The most reliable sign of a tooth infection is persistent, throbbing pain that intensifies when you bite down, chew, or lie flat. Unlike a standard toothache from sensitivity or a crack, an infected tooth produces pain that doesn’t fade on its own and often worsens over days. If swelling, fever, or a foul taste accompany that pain, infection is very likely.
Pain That Points to Infection
Tooth infections cause a distinctive kind of pain. As bacteria multiply inside the tooth or in the surrounding gum tissue, pus builds up in a confined space, pressing against the inner walls of the tooth or bone. That pressure creates severe, often throbbing pain that can radiate into your jaw, ear, or neck on the same side. It’s typically worse when you press on the tooth, tap it, or chew with it.
What separates infection pain from ordinary sensitivity is persistence and escalation. A sensitive tooth might sting briefly when you drink something cold. An infected tooth hurts steadily, and the pain tends to get worse over hours or days rather than resolving. Many people notice it intensifies at night or when they bend forward, because changes in blood flow increase pressure at the infection site. If over-the-counter pain relievers barely take the edge off, that’s another signal something deeper is going on.
Visible Signs Inside Your Mouth
You can sometimes spot a tooth infection just by looking. The gum around the affected tooth may appear red, swollen, or puffy compared to the tissue around neighboring teeth. In some cases, you’ll see a small bump on the gum that looks like a pimple. This is a fistula, a channel the body creates to drain pus. It may come and go.
The tooth itself can also change. Infected teeth sometimes darken to a gray or yellowish color, which signals that the nerve inside has died. You might also notice visible damage: a deep cavity, a crack, or a broken filling that exposed the interior of the tooth to bacteria in the first place.
Taste, Smell, and Drainage
A sudden rush of foul-tasting, salty fluid in your mouth is a strong indicator. This happens when an abscess ruptures on its own, releasing pus. The taste is unmistakable: bitter, metallic, and unpleasant. You’ll likely notice immediate pain relief when this happens, because the pressure drops. But the infection is still there. The drainage may continue intermittently, and persistent bad breath that doesn’t improve with brushing often accompanies it.
Swelling Beyond the Tooth
Swelling is one of the clearest signs that a simple toothache has become an infection. It usually starts in the gum, then can spread to the cheek, jaw, or under the chin depending on which tooth is involved. Lower tooth infections tend to cause swelling along the jawline or under the tongue. Upper tooth infections can cause swelling near the eye or along the cheekbone.
If the swelling is firm, warm to the touch, and growing, the infection is actively spreading into surrounding tissue. Some people also develop swollen lymph nodes under the jaw or along the neck, which is the body’s immune response trying to contain the bacteria.
Two Types of Tooth Infections
Not all dental infections start the same way, and knowing the difference helps explain why symptoms can vary.
A periapical abscess starts inside the tooth. It follows a familiar path: a cavity or crack allows bacteria into the soft tissue (the pulp) at the tooth’s core, causing inflammation. Left untreated, the pulp dies. Dead tissue is highly vulnerable to infection, and bacteria eventually push through the root tip into the surrounding bone, forming an abscess. This type often causes sharp, localized pain and sensitivity to hot and cold that may disappear once the nerve dies, only to return as deeper, pressure-like pain when the abscess forms.
A periodontal abscess starts in the gum. It forms when a periodontal pocket, the small gap between tooth and gum, gets blocked by hardened plaque, a fragment of food, or even a piece of dental floss wedged into the tissue. Pus accumulates in the gum wall itself. This type tends to cause a visible swelling right next to the tooth, gum tenderness, and sometimes bleeding. Pain is usually less intense initially but can escalate quickly.
How Infections Progress
Tooth infections don’t develop overnight. The process typically starts with enamel damage from decay, wear, or trauma. Bacteria work through the enamel and the harder layer beneath it (dentin), eventually reaching the pulp. The pulp becomes inflamed, a condition called pulpitis. Early pulpitis can still be reversed with treatment. But once the inflammation kills the nerve, the tooth becomes a breeding ground for bacteria, and an abscess can form at the root tip.
The timeline varies. A small cavity can take months or even years to reach the pulp. But a cracked tooth or a deep cavity close to the nerve can progress to infection in weeks. Once an abscess forms, it won’t resolve without professional treatment. The body can’t clear the infection on its own because there’s no blood supply to deliver immune cells inside a dead tooth.
Signs the Infection Is Spreading
Most tooth infections stay localized, but some spread into surrounding tissues or the bloodstream. This is where the situation becomes genuinely dangerous. Watch for these warning signs:
- Fever: a temperature above 100.4°F (38°C) suggests your body is fighting a systemic infection, not just a local one.
- Difficulty swallowing or opening your mouth: this indicates the infection has spread into the muscles or tissue spaces of the throat and jaw.
- Swelling that spreads rapidly: particularly under the tongue, along the floor of the mouth, or down toward the neck.
- Feeling generally unwell: fatigue, chills, rapid heart rate, or confusion alongside dental pain.
When infection spreads into the deep tissue spaces under the jaw and tongue, it can compromise the airway. If it tracks downward into the chest cavity, a condition called descending necrotizing mediastinitis, mortality rates remain between 25 and 40% even with modern treatment. These outcomes are rare, but they underscore why a spreading dental infection isn’t something to wait out. Other documented complications include bone infection, infection spreading toward the brain, and sepsis.
What Happens at the Dentist
If you suspect an infection, a dentist can confirm it quickly. The exam usually involves tapping on the suspected tooth and the teeth around it, since an infected tooth is almost always sensitive to pressure. They’ll press on the gum tissue to check for swelling or tenderness and look for visible signs like discoloration, gum redness, or drainage.
Thermal testing, applying cold or heat to the tooth, checks whether the nerve is still alive. A tooth that doesn’t respond at all to temperature likely has a dead nerve, which supports an infection diagnosis. An X-ray can reveal a dark area at the root tip where bone has been destroyed by the abscess. This shadow, called a radiolucency, is one of the most definitive signs. In periodontal abscesses, the X-ray may show bone loss along the side of the root instead.
Treatment depends on the type and severity. The core goal is always the same: drain the infection and eliminate the source. For a periapical abscess, that typically means a root canal or extraction. For a periodontal abscess, it involves draining the pocket and cleaning out the debris that caused the blockage. Antibiotics alone won’t cure a tooth infection because the medication can’t penetrate effectively into dead tissue or walled-off pus. They’re used as a support tool when the infection has spread beyond the tooth itself.
Signs You Might Be Misreading
Not every toothache is an infection. A cracked tooth can cause sharp pain when you bite down without any bacteria being involved. Gum recession can expose root surfaces that react painfully to cold drinks. Sinus pressure from a cold or allergies can mimic upper tooth pain on both sides. Grinding your teeth at night can leave them sore and tender in the morning.
The combination of symptoms matters. Pain plus swelling, pain plus fever, pain plus a foul taste, or pain that steadily worsens over days all point more strongly toward infection than pain alone. A single symptom in isolation is harder to interpret, but a cluster of two or three from the signs described above makes infection the most likely explanation.