Symptoms Of A Root Canal That Is Infected

An infected root canal causes pain, swelling, and a bad taste that does not go away. These symptoms mean bacteria have reached deep inside your tooth. Treatment can stop the infection and often save the tooth.

7 min readMedically reviewed by MSD Clinical Editorial TeamLast updated June 19, 2026

Key Takeaways

Lasting pain and swelling are the most common signs of an infected root canal, and they usually mean bacteria have reached the inner tissue of the tooth ^[4].
Antibiotics alone do not cure the infection. Research shows the source of infection must be removed through dental treatment, not pills alone ^[5].
An infected root canal left untreated can spread. In rare cases, an untreated dental infection leads to a serious body-wide illness ^[10].
Root canal therapy removes the harmful bacteria inside the tooth, and several case-specific factors affect whether treatment or retreatment succeeds ^[8].
A bad taste and chronic bad breath can be common signs that infected fluid is draining from the tooth, so they are worth reporting to your dentist ^[11].
Experts agree pain relief and healing are core goals of endodontic treatment, which is why early care matters for your oral health ^[6].

What an Infected Root Canal Is

An infected root canal happens when bacteria invade the soft tissue inside a tooth, called the pulp, causing pain, swelling, and sometimes drainage. The pulp holds nerves and blood vessels. When harmful bacteria reach it, the body cannot clear them on its own.

The word "root canal" means two things. It is the natural space inside the tooth root. It is also the name of the root canal procedure that cleans out that space. When people say they have an infected root canal, they may mean a tooth that needs treatment, or a treated tooth that became reinfected. Either way, an infected root canal threatens your oral health and needs care.

Pulp inflammation is the first stage of the problem. Deep decay, a crack, or repeated dental work lets bacteria reach the pulp. The pulp swells and the body sends immune cells to fight back ^[4]. If the bacteria win, the pulp dies and the infection moves down toward the tip of the root and into the surrounding bone.

Common Signs and When Treatment Is Recommended

Treatment is recommended when an infected root canal causes ongoing symptoms or shows infection on a dental X-ray. The most common signs point to bacteria deep inside the affected tooth. Catching these signs early gives you more treatment choices.

Many of these symptoms overlap with gum disease, so a dentist needs to examine the tooth to find the true source. Gum disease affects the tissue and bone around the tooth, while a root canal infection starts inside the tooth. Telling them apart matters because the treatments differ. Both can harm your overall health if ignored.

Severe pain or persistent pain when chewing or biting, or tooth pain that wakes you at night
Lasting sensitivity to hot or cold that does not fade after the food or drink is gone
Swelling in the gum, face, or jaw near the affected tooth
A pimple-like bump on the gum that may leak pus and leave a bad taste
Bad taste in the mouth or chronic bad breath that does not improve with brushing
Darkening of the tooth compared to the teeth around it
Tender, swollen lymph nodes under the jaw or in the neck

What Happens When an Infected Root Is Left Untreated

An infected root that is left untreated does not get better on its own. The infection can spread into the jawbone and cause bone loss around the tooth root. Bone loss can loosen the tooth and make it harder to save later.

When an infection is left untreated for a long time, the bacteria can move beyond the mouth. In rare cases, an untreated dental infection has led to a serious whole-body illness ^[10]. This is uncommon, but it shows why these symptoms should not be ignored. A spreading infection that causes fever, trouble swallowing, or swelling that closes the eye needs same-day care.

What to Expect During Root Canal Treatment

Root canal treatment removes the infected pulp, cleans the inside of the tooth, and seals it to keep bacteria out. The goal is to stop the infection and keep your natural tooth. Most cases are finished in one or two visits.

Before: Exam and Diagnosis

Your dentist or endodontist starts with an exam and a dental X-ray. The X-ray shows the shape of the roots and any sign of infection in the bone. The dentist may tap on the tooth or test it with cold to confirm the source of the pain.

If you have heavy swelling, the dentist may need to drain the area first. Antibiotics are sometimes given when the infection has spread into the face or when you have a fever. On their own, though, antibiotics do not fix the problem. Research shows that the source of infection must still be removed through dental treatment ^[5].

During: The Root Canal Procedure

The area is numbed so the root canal procedure feels much like a deep filling. The dentist places a thin sheet to keep the tooth dry, then makes a small opening in the top of the tooth. Through that opening, they remove the infected pulp and the harmful bacteria inside each canal.

Next, the canals are shaped and cleaned with small files and rinses. The dentist fills the empty space with a rubber-like material and seals the opening. A crown is often added later to protect the tooth, since a back tooth takes heavy force when you chew. Several case-specific factors affect how well root canal therapy works, including how curved the roots are and how much infection was present ^[8].

