Why are my teeth sensitive?

Almost always because the dentin, the layer beneath the enamel, has become exposed. Dentin has microscopic channels (tubules) that connect to the nerve, so when enamel wears down or the gum recedes, cold or sweet moves the fluid in those channels and you feel the twinge. The most common causes are enamel wear, gum recession, bruxism and aggressive brushing.

Does sensitivity after whitening go away?

Yes. Sensitivity after whitening is normal and temporary: it usually lasts one to three days and clears on its own. The peroxide triggers a passing response in the nerve without harming the tooth. Using a toothpaste for sensitive teeth before and during the process helps. If the pain lasts longer than a few days or settles in a single tooth, have your dentist check it.

What toothpaste should I use for sensitive teeth?

A toothpaste for sensitive teeth, which works in two ways: potassium nitrate calms the nerve, while stannous fluoride or arginine seals the dentin tubules. Both need continued use before you notice the effect. Follow the directions on the package, and when brushing at night, spit but do not rinse with plenty of water so the active ingredient keeps working.

Is it normal for my teeth to hurt with cold?

A brief twinge with cold that comes and goes within seconds is typical of sensitivity from exposed dentin and is usually harmless. What is not expected is pain that lingers half a minute or more after the cold is gone, appears on its own or wakes you at night. That pattern points to the nerve and should be checked.

When is sensitivity serious?

When the pain is localized to a single tooth, lingers after the cold is removed, appears spontaneously or at night, or hurts on biting at a specific spot. Also if it is a new, marked sensitivity near a visible cavity or an old restoration. Those signs can indicate a cavity, a crack or nerve inflammation, and they need a dentist's evaluation.

Can tooth sensitivity be cured?

In most cases it improves greatly once the cause is treated. Mild sensitivity usually eases at home with desensitizing toothpaste, a soft brush and care with acids. When there is heavily exposed dentin, bruxism or gum recession, in-clinic treatment (fluoride varnish, sealing the neck of the tooth, a nightguard) targets the origin. The sooner the cause is identified, the simpler it is to resolve.

2026-07-20 · 7 min

Tooth sensitivity: why it hurts and what to do

Tooth sensitivity is one of the most common reasons people come to see me, and it almost always arrives with the same sentence: "I get a sharp twinge with cold and I don't know why." The good news is that in most cases it is treatable and has an identifiable cause. The flip side is that sometimes that twinge is a tooth's way of warning you that something more is going on. Here is how to tell the two apart.

What tooth sensitivity actually is

The technical term is dentin hypersensitivity, and it describes the problem well. Your teeth have three layers: enamel on the outside, dentin in the middle and the pulp (the nerve) at the core. Dentin is not solid. It is crossed by thousands of microscopic channels, the dentinal tubules, that connect the surface of the tooth to the nerve. As long as enamel and gum cover the dentin, those tubules stay sealed and you feel nothing. The trouble starts when the dentin becomes exposed.

Once those tubules are open, a stimulus on the surface (cold, heat, a light touch) moves the fluid inside them, and that movement fires the nerve endings connected to the pulp. This is known as the hydrodynamic theory, and it explains why the discomfort is a quick, sharp twinge that comes and goes almost instantly rather than a dull, constant ache. It is the fluid inside the tooth that carries the stimulus, not direct contact with the nerve.

Why teeth hurt with cold, sweet or acidic foods

Teeth that hurt with cold are the most common complaint, and there is a physical reason. Cold contracts the fluid inside the tubules, which creates a sudden movement the nerve reads as pain. That is why ice cream, cold morning air or a glass of iced water sets off the discomfort within seconds.

Sweet and acidic foods work through a slightly different mechanism: they change the concentration of particles at the surface of the exposed dentin and also drive fluid movement in the tubules. Heat can hurt too, though it tends to be less common in simple sensitivity. The key is the pattern. In dentin hypersensitivity the discomfort is brief, it is set off by a specific stimulus and it fades once the stimulus is gone. When the pain lingers or changes character, that is a different story, and we will come to it.

The most common causes

Sensitivity does not appear out of nowhere. There is almost always a reason the dentin became exposed. These are the ones I see most often in the clinic.

Enamel wear. Enamel thins from friction, from clenching or from dietary acid. When it wears down, the dentin underneath is exposed. Frequent acidic drinks wear the enamel silently, and many people never connect them to their sensitivity.
Gum recession. When the gum recedes, it uncovers the root of the tooth, which has no enamel and leaves the dentin directly open. It is one of the most common causes of sensitivity in adults, especially around the neck of the tooth.
Bruxism. Clenching or grinding wears the enamel and overloads the necks of the teeth, exposing dentin. If you wake up with a tense jaw or your dentist has noticed wear facets, it is worth ruling out: I go into it in what bruxism is.
Aggressive brushing. Scrubbing too hard or using a hard-bristled brush erodes enamel and contributes to gum recession. Many people confuse force with cleaning and get the opposite result.
After whitening. This is a transient, expected sensitivity, and it deserves its own section.

