An infected tooth often looks noticeably different from the healthy teeth around it. The tooth itself may turn dark gray, brown, or black, and the gum tissue nearby can become red, swollen, or develop a small pus-filled bump. The specific signs depend on how far the infection has progressed, from early discoloration all the way to visible facial swelling.
Color Changes in the Tooth
One of the earliest visible signs of a tooth infection is a change in color. A healthy tooth has a consistent white or off-white shade, but an infected tooth can darken to gray, brown, or even black. This darkening happens because the nerve and blood supply inside the tooth are dying or already dead. In a study tracking discolored teeth over time, 83% of teeth that developed clinical signs of infection had turned dark (black, gray, or brown) rather than yellow. A tooth that shifts to a darker hue, especially without any obvious cause like coffee staining, is a strong visual clue that something is wrong internally.
Not every discolored tooth is infected, but the pattern matters. A single tooth that looks noticeably darker than its neighbors is far more suspicious than generalized yellowing across several teeth. If the darkening appeared after trauma or gradually worsened over months, infection of the inner pulp tissue is a likely cause.
Visible Decay and Structural Damage
Many tooth infections start with untreated cavities, so you may see obvious holes, pits, or crumbling edges on the tooth surface. In early stages, decay can look like a white chalky spot or a light brown area. As it deepens, the cavity turns darker brown or black and becomes a visible hole. By the time bacteria reach the inner pulp chamber and cause infection, the decay is usually extensive enough to see with the naked eye or feel with your tongue.
In some cases, a large portion of the tooth’s crown breaks away, leaving behind a jagged stump. You might also notice that the edges of the tooth feel sharp or rough. Food getting trapped in a visible cavity and causing a bad taste is another common observation people report before learning the tooth is infected.
Gum Changes Around the Tooth
The gum tissue surrounding an infected tooth often tells the story just as clearly as the tooth itself. Look for these changes:
- Redness and swelling: The gum around the affected tooth appears puffy and darker red compared to the pink tissue elsewhere in your mouth.
- Gum boil (parulis): A small, round bump on the gum near the tooth, usually white or yellowish at the center. This is a drainage point where pus from a deep abscess finds its way to the surface. It may come and go, sometimes bursting and leaving a salty or foul taste in your mouth.
- Receding or pulling-away gum: The gum line around the tooth may look lower than usual, exposing more of the tooth root.
- Pus between the tooth and gum: Pressing gently on the swollen gum may produce a small amount of yellowish or whitish discharge.
A gum boil is one of the most distinctive visual signs of a tooth infection. It forms when an abscess at the tip of the tooth root creates a tunnel (called a fistula) through the jawbone and gum tissue, allowing pus to drain into the mouth. The bump typically sits on the gum right below or above the infected tooth.
Swelling Beyond the Gums
When infection spreads past the tooth and surrounding gum into deeper tissues, visible swelling can appear on the face, jaw, or neck. An infected upper tooth may cause swelling in the cheek or below the eye. An infected lower tooth often produces swelling along the jawline or under the chin. The overlying skin can look slightly red or feel warm and tight to the touch. Clinical descriptions of dental cellulitis note diffuse cheek swelling with slight redness as a characteristic presentation.
This type of swelling is firm rather than soft and doesn’t move around when you press on it. It’s distinctly different from the puffiness of an allergic reaction, which tends to affect both sides of the face. One-sided facial swelling that developed gradually over hours or days, especially alongside a toothache, strongly suggests a spreading dental infection.
What Shows Up on an X-Ray
Some of the most important signs of a tooth infection aren’t visible to the naked eye at all. On a dental X-ray, an infected tooth typically shows a dark shadow at the tip of the root, representing an area where bone has been destroyed by the infection. A periapical abscess appears as an irregular dark area at the root tip, while a more chronic infection (granuloma) shows a well-defined round dark spot, usually smaller than 1.6 centimeters. The thin white line that normally outlines a healthy tooth root on X-ray disappears partially or completely around an infected tooth.
This is why a tooth can sometimes look relatively normal on the surface while harboring a significant infection underneath. Your dentist may take an X-ray of a tooth that appears only slightly discolored and discover a large abscess at the root that has been silently eroding bone.
Signs That Need Urgent Attention
Certain visible changes indicate a dental infection is becoming dangerous. Dental professionals use a set of red-flag features to identify infections that may need hospital-level care:
- Swelling around the eye: Puffiness or redness near the eye socket can signal that infection from an upper tooth is spreading toward the orbit.
- Inability to open your mouth: If you can’t open wider than about 3 centimeters (roughly two finger-widths), infection may have reached the muscles controlling your jaw.
- Swelling in the floor of the mouth: A raised, firm area under the tongue or a tongue that can’t move freely suggests infection is spreading into the airway region.
- Neck swelling or stiffness: Painful neck movements or visible swelling in the neck points to deep tissue involvement.
- Difficulty swallowing or drooling: This suggests swelling near the throat and potential airway compromise.
- Fever above 38°C (100.4°F) or feeling cold and clammy: A systemic response like this, combined with a rapid heart rate, signals the body is fighting a serious infection.
Any combination of these visible and physical signs alongside a known bad tooth warrants immediate care, not a wait-and-see approach. A dental infection that spreads to the neck or airway can become life-threatening within hours.
How Infected Teeth Look at Different Stages
In the earliest stage, an infected tooth may look almost normal, with just a small cavity or slight graying. You might not notice anything unusual by looking in the mirror. Pain or sensitivity to hot and cold drinks may be the only clue.
As the infection progresses, the tooth darkens further, the cavity enlarges, and gum swelling becomes noticeable. A dull, throbbing ache replaces the sharp sensitivity. At this point, the tooth might look obviously damaged, and the surrounding gum tissue is visibly red or puffy.
In advanced stages, you may see a gum boil draining pus, significant facial swelling on one side, or a tooth so broken down it’s barely recognizable. The gum tissue may bleed easily or appear almost purple from inflammation. At this point, the infection has typically been present for weeks or months, even if the pain has come and gone. Teeth that remain dark gray or black over time are far more likely to develop complications like root resorption, where the body begins breaking down the tooth root itself.