride — see is mouthwash bad for you? for more on that habit.

What makes it worse

Acid, more than the brushing that follows it Sipping acidic drinks slowly, or holding them in your mouth, does far more damage than the timing of your next brush — which turns out not to be well supported at all. See what causes enamel erosion. Rinse with water and get on with your day.
Pressure Hard bristles and a firm grip abrade the exact area that is already thin. If your brush splays within a month, that is your answer.
Repeated whitening Peroxide opens tubules temporarily. Occasional use is fine; back-to-back courses are not. See natural teeth whitening for what actually works.
Ignoring a dry mouth Less saliva means less remineralisation and more acid sitting around — dry mouth makes everything on this page worse.

See a dentist if

The pain lingers, wakes you, or comes without a trigger; one tooth is clearly worse than the rest; it hurts to bite; there is swelling; or a month of sensitivity toothpaste used properly has changed nothing. Sensitivity is common and usually benign, but it is also how a cracked tooth and an inflamed nerve announce themselves, and those get more expensive the longer they wait.

References

Survey methods contributing to the difference of dentin hypersensitivity prevalence: a systematic review and meta-analysis. BMC Oral Health 2025;25. DOI · PubMed · Funding: see ledger
Hu ML, Zheng G, Lin H, et al. Network meta-analysis on the effect of desensitizing toothpastes on dentine hypersensitivity. J Dent 2019;88:103170. DOI · PubMed · Funding: see ledger
Haleon US Holdings LLC. Sensodyne (potassium nitrate and sodium fluoride) toothpaste, Drug Facts label, as filed with the US Food and Drug Administration. DailyMed. Official page, accessed 23 Sep 2026.
Fu Y, Li X, Que K, et al. Instant dentin hypersensitivity relief of a new desensitizing dentifrice containing 8.0% arginine, a high cleaning calcium carbonate system and 1450 ppm fluoride: a 3-day clinical study in Chengdu, China. Am J Dent 2010;23(Spec No A):20A–27A. PubMed · Funding: see ledger
Office for Health Improvement and Disparities. Delivering better oral health: an evidence-based toolkit for prevention (chapter 2, summary guidance tables). Official page, accessed 23 Sep 2026. · Funding: see ledger

What causes sensitive teeth?