By Dr. Liyan Massaband, DMD, MPH · Last updated: 29 Sept 2026
Quick answer: The main signs of infection after a root canal are pain that gets worse instead of better, swelling that grows or comes back, a pimple or bump on the gum near the tooth, a bad taste or pus, tenderness when you bite that does not fade, and fever or feeling unwell. Mild soreness and slight swelling in the first few days are normal. What sets an infection apart is the direction: normal healing improves every day, and an infection stays the same, gets worse, or returns after you felt better. Some infections cause no symptoms at all and only show up on an X-ray.
Key takeaways
- Judge by the trend. Symptoms that improve each day are healing. Symptoms that stall, worsen or return are a warning sign.
- A gum bump that drains is the most reliable single sign of an ongoing infection.
- A root canal tooth should not react to hot and cold. If it does, something needs checking.
- Infection can appear weeks, months or years later, often under an old crown.
- Swelling near the eye or neck, trouble swallowing or breathing, or a high fever needs emergency care.
First, What Is Normal After a Root Canal?
Some discomfort is part of healing. According to the American Association of Endodontists, tenderness for a few days and a sore jaw from keeping your mouth open are common and usually respond to over-the-counter pain relief.
| Usually normal | Possible sign of infection |
| Tenderness when biting for a few days | Biting pain that is the same or worse after 1 to 2 weeks |
| Mild swelling that peaks around day 2 to 3, then shrinks | Swelling that keeps growing after day 3, or returns later |
| A dull ache controlled by ibuprofen | Throbbing pain that wakes you at night or needs more and more medicine |
| Slight gum soreness around the tooth | A gum bump, pus or a bad taste |
| Feeling a little tired on the day of treatment | Fever, chills or feeling unwell days later |
For a day-by-day guide to normal healing, see our article on swelling after a root canal.
9 Signs of Infection After a Root Canal
1. Pain that gets worse or comes back
Pain should ease steadily over the first week. Pain that builds after day 3, throbs, wakes you at night, or returns weeks after the tooth felt fine is one of the most common signs that bacteria are still active around the root.
2. Pain when you bite or tap on the tooth
Mild biting tenderness is normal for a short time. Tenderness that lasts beyond two weeks, or sharp pain when you bite down on one spot, can mean inflammation at the root tip, a high filling or a crack in the root.
3. Swelling that grows or returns
Swelling of the gum, cheek or jaw that keeps getting bigger after the first few days, or disappears and then comes back, suggests an active infection rather than normal healing.
4. A pimple, bump or boil on the gum
A small bump near the tooth, sometimes called a gum boil, fistula or sinus tract, is a drainage channel for pus. It may come and go, and it often does not hurt, because the pus has an escape route. If the bump was there before treatment, it may shrink and close over a few weeks. If it appears after treatment or keeps draining, the infection has not cleared. Learn why an abscess can persist after a root canal.
5. A bad taste, bad breath or pus
A salty, bitter or foul taste that keeps coming back, especially when you press near the tooth, usually means pus is draining into your mouth.
6. Red, puffy or tender gums around the tooth
Gums that stay swollen, red or sore around one tooth, or feel spongy when you press, can signal infection. Sometimes this is a gum problem rather than the root canal, which is covered below.
7. The tooth feels “high” or loose
Infection at the root tip causes swelling in the ligament that holds the tooth, which can push it up slightly. Your teeth may hit that tooth first when you close. A tooth that starts to feel loose is a later sign and should be seen promptly.
8. Sensitivity to hot or cold
Once the nerve is removed, a root canal tooth should not feel hot or cold. If you feel a sharp reaction to temperature, it can mean a canal still holds living nerve tissue, or that the pain is actually coming from a neighboring tooth. Either way, it is worth checking.
9. Fever, chills or feeling unwell
Fever, chills, unusual tiredness or tender swollen glands under the jaw suggest the infection is spreading beyond the tooth. Call your dentist the same day.
