A tooth infection typically announces itself with persistent, throbbing pain that doesn’t fade on its own, often accompanied by swelling in the gum, sensitivity to hot or cold that lingers well after the trigger is gone, and sometimes a foul taste in your mouth. These signs distinguish an active infection from ordinary tooth sensitivity, which produces brief discomfort that disappears within seconds once you stop eating or drinking something hot or cold.
How Pain Behavior Reveals the Problem
The single most telling clue is what your pain does after the thing causing it goes away. If you sip cold water and feel a sharp zing that vanishes within a few seconds, your tooth’s nerve is likely irritated but still healthy. Dentists call this reversible pulpitis, and it usually resolves with a filling or other minor treatment.
Once the pain starts lingering for a minute or more after the stimulus is removed, or starts showing up on its own with no trigger at all, the infection has likely reached the inner pulp of the tooth. At this stage the damage to the nerve is no longer reversible. The pain often shifts from sharp and intermittent to a deep, constant throb that can wake you up at night. You may also notice that biting down or pressing on the tooth intensifies it, because the pressure pushes against inflamed tissue or a pocket of pus at the root.
Visible Signs in Your Mouth
Look in the mirror with good lighting. A tooth infection often produces visible changes in the gum tissue around the affected tooth:
- Gum boil (parulis): A small, pus-filled bump on the gum, usually near the root of the tooth. It looks like a pimple and may occasionally burst on its own, releasing a salty or bitter-tasting fluid. This is actually a drainage channel the infection has created through the bone and gum tissue. The pain sometimes decreases when it drains, which can trick you into thinking the problem is resolving. It isn’t.
- Red, swollen gum tissue: The gum around the tooth may appear puffy, darker red than surrounding tissue, or tender to the touch.
- A tooth that looks darker: An infected tooth can gradually darken compared to its neighbors because the nerve tissue inside is dying.
If the infection originates in the gum pocket around the tooth rather than inside the tooth itself, you may notice the tooth feels slightly loose or seems to sit higher than usual when you bite down. This type of infection, called a periodontal abscess, develops in the space between the tooth and gum, often due to advanced gum disease or something like a piece of dental floss or food wedged deep under the gumline.
Where the Pain Spreads
Tooth infections rarely keep their pain neatly contained. The nerves supplying your teeth share pathways with nerves in your ear, jaw, and sinuses, so the pain frequently radiates outward. An infected upper molar can produce what feels like sinus pressure or a headache behind your cheekbone. Lower tooth infections commonly send pain along the jawline and into the ear, which is why some people visit their doctor for an “ear infection” that turns out to be dental.
This referred pain can make it hard to pinpoint exactly which tooth is the problem. You might feel like the whole side of your face aches. A dentist can narrow it down by tapping on individual teeth with an instrument handle and testing each one’s response to temperature changes.
Signs the Infection Is Spreading
A tooth infection that stays localized is painful but manageable with prompt dental treatment. The situation becomes dangerous when bacteria move beyond the tooth and surrounding bone into deeper tissues. Watch for these warning signs that the infection is no longer contained:
- Fever: Your body is now fighting the infection systemically.
- Facial swelling: Swelling that extends into the cheek, under the jaw, or down the neck means the infection is spreading through tissue spaces.
- Swollen lymph nodes: Tender lumps under your jaw or along the side of your neck indicate your immune system is mobilizing against a spreading infection.
- Difficulty swallowing or opening your mouth: This suggests the infection has reached the floor of your mouth or the muscles that control jaw movement.
These symptoms can escalate quickly. An infection that spreads into the floor of the mouth can cause the tongue to swell upward and forward, progressively blocking the airway. This condition, called Ludwig’s angina, is a medical emergency. Red flags include a “hot potato” voice (sounding like you’re talking around something in your mouth), drooling because you can’t swallow your own saliva, and leaning forward to breathe more easily. If you develop facial swelling with fever and can’t reach a dentist, go to an emergency room.
What Happens at the Dentist
A dentist confirms a tooth infection through a combination of simple tests. The percussion test involves tapping on the chewing surface and sides of the suspect tooth and its neighbors to reproduce your biting pain. Thermal testing uses cold (and sometimes heat) applied to the tooth while it’s isolated with a rubber shield. The dentist is watching whether you feel the temperature change at all and, critically, how long the sensation lasts after the stimulus is removed. A tooth with a healthy nerve responds briefly. A tooth with irreversible damage produces lingering pain. A completely dead nerve produces no response at all.
X-rays reveal what’s happening beneath the surface. A dark shadow at the tip of the root indicates a pocket of infection in the bone. The images also show the extent of any decay, cracks, or bone loss contributing to the problem, and help the dentist determine whether the tooth can be saved with a root canal or needs extraction.
Why It Won’t Resolve on Its Own
Unlike an infected cut on your skin, a tooth infection has no blood supply to deliver immune cells directly to the site once the nerve tissue dies. Antibiotics can control the spread temporarily, but they can’t eliminate an infection sealed inside a dead tooth or a deep gum pocket. The source has to be physically removed, either by draining the abscess, performing a root canal, or extracting the tooth.
Left untreated, the infection follows the path of least resistance through bone and soft tissue. A mild gum infection around a partially erupted wisdom tooth can progress into an abscess that expands into the spaces under the jaw and tongue, then down into the neck. In rare but documented cases, the bacteria enter the bloodstream and trigger sepsis, a body-wide inflammatory response that can cause organ failure. Deaths from dental infections are uncommon in countries with accessible dental care, but they still occur, almost always in cases where treatment was significantly delayed.
Infection vs. Other Causes of Tooth Pain
Not every toothache means infection. A cracked tooth can produce sharp pain on biting without any bacterial involvement. Grinding your teeth at night can leave your jaw and teeth aching in the morning. Gum recession exposes sensitive root surfaces that sting with cold drinks but don’t indicate infection. Sinus congestion can press on upper tooth roots and mimic a toothache on multiple teeth simultaneously.
The combination that most reliably points to infection is spontaneous throbbing pain (not triggered by eating or drinking), swelling or a gum boil, and pain that lingers long after any stimulus. If you have two or three of those together, you’re almost certainly dealing with an infection rather than simple sensitivity.