After: The First Hours

Once the numbness wears off, the tooth and gum may feel sore for a few days. This is a normal part of healing. Over-the-counter pain medicine usually controls it. Pain relief and healing are core goals that endodontic experts use to judge whether treatment succeeded ^[6].

Recovery and Aftercare Timeline

Most people return to normal activities the same day, with soreness fading over about a week. Knowing what is normal helps you spot the rare problem early. Follow your dentist's instructions on chewing and medicine.

Day 1: Mild soreness and tenderness are normal. Avoid chewing on that side until the numbness is fully gone. Take pain medicine as directed.
Week 1: Soreness should fade steadily. You can usually chew softly on the tooth. A temporary filling may feel slightly different until the permanent crown is placed.
Month 1: The tooth should feel normal. If a crown was planned, this is often when it is placed. Healing in the bone around the root continues for months and is checked at follow-up visits.

Normal vs. Call the Office

Mild soreness, slight swelling, and tenderness for a few days are normal after the root canal procedure. These signs should improve, not get worse. Keep brushing gently and rinse as your dentist suggests to protect your oral health.

Call the office if pain grows stronger after day three, if swelling spreads, if you develop a fever, or if a bad taste returns. These can be common signs that the infection is not fully gone. Returning symptoms may point to a failed root canal that needs a closer look.

Cost, Insurance, and Financing

Root canal treatment in the United States often ranges from about $700 to $1,800 per tooth, with front teeth at the lower end and molars at the higher end. Costs vary by location, provider, and case complexity. A crown to protect the tooth afterward is usually a separate charge, often $1,000 to $2,500.

Retreatment of a failed root canal and treatment by a specialist tend to cost more than a first-time procedure on a simple tooth. The number of canals, the need for a crown, and the difficulty of the case all change the price. Always ask for a written estimate before treatment begins.

Many dental insurance plans cover part of root canal therapy, often paying a share after your deductible. Coverage limits and waiting periods differ by plan. If you do not have insurance, ask the office about payment plans, dental schools, or third-party financing. Treating an infected root canal early is often less costly than waiting until the tooth must be removed and replaced.

Specialist vs. General Dentist

Many general dentists treat straightforward root canal infections, while complex cases are often sent to an endodontist, a dentist with extra training in the tooth's inner tissue. The right choice depends on the tooth and your history. Your dentist can tell you which path fits your case.

An endodontist is often the better choice for a tooth with curved or narrow roots, for a failed root canal that needs retreatment, or when earlier treatment did not solve the pain. Endodontists use magnification and detailed imaging to treat hard cases. They focus almost entirely on saving teeth, so they handle infected root canal cases every day.

See a dentist promptly for any tooth pain, swelling, or a bad taste that does not clear. Fast care protects not just the tooth but your overall health, since an infection in the mouth can affect the rest of the body. Routine checkups also catch problems before they reach the pulp ^[12].

Find an Endodontist Near You

If you have signs of an infected root canal, a specialist can examine the tooth and explain your options. Learn more about this field of care on the endodontics page, then use our directory to find an endodontist near you. Early treatment gives you the best chance to keep your natural tooth and protect your oral health ^[11].

Search Endodontists in Your Area

Frequently Asked Questions

How do I know if my root canal is infected?

The most common signs are pain that lasts, swelling near the tooth, a gum bump that leaks pus, and a bad taste or chronic bad breath. These point to bacteria deep in the tooth ^[4]. Only a dental exam and X-ray can confirm an infected root canal, since the same symptoms can come from gum disease ^[12].

Can an infected root canal heal on its own?

No. Once bacteria reach the pulp, the body cannot clear the infection without treatment. Antibiotics may ease symptoms for a short time, but research shows the source of infection still must be removed through dental treatment ^[5]. The infection returns or spreads if the tooth is not treated.

What happens if an infected root canal is left untreated?

An infected root left untreated can spread into the jaw and cause bone loss around the tooth. The tooth may loosen or need to be removed. In rare cases, an untreated dental infection has led to a serious whole-body illness ^[10], which is why these symptoms should not be ignored.

Is an infected root canal a dental emergency?

It can be. Mild, steady tooth pain should be seen soon but is not always urgent. Seek same-day care if you have spreading facial swelling, a fever, trouble swallowing, or swelling that closes an eye. These are common signs that the infection is moving beyond the tooth and threatening your overall health ^[11].

Can a root canal get infected years later?

Yes. A treated tooth can become reinfected if bacteria leak back in through a worn crown, new decay, or a crack. This is sometimes called a failed root canal. Several factors affect whether the first treatment lasts ^[8]. Retreatment can often clean and reseal the tooth and save it.

Does treating an infected root canal hurt?

The root canal procedure is done with local numbing, so it usually feels much like a deep filling. Most of the pain comes from the infection itself, not the treatment. Pain relief is a core goal of endodontic care ^[6]. Some soreness for a few days afterward is normal and eases with over-the-counter medicine.