Sometimes there are no symptoms at all
Many infections on root canal teeth are painless, because the tooth no longer has a nerve to sound the alarm. These are found on follow-up X-rays as a dark area around the root tip that is not shrinking. This is why follow-up visits matter even when you feel fine.
Signs of Infection by Timeframe
In the first week
Most discomfort in the first week is healing. The warning signs are swelling that is still growing after day 3, pain that gets worse instead of better, fever, or swelling spreading toward the eye or neck.
Weeks to months later
A gum bump that appears or will not close, biting pain that never fully settled, or a bad taste suggests the first treatment did not fully clear the infection. Common reasons include a missed canal or a canal too curved or narrow to clean completely.
Years later
A root canal tooth can become infected long after it healed, usually because bacteria leaked back in through a worn filling, a gap under a crown, new decay or a crack. The signs are the same: tenderness, a gum bump, swelling or a bad taste in a tooth that had been comfortable for years.
Infection Under a Root Canal With a Crown: Symptoms and Causes
Because the crown covers the tooth, infection underneath is easy to miss. Watch for:
- Tenderness when biting on a crowned tooth that used to feel fine
- A gum bump or swelling near the crown
- Gum that looks dark, swollen or bleeds easily along the edge of the crown
- A bad taste around that tooth
- A crown that feels loose or has a visible gap
The usual causes are decay creeping under the crown’s edge, a crown that has come loose from its cement, or a crack in the root beneath it. If you have been living with a temporary filling instead of a permanent crown, the risk of reinfection is higher.
Gum Infection or Tooth Infection After a Root Canal?
Not every swelling near a root canal tooth comes from the root canal. A gum (periodontal) abscess starts in a deep pocket between the gum and tooth, often from gum disease or trapped food. A tooth infection starts inside the root and drains from the root tip. They can look almost identical, so your dentist measures the gum pockets and takes an X-ray to tell them apart. The treatment is different, so getting this right matters.
Upper Teeth: When an Infection Feels Like Sinusitis
The roots of upper back teeth sit right below the maxillary sinus. An infection at the tip of one of these roots can cause one-sided sinus pressure, a blocked nose on one side, or post-nasal drip with a bad smell. If you have “sinusitis” on one side that keeps coming back and you have a root canal tooth on that side, mention it to both your doctor and your dentist.
How Serious Is It? What to Do for Each Sign
| What you notice | What to do |
| Mild soreness that improves each day | Normal. Keep up home care. |
| Biting tenderness lasting over 2 weeks, or a gum bump | Book a dental visit within a few days |
| Swelling growing after day 3, pain getting worse, or a bad taste | Call your dentist today |
| Fever, chills or swollen glands with facial swelling | Same-day dental or urgent care visit |
| Swelling near the eye or in the neck, trouble swallowing, breathing or opening your mouth | Go to the emergency room or call 911 |
Rarely, a dental infection spreads into the floor of the mouth and neck, a condition called Ludwig angina, which can block the airway. Signs of sepsis, such as confusion, a racing heart, shortness of breath or clammy skin, are also an emergency. For urgent dental problems, see our emergency dentist page.
What Happens When You See Your Dentist
A visit for a suspected root canal infection usually includes:
- Questions about when symptoms started and how they have changed
- Checking the gum, the bite and the crown or filling
- Tapping and bite tests on the treated tooth and its neighbors
- A new X-ray compared with earlier ones, and sometimes a 3D scan
- Tracing a gum bump to find exactly which root it is coming from
Depending on the cause, treatment may involve draining the infection, root canal retreatment, a minor surgery called an apicoectomy, or removing the tooth and replacing it with a dental implant. Antibiotics are used when an infection is spreading, but the American Dental Association advises that they do not replace treating the tooth itself. For the full picture, read our guide to root canal vs. implant.
What You Can Do Until Your Appointment
- Take ibuprofen or acetaminophen as directed on the label, if these are safe for you.
