What Is Lockjaw?

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Lockjaw, also known as trismus, is painful muscle contractions of the jaw and neck that restrict the range of motion of the jaw, causing it to "lock." As a result, a person experiencing lockjaw is unable to fully open their mouth.

People commonly think of lockjaw as a symptom of tetanus infection, but the muscle spasms of lockjaw can also occur from injury, periodontal infections, medication, or temporomandibular joint (TMJ) disorders.

This article describes the signs and symptoms of lockjaw as well as some of the common and uncommon causes. It also explains how lockjaw is diagnosed, and the various treatments used to relieve symptoms and resolve the underlying condition.

Symptoms of Lockjaw

The defining symptom of lockjaw is only being able to open your mouth about 35 mm (1.4 inches)—that's less than three fingers in width.

Lockjaw affects the whole jaw. The "locking" of the jaw is usually felt equally on both sides of the face. Lockjaw can come on suddenly, and the symptoms peak within a few hours.

Many nerves and muscles control the movement of your jaw. Lockjaw typically causes your jaw to be partially open because of where these nerves and muscles are located.

While not being able to open your mouth fully is the most common symptom of lockjaw, it's not the only symptom. Lockjaw can last from several hours to a few days. Within just a few hours, lockjaw can also cause:

Lockjaw can make your speech hard for others to understand. You may also have trouble swallowing because you cannot control your mouth's movement.

After about a day, lockjaw will start to affect your oral health because you will not be able to swallow your saliva normally or take care of your teeth.

This can lead to:

Complications of Lockjaw

Lockjaw that lasts for longer than a few days can affect your overall health. Complications of persistent lockjaw include:

  • Tooth decay and ulcers in your mouth because you can't brush and floss your teeth
  • Teeth grinding (bruxism) can cause your tooth enamel to wear away and even cause your teeth to crack
  • Malnutrition because you're having difficulty eating
  • Muscle stiffening that does not respond to treatment as quickly as a muscle spasm

What Causes Lockjaw?

Lockjaw occurs because a muscle remains in its active position and cannot relax (spasm). The muscle spasm that occurs with lockjaw can because be caused by many things.

For example, a spasm can happen when there is an injury to the muscle, nerve, bone, tendon, or ligament. It can also be related to health conditions, infections, and medications.

Verywell / Brianna Gilmartin

Temporomandibular Joint (TMJ) Disorders

Your temporomandibular joint (TMJ) is located at the sides of your face, below your eyes, and toward your ears. This joint is where the muscles, bones, tendons, and ligaments that control your jaw meet.

The TMJ allows you to chew food, speak, and yawn. TMJ disorders are chronic conditions that can lead to lockjaw.

TMJ can develop for multiple reasons, including:

If you experience lockjaw because you have TMJ, being dehydrated can trigger a flare or make your symptoms worse.

Lockjaw from TMJ can come back even after the initial discomfort of the chronic condition goes away.

Oral Infections

Infections around your mouth or jaw muscles, such as a peritonsillar abscess, can affect the jaw's movement. When this happens, lockjaw can occur.

In rare instances, your nerve or muscle can become permanently damaged from an infection. If it does, you might be more likely to experience recurrent episodes of lockjaw.


Some medications can affect nerve function and lead to lockjaw. The most common culprits are anti-nausea medications, such as Reglan (metoclopramide), and some antipsychotic medications.

Rarely, anesthetics can cause a rare condition called malignant hyperthermia. This complication is a severe reaction where a person gets a high body temperature and rapid heart rate. In addition, it can involve muscle spasms, including lockjaw.


Cancer and some cancer treatments (e.g., surgery, radiation) can cause injuries to parts of the jaw that control movement.

There are a few risk factors for developing lockjaw during cancer treatment:

  • Head or neck cancer
  • Surgery for head or neck cancer
  • Radiation treatment for head or neck cancers

If you have head or neck cancer or have had treatment for these types of cancers, you have about a 30% chance of developing lockjaw.


In the past, the term lockjaw was used as another name for tetanus, a serious bacterial infection. Lockjaw is now defined as the sustained locking of the jaw by any cause. This could include trauma, surgery, medication side effects, mouth infections, dental problems, and cancer or cancer treatment,

Lockjaw can be extremely painful and, in some cases, life threatening. When tetanus is involved, lockjaw can lead to complications such as choking, the inability to breathe, and death.

Tetanus occurs when a person is exposed to a life-threatening neurotoxin that's released by a bacterium. The bacterium, Clostridium tetani, is commonly found in the environment.

