A toothache almost always means something is irritating the nerve inside or around your tooth. Teeth contain a soft core called the pulp, packed with nerve fibers and blood vessels. When decay, a crack, or inflammation reaches that core, or even gets close to it, those nerves fire pain signals through the trigeminal nerve to your brain. The specific pattern of your pain, whether it’s sharp, dull, constant, or triggered by hot and cold, points toward different causes.
How Teeth Feel Pain
Your teeth aren’t solid blocks of bone. Beneath the hard outer enamel sits a layer called dentin, which is softer and riddled with microscopic tubes. Those tubes connect to nerve endings deep inside the pulp. When something breaches the enamel or exposes the dentin, fluid inside those tiny tubes shifts in response to temperature, pressure, or sugar. That fluid movement activates nerve fibers, producing that sharp, unmistakable zing.
This is why a tooth can hurt from ice cream, hot coffee, or a bite of candy even when there’s no visible damage. The nerve fibers running through each tooth exit through a small opening at the root tip, joining a larger nerve network that carries signals to your brain. Once those signals fire, the pain can feel enormous relative to the size of the problem, because teeth are densely wired with sensory neurons.
Cavities: The Most Common Cause
Nearly 21% of U.S. adults between 20 and 64 have at least one untreated cavity, making decay the single most likely reason your tooth hurts. Cavities progress in stages, and the pain changes with each one.
In the earliest stage, bacteria produce acid that eats through your enamel, creating tiny holes. You probably won’t feel anything yet. Once the decay reaches the dentin layer underneath, you’ll start noticing sensitivity to sweets, cold drinks, or hot food. Dentin is softer and less resistant to acid, so decay accelerates here.
If the cavity keeps growing, bacteria eventually reach the pulp. Because the pulp sits inside a rigid shell of tooth, any swelling has nowhere to expand. The nerve gets compressed, producing intense, throbbing pain that can wake you up at night. At this point, the problem won’t resolve on its own.
Reversible vs. Irreversible Damage
One of the most useful things you can figure out is whether your pain stops quickly or lingers. This distinction changes what treatment looks like.
If you feel a sharp pain when something cold or sweet touches the tooth, and it disappears within one to two seconds after you remove the trigger, the pulp is likely inflamed but still healthy. This is called reversible pulpitis. A filling is usually enough to fix it.
If the pain sticks around for minutes after the trigger is gone, or shows up on its own without any trigger at all, the pulp is dying or already dead. Heat tends to be the main provocateur at this stage rather than cold. This situation typically requires a root canal or extraction, because the tissue inside the tooth can no longer recover.
A tooth that has gone completely numb after weeks of pain isn’t necessarily better. It may mean the nerve has died. You might still feel pain when tapping on the tooth or biting down, because infection can spread beyond the root tip into the surrounding bone.
Cracked Teeth
A cracked tooth produces a distinctive pain pattern: a sharp jolt when you bite down, followed by pain when you release the bite. You might notice it only with certain foods or when chewing on one side. The crack may be invisible to the naked eye and even hard to spot on an X-ray.
Cracks let bacteria seep into the interior of the tooth and allow fluid movement in the dentin that triggers nerve endings. Temperature sensitivity and pain with sweet foods are common. Dentists often diagnose cracks by having you bite on a small stick tooth by tooth to isolate which one reproduces the pain.
Exposed Roots and Sensitivity
If your pain is a short, sharp sting triggered by cold air, cold water, or brushing, you may have dentin hypersensitivity from exposed tooth roots. This happens when gums recede and pull away from the tooth, uncovering root surfaces that lack enamel’s protection.
The exposed dentin has open tubules that respond to temperature changes, touch, and even airflow across the tooth surface. Aggressive brushing, acidic foods, and gum disease all contribute to recession. Unlike a cavity, there’s no hole forming. The pain comes purely from the nerve-rich dentin being in direct contact with your environment. Desensitizing toothpastes work by gradually blocking those open tubules, reducing fluid movement and calming the nerve response over several weeks of use.
Tooth Abscess
An abscess forms when infection from a dead or dying tooth spreads beyond the root tip into the jawbone and surrounding tissue. The pain is typically constant, throbbing, and can radiate into your jaw, ear, or neck. You might notice a swollen bump on your gum near the affected tooth, a bad taste in your mouth, or swollen lymph nodes under your jaw.
Most abscesses need professional drainage and antibiotics. If you develop a fever along with facial swelling, or if you have difficulty breathing or swallowing, that signals the infection may be spreading into deeper tissues of the jaw, throat, or neck. This is a genuine emergency that warrants an ER visit if you can’t reach a dentist.
Sinus Pressure Mimicking a Toothache
Not every toothache starts in a tooth. Your largest sinuses sit directly above the roots of your upper back teeth. In some people, the roots actually extend into the sinus cavity. When those sinuses become inflamed from a cold, allergies, or a sinus infection, the pressure can produce aching pain in your upper molars that feels exactly like a dental problem.
The giveaway is that sinus-related tooth pain usually affects multiple upper teeth at once rather than a single tooth, and it often comes with nasal congestion, facial pressure, or a runny nose. If the pain shifts when you bend forward or worsens with head position changes, your sinuses are the more likely culprit.
Grinding and Clenching
If your teeth hurt when you wake up, or you notice jaw stiffness, soreness at your temples, or pain that feels like an earache, you may be grinding your teeth at night. This habit puts enormous repetitive force on your teeth and jaw joints, leading to generalized tooth sensitivity, worn-down enamel, and sometimes cracked teeth.
Grinding pain tends to be diffuse rather than localized to one tooth. You might also notice a tired or tight jaw, neck soreness, or a dull headache concentrated at the temples. Many people grind without knowing it until a dentist spots the wear patterns or a partner hears the sound. A custom night guard reduces the force on your teeth and often resolves the morning pain within days.
Why Tooth Pain Often Gets Worse at Night
If your toothache seems tolerable during the day but unbearable at bedtime, you’re not imagining it. Lying down increases blood flow to your head, which raises pressure inside the already-inflamed pulp tissue. Since the pulp is trapped inside a rigid tooth, even a small increase in blood pressure amplifies the compression on the nerve. Propping your head up with an extra pillow can take the edge off until you can get treatment.
Nighttime also removes distractions. During the day, activity and stimulation compete for your brain’s attention. In a quiet, dark room, the pain signal has less competition, making it feel more intense.