Sensitivity after whitening

This is the question I get most, so it is worth being clear: feeling sensitivity after a whitening treatment is normal and temporary. The whitening agent (peroxide) passes through the enamel and dentin and triggers a passing response in the pulp. It does not mean the tooth has been damaged or that the enamel has been permanently weakened.

It usually shows up during treatment or in the hours that follow, and it settles within one to three days. To make it easier: use a toothpaste for sensitive teeth for a few days before and during the process, avoid very cold or very hot drinks while it lasts, and do not stack sessions if the discomfort builds. If your whitening is supervised, the concentration or timing can be adjusted to make it more comfortable. I explain how the process works and how to reduce this discomfort in how to whiten your teeth. If the sensitivity lasts beyond a few days or turns into a localized pain in a single tooth, that is no longer expected and should be checked.

What you can do at home

Much of mild to moderate sensitivity improves with simple changes at home. The first is the right toothpaste. Toothpastes for sensitive teeth work in two different ways, and it helps to know which one you are looking for.

Potassium nitrate. It acts on the nerve: potassium ions diffuse through the tubules and lower the excitability of the nerve endings, so the stimulus arrives muted. It needs continued use to take effect and is not immediate.
Stannous fluoride or arginine. These work by sealing the tubules, physically plugging the channels so the stimulus does not reach the nerve. Fluoride also strengthens enamel against acid; if you are curious how, I cover it in what fluoride is for.

With either one, always follow the directions on the package. One trick that helps: after brushing at night with a potassium nitrate toothpaste, spit but do not rinse with plenty of water, so the active ingredient keeps working. Beyond toothpaste:

Use a soft-bristled brush and do not press hard: plaque comes off with technique, not force.
Do not brush right after anything acidic (citrus, wine, fizzy drinks). The enamel is briefly softened, and brushing it then wears it down more. Wait at least half an hour and rinse with water in the meantime.
If you notice you clench during the day, a conscious reminder to keep your jaw relaxed helps more than it sounds.

When sensitivity is a sign of something more

This is the part that really matters. Most sensitivity is harmless, but there are signs that set it apart from a problem that needs treatment. Pay attention if any of these appear:

Pain localized to a single tooth, rather than a diffuse discomfort across several areas.
Pain that lingers after the cold stimulus is removed, instead of fading within seconds. Discomfort that hangs on for half a minute or more points to the nerve.
Spontaneous or night pain, that appears with nothing triggering it or that wakes you at night.
Pain on biting or chewing at a specific spot, which can indicate a crack in the tooth.
New, marked sensitivity in a tooth that was fine before, especially if there is a visible cavity, an old restoration or the tooth has changed color.

These signs can point to a cavity, a crack, an exposed root with damage or an inflamed nerve (pulpitis), and none of them resolve on their own. If you recognize any of them, do not mask it with desensitizing toothpaste: book an evaluation. The sooner the cause is identified, the more conservative the treatment.

How we treat it in the clinic

When sensitivity does not settle at home, or when there is an underlying cause, the approach in the clinic starts with diagnosis: which tooth, which stimulus and since when, and ruling out cavities or cracks. From there, the options depend on the case.

For hypersensitivity from exposed dentin, we apply high-concentration fluoride varnish or desensitizing agents that seal the tubules, with a faster and longer-lasting effect than home toothpastes. When the exposed dentin is at the neck of the tooth and the loss is marked, that area can be sealed with a tooth-colored restoration. And when the cause is bruxism, treating the symptom alone is not enough: that is where a custom nightguard comes in to protect against the wear. When the origin is significant gum recession or a crack, it is assessed with the relevant specialist.

The common thread is that sensitivity responds better when the treatment goes to the cause and does not stop at the discomfort. That is why the first step is always understanding why it appeared.

If your teeth react to cold or sweet, start with the simple things: a toothpaste for sensitive teeth, a soft brush and less acid near brushing time. Give it a couple of weeks. If the discomfort eases, you are on the right track; if it does not settle, changes character or concentrates in a single tooth, that is the signal to have us take a look. Sensitivity almost always has a solution, and the sooner its origin is understood, the simpler it is to resolve.

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Written by

María Angélica Reyes

Oral Rehabilitation

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