Lockjaw used to be called tetanus.

Tetanus toxin can cause muscle spasms in several muscle groups, including:

  • Heart muscles
  • Chest muscles (which impairs breathing)
  • Facial muscles (including those of the jaw)
  • Any voluntary muscles in the body

Tetanus is a significant risk factor for lockjaw. Most people with tetanus experience it.

However, tetanus is extremely rare in most parts of the world because there are routine immunizations and booster shots that protect against the infection.

Other Medical Conditions

Low calcium levels (hypocalcemia) are another common cause of lockjaw. This complication can sometimes happen during thyroid surgery.

Nerve or muscle diseases can also cause muscle spasms. For example, a rare autoimmune disorder called stiff person syndrome can cause spasms in any voluntary muscle, including in the jaw.

How Is Lockjaw Diagnosed?

Providers can diagnose lockjaw based on your medical history and a physical examination.

However, lockjaw can make it hard for you to verbally explain your symptoms because you are not able to speak clearly. You may need to write down your symptoms or have someone else give your medical history to a provider.

Physical Examination

Most healthy people can open their mouths between 35 to 55 millimeters (mm) or 1.4 to 2.2 inches wide. If you're experiencing lockjaw, you might only be able to open your mouth less than 35 mm (1.4 inches)—or less than three fingers in width.

Your healthcare provider will measure how wide your mouth can open to see if you fall in or out of the typical range.

Your provider will also look for other signs of lockjaw, such as:

  • Your ability (or inability) to close your mouth all the way
  • Trouble moving your jaw
  • Stiffness and tightness of your jaw muscles
  • Clenched teeth


If there is a concern that you could have an injury, infection, or tumor affecting your mouth, face, or jaw, you may need more diagnostic testing.

Imaging studies can often identify lesions in and around the jaw. They might include:

You may need to have a piece of a tumor removed so that it can be looked at more closely with a microscope (biopsy).

Treatment for Lockjaw

Lockjaw can often be treated with an oral or injected muscle relaxant. Physical therapy is also commonly part of a treatment plan for lockjaw.

If you have another condition that's causing lockjaw, you'll need treatment for that as well. For example, if you have an infection, you may need to take antibiotics.

You may need to work with different healthcare providers to treat lockjaw, such as:

If a medication you're taking caused your muscle spasm, your provider will likely recommend that you stop. However, never stop a medication without your provider's OK.

Spasm Relief

Oral and injected muscle relaxants are typically helpful for lockjaw.

Common examples of oral medications that relax muscles include:

However, these medications may cause side effects such as drowsiness.

Targeted injections for lockjaw, including botulinum toxin (Botox) or anti-inflammatory steroids, can help relax the muscle and relieve the spasm. The injections do not cause the body-wide side effects that can happen with medications.

Physical Therapy

In addition to medical management, you may need to have physical therapy or speech therapy for lockjaw. Your therapist may also suggest at-home exercises to improve control of your jaw muscles.

If you're doing at-home therapy for lockjaw, don't push yourself so hard that the exercises are painful.

Treating the Underlying Cause

Since there's a wide range of conditions that can cause lockjaw, there's also a range of treatments that might be required to address them. For example:

  • Oral or intravenous (IV) antibiotics for infections
  • Anti-inflammatory treatment for TMJ
  • Radiation or surgery for tumors

If radiation therapy or surgery is the cause of your lockjaw, then physical therapy might be the most effective treatment approach. However, longstanding lockjaw after radiation therapy can be very hard to reverse.

Preventing Lockjaw

If you have experienced lockjaw, you are at risk for developing it again. It's important to discuss prevention with your healthcare provider.

Preventative strategies for lockjaw may include avoiding medications that trigger it, getting treatment for TMJ or other conditions you have, and doing regular exercise of your jaw muscles.

Most importantly, if you notice the symptoms of lockjaw, call your provider as soon as possible.


Lockjaw is a condition where the muscles in the jaw affect its movement. The mouth is not able to open as widely as usual, which can affect speech and swallowing.

Infections, health conditions, injury, and medications can cause lockjaw.

Treatment for lockjaw is aimed at relaxing the muscles and getting the moving normally again, as well as addressing the root cause of the spasm. Physical therapy and medication are common components of a treatment plan for lockjaw.

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Additional Reading

By Kristin Hayes, RN
Kristin Hayes, RN, is a registered nurse specializing in ear, nose, and throat disorders for both adults and children.