Gum boil (parulis): what it is and why it needs treatment

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A small, pus-filled bump appearing on your gum, often painless at first, is easy to dismiss or mistake for an ulcer. It is actually one of the clearer signs the body gives that a tooth underneath is infected, and it is worth taking seriously even when it does not hurt.

Why a gum boil forms

When the nerve inside a tooth dies, usually from deep decay that was never treated, a crack that let bacteria in, or a previous root canal that did not fully resolve, infection builds at the root tip inside the jawbone. Pressure from this infection eventually finds the path of least resistance, tracking up through the bone and gum to form a small opening, the boil, where pus can drain. The boil may come and go as pressure builds and releases, which misleads some people into thinking the problem has resolved. It has not. Our guide to dental abscess warning signs covers the related, more acute presentation of the same underlying problem.

Gum boil vs mouth ulcer: telling them apart

An ulcer is shallow, round, usually pale or white-centred with a red border, typically on the inside of the cheek, lip or tongue rather than directly on the gum near a tooth, and painful to touch. A gum boil is firmer, raised, specifically on the gum near a tooth root, often less painful than you would expect given what is happening underneath, and does not heal within the one to two weeks a normal ulcer would. If you are unsure, the location (directly over a tooth root versus on soft cheek or lip tissue) is usually the clearest clue, and our guide to mouth ulcers explains the three-week warning sign for anything that is genuinely an ulcer but will not heal.

Why popping it does not help

The visible bump is just the drainage point; the actual infection sits inside the bone at the tooth root, out of reach of anything you can do at home. Popping it may release some pressure temporarily, but the infection refills the space within days. Squeezing also risks pushing bacteria into surrounding soft tissue rather than letting it drain safely.

Treating the actual cause

An X-ray typically shows a dark area at the root confirming infection in the bone. If the tooth structure allows it, root canal treatment removes the infected nerve tissue, and the boil usually resolves within a week or two as healing begins. If the tooth is too damaged or infected to save, extraction removes the source instead. Antibiotics can be prescribed for an acute flare-up but are not a standalone cure; our guide on whether antibiotics cure a tooth infection explains why the dead nerve tissue has to be physically addressed.

Sources & further reading

American Dental Association (MouthHealthy) · NHS, Dental Health · NIDCR, US National Institute of Dental & Craniofacial Research · Indian Dental Association