A cavity hurts because decay has eaten through the hard outer layers of your tooth and reached the sensitive tissue underneath. The deeper the decay, the worse the pain. A small cavity may only sting when you eat something cold or sweet, while a deep one can throb constantly, even waking you up at night.
Understanding what’s happening inside your tooth explains the type of pain you’re feeling and how urgently you need to deal with it.
What’s Happening Inside Your Tooth
Your tooth has three main layers. The outermost is enamel, a hard shell that has no nerve endings at all. Beneath that is dentin, a softer layer riddled with microscopic tubes filled with fluid. At the center is the pulp, a bundle of nerves and blood vessels that keeps the tooth alive.
When a cavity is still in the enamel, you typically feel nothing. The trouble starts when decay breaks through into the dentin. Those tiny fluid-filled tubes react to temperature and sugar by shifting fluid rapidly toward the nerve endings deeper in the tooth. That fluid movement is what triggers the sharp, sudden zing you feel when you sip ice water or bite into candy. This is sometimes called a “hydrodynamic” response: it’s not heat or cold directly touching a nerve, but the physical pull of fluid across sensitive tissue.
If the decay keeps advancing and bacteria reach the pulp, the pain changes. The pulp becomes inflamed, a condition called pulpitis, and the nerves inside start firing on their own. That’s when pain stops being a reaction to something you ate and becomes a constant, throbbing ache that shows up uninvited.
Why the Type of Pain Matters
The kind of pain you’re experiencing tells you roughly how far the decay has progressed.
Sharp pain that stops quickly. If cold, sweet, or acidic foods cause a brief sting that fades within one to two seconds after you remove the trigger, the pulp is irritated but not permanently damaged. This stage is called reversible pulpitis. The tooth can still be saved with a standard filling, and the inflammation typically calms down once the decay is removed.
Lingering pain after a trigger. If the pain hangs around for minutes after you stop eating or drinking, or if heat rather than cold is the main trigger, the pulp is more seriously inflamed. This is irreversible pulpitis. At this point, a filling alone won’t fix it because the nerve tissue inside the tooth is dying. A root canal or extraction is usually the next step.
Spontaneous, throbbing pain. Pain that arrives on its own, without any food or temperature trigger, signals that the pulp is severely inflamed or already infected. This pain often throbs in sync with your heartbeat and can radiate into your jaw, ear, or neck.
Pain when biting down. If it hurts specifically when you chew or press your teeth together, the decay may have weakened the tooth structure enough to cause a crack. Research shows that pain on biting is associated with cracks that extend deeper into the tooth, run in multiple directions, or reach the root surface. People who grind or clench their teeth are more likely to experience this pattern.
When a Cavity Becomes an Abscess
Left untreated, bacteria from a deep cavity can push past the pulp and into the bone at the tip of the root, forming a pocket of pus called an abscess. This is an infection, and it comes with a distinct set of symptoms beyond ordinary tooth pain: severe, constant throbbing that may spread to your jawbone or neck, swelling in your face or cheek, tender lymph nodes under your jaw, fever, and a foul taste in your mouth.
Sometimes an abscess ruptures on its own, releasing a sudden gush of salty, bad-tasting fluid. The pain may temporarily drop, but the infection hasn’t resolved. An abscess doesn’t heal without treatment, and in rare cases the infection can spread to the throat, making it hard to swallow or breathe. Facial swelling combined with difficulty breathing or swallowing is a medical emergency.
Managing the Pain Until You’re Treated
Combining ibuprofen and acetaminophen is one of the most effective over-the-counter strategies for dental pain. These two drugs work through different mechanisms and can be taken together safely. A common combination tablet contains 250 mg of acetaminophen and 125 mg of ibuprofen, taken as two tablets every eight hours, up to six tablets per day. You can also buy the two medications separately and alternate them. Either way, this combination tends to outperform either drug alone for tooth pain.
A few other things can keep the pain from flaring while you wait for your appointment. Avoid very hot or very cold foods and drinks, since temperature changes drive fluid movement through exposed dentin. Chew on the opposite side of your mouth. If you can see a visible hole in the tooth, temporary filling material from a pharmacy can cover the exposed area and reduce sensitivity. Rinsing gently with warm salt water can help reduce inflammation around the gum line.
Signs You Need Urgent Care
Not every cavity warrants an emergency visit, but certain combinations of symptoms do. Pain that is severe enough to keep you from sleeping or eating, lasts more than a day, or comes with fever or visible facial swelling should be treated the same day if possible. If swelling makes it difficult to swallow or breathe, go to an emergency room rather than waiting for a dental office to open.
A lost filling or crown should be seen within a day or two, since the exposed tooth structure is vulnerable to rapid further decay and sensitivity. A large crack that exposes the inner layers of the tooth also needs prompt attention to prevent infection from setting in. If you’re unsure whether your situation is urgent, the simplest rule is this: pain that responds to over-the-counter medication and only appears with a trigger can usually wait a few days for a regular appointment. Pain that is constant, spontaneous, or accompanied by swelling or fever cannot.