- Rinse with warm salt water a few times a day.
- Chew on the other side and avoid hard or sticky foods.
- Use a cold pack on your cheek for 15 to 20 minutes at a time if there is swelling.
- Do not squeeze a gum bump, and do not put aspirin or other tablets directly on the gum.
- Do not use leftover antibiotics from a previous prescription.
How to Lower the Risk of Infection After a Root Canal
- Get the permanent crown or filling placed promptly after treatment.
- Keep your follow-up X-ray visits, even if you feel fine.
- Protect the tooth from heavy forces. A night guard helps if you clench or grind.
- Brush, floss and have regular dental exams, so decay around crowns is caught early.
- Call early. Small problems found early are much easier to fix.
Worried About Your Root Canal? We Can Help in Beverly Hills
If you have noticed any of these signs, you do not have to guess. At ConfiDental Beverly Hills we examine the tooth, compare your X-rays, explain what we find in plain language and offer same-day visits for swelling or pain. We are happy to give a second opinion on a root canal done elsewhere.
Book a visit or call (310) 858-9212.
Frequently Asked Questions
How do I know if my root canal is infected?
Look at the trend. Pain or swelling that gets worse after the first few days, a gum bump, a bad taste, tenderness that will not fade, or fever are the main signs. An X-ray confirms it.
How soon after a root canal can an infection show up?
Signs can appear within days if the original infection was not fully cleared, or months to years later if bacteria leak back into the tooth.
Can a root canal get infected years later?
Yes. A worn filling, a loose or leaking crown, new decay or a root crack can let bacteria back in, even many years after a successful root canal.
What are the symptoms of infection under a root canal with a crown?
Tenderness when biting, a gum bump or swelling near the crown, a bad taste, bleeding or dark gums at the crown’s edge, and a crown that feels loose.
Does an infected root canal always hurt?
No. Because the nerve has been removed, many infections are painless and only show up as a gum bump or on an X-ray.
Can an infection after a root canal spread?
Yes. Untreated, it can spread to the jaw bone, the face and the neck. Swelling near the eye or neck, trouble swallowing or breathing, or a high fever needs emergency care.
Can a root canal infection make you feel sick or tired?
It can. Fever, chills, fatigue and swollen glands suggest the infection is affecting your body more widely, and you should see your dentist the same day.
Is a darker tooth after a root canal a sign of infection?
Not by itself. Root canal teeth often darken over time as the inside of the tooth changes. Darkening with pain, swelling or a gum bump does need checking. Cosmetic options are covered on our stained teeth treatment page.
Why is my root canal tooth sensitive to cold?
A fully treated tooth should not feel temperature. Cold sensitivity can mean a canal still contains nerve tissue, or that a neighboring tooth is the real source of the pain.
Can I treat a root canal infection at home?
No. Salt water rinses and pain relievers can ease symptoms, but the bacteria are inside or around the tooth and need professional treatment.
Will antibiotics cure an infected root canal?
Antibiotics can calm a spreading infection, but they cannot reach bacteria inside a root-filled tooth. The infection usually returns unless the tooth itself is treated. Read more about tooth abscess symptoms and treatment.
About the Author
Dr. Liyan Massaband, DMD, MPH leads ConfiDental Beverly Hills. She earned her Doctor of Dental Medicine from Midwestern University and her Master of Public Health from the University of Southern California. In more than 15 years of practice she has completed over 1,000 implant procedures and focuses on full-mouth restoration, complex cases and prevention-first care.
References
- American Association of Endodontists. Root Canal Post-Treatment Care.
- American Dental Association. Antibiotics for Dental Pain and Swelling Guideline.
- Ludwig angina. U.S. National Library of Medicine.
- Centers for Disease Control and Prevention. About Sepsis.
This article is for general education and is not a substitute for an examination. If you have symptoms, please contact a dentist or doctor.