Lockjaw is caused by a bacterial infection called tetanus, though it can also result from jaw injuries, dental procedures, or joint disorders. The term most commonly refers to tetanus, where a toxin produced by bacteria in contaminated wounds triggers uncontrollable muscle spasms, starting with the jaw. The bacteria live in soil, dust, and animal feces, and enter your body through breaks in the skin.
How Tetanus Bacteria Enter Your Body
The bacterium responsible for tetanus, Clostridium tetani, exists as spores in the environment, particularly in dirt and soil. These spores get into your body through broken skin. The wounds most likely to cause tetanus include puncture wounds from objects like nails or needles, injuries contaminated with dirt or feces, and wounds involving dead tissue such as burns, crush injuries, or frostbite.
Less obvious entry points include chronic skin sores, dental infections, insect bites, and intravenous drug use. Surgical procedures can also introduce the bacteria in rare cases. You don’t catch tetanus from another person. It always comes from the environment entering a wound.
What the Toxin Does to Your Muscles
Once inside a wound, the bacteria produce a powerful toxin that travels along your nerves to the spinal cord and brainstem. There, it blocks the release of chemicals that normally keep your muscles relaxed. Without those calming signals, your motor neurons fire without any off switch, causing muscles to contract and lock up involuntarily.
The jaw muscles are typically affected first because they have shorter nerve pathways from common wound sites. This is why the condition earned the name “lockjaw.” As the toxin spreads, spasms can move to the neck, back, abdomen, and limbs. In severe cases, the muscle contractions are strong enough to cause breathing difficulty or fractures.
Symptoms and How Quickly They Appear
Tetanus symptoms usually develop within 3 to 21 days after infection, with most cases appearing around 10 days. The first sign is typically stiffness in the jaw, making it difficult to open your mouth or chew. This is followed by stiffness in the neck and difficulty swallowing.
As the infection progresses, you may experience painful body spasms triggered by minor stimuli like a loud noise, a draft of air, or being touched. Fever, sweating, and elevated blood pressure often accompany the spasms. The earlier symptoms appear after a wound, the more severe the case tends to be.
How Doctors Identify It
There’s no blood test or lab work that confirms tetanus. Doctors diagnose it based on your symptoms and physical exam, combined with your vaccination history and any recent wounds. One diagnostic tool is the spatula test: a doctor touches the back of your throat with a soft instrument. Normally this triggers a gag reflex, but in someone with tetanus, it causes the jaw to clamp shut involuntarily instead.
How Dangerous Is Tetanus?
Tetanus is rare in the United States but still deadly when it occurs. Between 2009 and 2023, 402 cases were reported nationwide, with an overall fatality rate of about 12%. Deaths were concentrated among older adults and people who had never completed a full vaccination series. In that 15-year span, no one who had received three or more vaccine doses died from the infection. Among those who received a preventive immune treatment after a wound, no deaths were reported either.
Vaccination Is the Primary Defense
The tetanus vaccine is given as part of the DTaP series in childhood, with a booster (Tdap or Td) recommended every 10 years throughout adulthood. If you sustain a wound that’s dirty, deep, or involves dead tissue and your last booster was more than five years ago, a dose is typically given as part of wound care. Pregnant individuals receive one dose of Tdap during each pregnancy to protect the newborn.
Keeping up with boosters is the single most effective way to prevent lockjaw. The 15-year surveillance data from the CDC makes this point starkly: adequate vaccination eliminated the risk of death entirely in reported cases.
Other Causes of Jaw Locking
Not every case of a stiff or locked jaw means tetanus. The medical term for restricted jaw movement is trismus, and it has several causes unrelated to tetanus.
- Temporomandibular joint disorders (TMD): Problems with the jaw joint itself are one of the most common reasons people experience jaw locking or clicking. This is often related to stress, teeth grinding, or joint misalignment.
- Wisdom tooth removal: Having your jaw held open during oral surgery can lead to temporary trismus, particularly after lower wisdom teeth extraction.
- Head and neck cancer treatment: Radiation therapy to the head or neck can cause scarring in the jaw muscles, leading to long-term difficulty opening the mouth.
- Infections: Dental abscesses, tonsillitis, mumps, and infections of the salivary glands can all trigger jaw stiffness through inflammation.
- Trauma: A direct blow to the jaw or face can cause swelling and muscle guarding that limits how far you can open your mouth.
The key difference is context. Tetanus-related lockjaw comes with a recent wound, progresses to affect other muscle groups, and involves involuntary spasms. TMD or post-surgical trismus stays localized to the jaw area and doesn’t come with fever or full-body symptoms. If your jaw suddenly becomes stiff after a wound or injury and you can’t remember when your last tetanus shot was, that combination warrants urgent medical attention.