Pericoronitis shows up as red, swollen gum tissue partially covering a tooth that hasn’t fully come through, almost always a lower wisdom tooth. The inflamed area typically looks like a puffy flap of gum draped over the biting surface of the tooth, and it can range from mildly pink and tender to an angry, deep red with visible pus seeping from underneath.
The Gum Flap That Causes It
The hallmark visual feature of pericoronitis is a structure called the operculum: a flap of gum tissue that sits over a partially erupted tooth. When a wisdom tooth only breaks partway through the gumline, this flap creates a pocket between the gum and the tooth surface. Food particles, plaque, and bacteria collect in that pocket because it’s nearly impossible to clean with a toothbrush or floss. The trapped debris triggers inflammation, and that’s when the flap becomes visibly swollen, tender, and discolored.
In its earliest stage, you might notice the gum around your back molar looks slightly puffier than usual, with a reddish tint compared to the healthy pink tissue nearby. As the condition progresses, the flap itself becomes engorged enough that you can feel it with your tongue, and it may swell to the point where you accidentally bite down on it while chewing, which makes the irritation worse.
What Mild Pericoronitis Looks Like
Not every case of pericoronitis involves infection. In its inflammatory (non-infected) form, you’ll see localized swelling and redness around the gum flap, but no pus. The tissue looks irritated rather than infected. The gum may appear slightly raised or rounded compared to the flat, firm tissue on the opposite side of your mouth. Pain at this stage tends to be mild and localized right around the partially erupted tooth.
Chronic pericoronitis can look even more subtle. The gum flap stays slightly inflamed for weeks or months, flaring up occasionally. You might not see dramatic swelling, but the area stays a deeper shade of pink or red than the surrounding tissue. The most noticeable signs are often a persistent bad taste in your mouth and bad breath that doesn’t go away with brushing, both caused by bacteria thriving beneath the flap.
Signs of an Infected Flare-Up
Acute pericoronitis is more visually obvious and harder to ignore. The gum tissue becomes intensely red or even purplish, swells significantly, and may ooze pus or whitish-yellow drainage from beneath the flap. Pressing on the area or pulling the lip back to look at it can produce a visible discharge. The swelling can extend beyond the immediate tooth area, puffing up the surrounding gum tissue and the inside of the cheek.
At this stage, you’ll likely notice several things at once: the bad taste in your mouth becomes more pronounced (metallic or sour), chewing on that side becomes painful or impossible, and you may have difficulty fully opening your mouth. That limited jaw opening happens because the swelling and inflammation affect the muscles and tissues involved in jaw movement. Some people also develop a low-grade fever and notice swollen, tender lymph nodes under the jaw on the affected side, which can make the lower face look slightly asymmetric.
How It Differs From a Dental Abscess
A dental abscess and pericoronitis can look similar since both involve swelling and redness near a tooth, but the location and shape of the swelling are different. Pericoronitis centers specifically on the gum flap over a partially erupted tooth. The swelling hugs the crown of the tooth and you can often see or feel the flap itself. A dental abscess, by contrast, typically forms a distinct, rounded bump (like a pimple) on the gum, often near the root of a fully erupted tooth, and tends to have a more defined pocket of pus.
When pericoronitis progresses to an abscess stage (sometimes called a pericoronal abscess), the distinction blurs. At that point, pus accumulates more aggressively, the pain intensifies, and there’s a higher risk of the infection spreading to nearby tissue. If swelling extends noticeably into your cheek, jaw, or neck, the infection has moved beyond the localized gum flap and needs prompt treatment.
Which Teeth Are Affected
Pericoronitis occurs almost exclusively around lower wisdom teeth (the third molars at the very back of your mouth). These are the last teeth to come in, typically between ages 17 and 25, and they’re the most likely to erupt only partially because there isn’t enough room in the jaw. The combination of a partially erupted tooth and a gum flap creates the exact conditions bacteria need to thrive.
Recurrent pericoronitis is diagnosed when two or more distinct episodes affect the same partially erupted tooth within 12 months. Dentists evaluate the position and angle of the wisdom tooth using a panoramic X-ray to determine whether the tooth is likely to fully erupt on its own or whether extraction is the better option. In many cases, repeated flare-ups around the same tooth point toward extraction as the most effective long-term solution, since the gum flap won’t resolve as long as the tooth stays partially covered.
What to Look For in a Mirror
If you suspect pericoronitis, pull your cheek back and look at the gum tissue behind your last molar. Here’s what to compare against healthy tissue:
- Color: Healthy gums are pale pink and firm. Pericoronitis turns the tissue red, dark pink, or purplish.
- Shape: You’ll see a raised, rounded flap of tissue partially covering the tooth surface, rather than the gum sitting flat and tight against the tooth.
- Discharge: Gently pressing on the swollen area may produce whitish or yellowish pus. Healthy gums produce no discharge.
- Swelling extent: In mild cases, only the tissue immediately around the tooth is puffy. In more severe cases, the swelling spreads to the inner cheek or the gum tissue around neighboring teeth.
The visual signs alone can vary in intensity from day to day, especially with chronic pericoronitis. A flare-up might look alarming one morning and seem to improve by evening, only to return. That cycle of improvement and worsening is characteristic of the condition and doesn’t mean the underlying problem has resolved. As long as the gum flap remains over a partially erupted tooth, the conditions for another episode are still in place.