An infected tooth can look surprisingly normal from the outside, especially in the early stages. The most visible signs tend to appear on the gum tissue around the tooth rather than on the tooth itself. As an infection progresses, you may notice gum swelling, a pimple-like bump near the tooth’s root, discoloration of the tooth, or facial swelling along the jaw and cheek.
The Tooth Itself May Change Color
When infection reaches the inner pulp of a tooth and kills the nerve, the tooth loses its blood supply. Without blood flow, the tooth changes color in a predictable sequence: it starts turning yellow, shifts to gray, and eventually darkens to black. This discoloration happens gradually, sometimes over weeks or months, and it affects the entire tooth rather than just one spot. A single dark or gray tooth surrounded by normal-looking neighbors is a classic sign of a dead nerve, which often means infection is present or developing.
Not every infected tooth changes color, though. If the infection originates from gum disease rather than from inside the tooth, the tooth itself may look perfectly fine while the surrounding tissue tells a different story.
What the Gums Look Like Around an Infected Tooth
The gums are where most visible signs of infection show up. Depending on the type and severity, you might see several things.
A gum boil (dentists call it a parulis) is the most recognizable sign. It looks like a small, smooth, raised bump on the gum near the base of a tooth. It can be yellow, red, or pink, and it’s soft or squishy to the touch. This bump is actually the exit point of a drainage tunnel that runs from the infection at the tooth’s root up through the bone and gum tissue. If you press on it lightly, pus may ooze out. Some people mistake it for a canker sore, but a gum boil sits right next to the problem tooth and tends to come and go as the infection flares up and partially drains.
Swelling along the gumline is another common sign. The gum tissue near the infected tooth may look puffy, dark red, or shiny. With a periodontal abscess (an infection originating from the gum), you’ll typically see swelling right at the gumline. With a periapical abscess (an infection starting inside the tooth), the swelling often appears higher up on the gum, closer to where the root tip sits beneath the surface. Both types can drain pus onto the gum surface.
What You Feel but Can’t Always See
Early-stage infection inside a tooth often has no visible signs at all. The earliest phase, called reversible pulpitis, causes sharp sensitivity to cold or sweets that disappears quickly. The tooth looks completely normal. There’s no swelling, no discoloration, and no bump on the gum.
As the infection advances to an irreversible stage, you’ll notice sensitivity that lingers for more than a few seconds after the trigger is gone. Pain shifts from sharp to a deep, throbbing ache. The tooth may feel tender when you bite down or tap on it. Even at this stage, the tooth can still look visually unchanged.
Once the nerve tissue dies completely, an odd thing happens: the sensitivity to hot and cold disappears. Some people interpret this as the problem resolving. It hasn’t. The infection is still active and spreading into the bone. The tooth may still hurt when pressure is applied to it, and eventually the visible signs described above will develop.
Swelling That Spreads Beyond the Mouth
When a tooth infection isn’t treated, it can push beyond the gums and into the soft tissues of the face. This is when the infection becomes visible to everyone around you, not just when you open your mouth.
Facial swelling from a dental infection typically appears on the cheek or along the jawline on the same side as the infected tooth. The skin may look tight, flushed, or warm to the touch. You might also notice tender, swollen lumps under your jaw or along your neck. These are lymph nodes reacting to the infection.
The location of facial swelling depends on which tooth is infected. Lower back teeth tend to cause swelling along the jawline and into the neck. Upper teeth can cause swelling in the cheek, under the eye, or along the side of the nose.
What an Infected Tooth Looks Like on an X-Ray
Because so much of a tooth infection happens beneath the surface, X-rays reveal what your eyes can’t. On a dental X-ray, infection at the root tip appears as a dark circle or shadow at the bottom of the tooth. This dark area represents bone that has been destroyed by the infection and replaced with inflamed tissue or pus. Healthy bone appears bright white on X-rays, so the dark spot stands out clearly.
The X-ray also usually shows what caused the infection in the first place. A large cavity, a deep filling, or a fracture line in the tooth will be visible alongside the dark area at the root. The larger and more well-defined the dark circle, the more established the infection. Dentists rely heavily on X-rays because a tooth can have significant infection at its root while still looking relatively normal in your mouth.
Signs That Need Emergency Attention
Most tooth infections develop slowly, but some progress into dangerous territory. A condition called Ludwig’s angina occurs when infection from a lower tooth spreads into the floor of the mouth and the neck. The visual signs are dramatic: the area under the jaw and the front of the neck become visibly swollen and may look discolored. The tongue can push forward or swell, and the floor of the mouth feels firm and board-like rather than soft.
Difficulty breathing, difficulty swallowing, drooling, fever with chills, or rapidly worsening swelling that spreads from the jaw into the neck are all signals of a spreading infection that requires emergency care. Swelling that moves toward the throat or makes it hard to open your mouth is particularly concerning, as it can compromise your airway.