How to Spot an Infected Baby Tooth

The Signs You Can See or Notice at Home

The most common early signs of an infected baby tooth are a toothache that's worse with chewing, pressure, or hot and cold; visible swelling or redness in the gum around one specific tooth; and a small, pimple-like bump on the gum, sometimes called a gum boil, that may come and go. A child may also avoid chewing on one side of the mouth, refuse foods that were fine a week earlier, or wake at night from tooth pain that a dose of over-the-counter pain reliever only partly touches.

A bump on the gum that keeps coming back is one of the more reliable signs something is wrong, even without pain, since some infected baby teeth don't hurt constantly — nerve tissue in a primary tooth can die quietly, without the ongoing ache an adult might expect from an infected tooth.

How a Cavity Turns Into an Infection

Tooth decay starts when bacteria on the tooth surface feed on sugars and produce acid that wears away enamel, and left untreated, that process doesn't stop at the enamel — it continues inward through the dentin toward the pulp, the living tissue at the center of the tooth that holds its nerve and blood supply 1Ref 1National Institute of Dental and Craniofacial Research (2024).Tooth Decay.Decay develops when bacteria convert dietary sugars to acids that demineralize enamel and progress inward toward the pulp. Decay is the most common chronic disease of childhood, which is part of why an infected baby tooth is a routine finding in a pediatric dental office rather than a rare one 2Ref 2Centers for Disease Control and Prevention (2024).Untreated Cavities in Children.About 11% of children aged 2-5 have at least one primary tooth with untreated decay, making an infected baby tooth a routine finding.

Once bacteria reach the pulp, the tissue can become inflamed and eventually die, and a dead or dying pulp is an environment bacteria can multiply in without the usual blood-supply defenses reaching it. From there, the infection can spread past the root tip into the surrounding bone and gum — which is when an abscess, and the parulis that sometimes accompanies it, forms 3Ref 3American Dental Association (2024).Abscess.A dental abscess is an infection caused by tooth decay that allows bacteria into the pulp, which can lead to pulp death.

This is why an infected baby tooth can look, from a parent's side, like it came out of nowhere: the visible cavity that started the process may have been small or even unnoticed, since decay doesn't need to look dramatic on the outside to be doing serious damage on the inside.

Facial Swelling and Fever

When an infection spreads beyond the tooth itself into the surrounding tissue, the picture changes from a localized ache or gum bump to something more visible: swelling in the cheek or jaw, a face that looks asymmetric compared to normal, or a fever that wasn't there a day before. This represents the infection moving into soft tissue rather than staying contained near the tooth root, and it's a different situation from a bump that drains and settles back down on its own.

The safety box below covers exactly which combination of swelling, fever, and other signs means same-day or emergency care rather than a routine dental appointment — the short version is that swelling reaching toward the eye or under the jaw, especially paired with fever, is the pattern that changes the timeline.

How Dentists Treat an Infected Baby Tooth

Treatment depends on how much of the tooth's pulp is affected and how much healthy tooth structure remains. If only the crown portion of the pulp is involved, a dentist may be able to perform a pulpotomy — removing the affected pulp tissue, treating the area, and sealing and typically crowning the tooth to preserve it, similar in concept to how an infected pulp is addressed in adult teeth through root canal treatment, though the specific technique in a primary tooth differs 4Ref 4American Association of Endodontists (2024).Root Canal Treatment.Removing inflamed or infected pulp tissue and sealing the tooth is the general concept behind treating an infected tooth, as applied in root canal treatment.

When the infection has progressed too far to save the tooth, or the tooth is close enough to its natural exfoliation date that saving it doesn't add much, extraction may be the more practical option, sometimes followed by a space maintainer to hold room for the permanent tooth coming in behind it.

Either way, the goal at this stage shifts from preventing an infection to stopping the one that's already there and protecting the space it occupies, since a baby tooth lost early to infection can still affect how the permanent tooth behind it comes in.

The Gum Boil That Keeps Coming Back

A gum boil that keeps coming back is usually the drainage point for what's called a chronic dental sinus tract — a channel the infection has formed from the tooth root to the surface of the gum, which lets pressure release periodically rather than building up into a painful, swollen abscess. The bump may shrink or disappear between flare-ups, which can make it look like the problem resolved on its own, but the underlying infected tooth is still there and the tract will keep reopening until the source is treated.

This pattern is worth mentioning to a dentist even if the bump isn't currently painful or swollen, since a parent's description of a spot that comes and goes over weeks or months is often the detail that points a dentist toward the right tooth on an exam.

Keeping New Infections From Starting

Regular dental visits, recommended starting at a child's first tooth and no later than their first birthday, are what catch decay while it's still a small, treatable spot rather than an infection reaching the pulp 5Ref 5American Academy of Pediatric Dentistry (2023).Periodicity of Examination, Preventive Dental Services, Anticipatory Guidance/Counseling, and Oral Treatment for Infants, Children, and Adolescents.Recommends a child's first dental visit at eruption of the first tooth and no later than 12 months of age. A checkup schedule kept on track, rather than visits driven only by a complaint of pain, is the most reliable way to avoid getting to the abscess stage at all.

Early childhood tooth decay from prolonged bottle or sippy-cup use at night is one of the more common paths to an infected baby tooth in very young children, since sugars sitting on teeth for hours overnight give bacteria an extended window to work. Baby bottle tooth decay covers how that pattern develops and how it's prevented.