Lockjaw starts with stiffness in the jaw that progresses to a visible inability to open the mouth, caused by rigid, involuntary clenching of the chewing muscles. The jaw appears locked shut, and the person’s face may contort into a grimace that resembles a forced smile. This is the hallmark of tetanus, a bacterial infection that causes muscles throughout the body to seize up, and knowing what it looks like can help you recognize it early.
What the Face Looks Like
The most recognizable sign is trismus: the jaw muscles clench so tightly that the person physically cannot open their mouth, or can only open it a small amount. The muscles along the sides of the jaw look visibly tense, and the teeth may be clamped together. Trying to force the mouth open doesn’t work because the muscles are in sustained, involuntary contraction.
As the facial muscles become involved, a distinctive expression develops called “risus sardonicus,” which translates roughly to “sardonic smile.” It looks like a painful, frozen grin. The eyebrows may be raised, the forehead wrinkled, and the corners of the mouth pulled wide and upward, all while the jaw remains clenched. It’s not a voluntary expression. The combination of a locked jaw with this eerie smile-like grimace is one of the most recognizable features of tetanus.
How Spasms Spread Beyond the Jaw
Tetanus typically begins with mild spasms in the jaw and then moves to the neck, chest, back, and abdominal muscles. The neck becomes stiff and difficult to turn. The abdominal wall can feel board-like and rigid to the touch. These aren’t brief twitches. They’re sustained contractions that hold muscles in a locked position for extended periods, sometimes punctuated by sudden, violent spasms triggered by noise, light, or touch.
In severe cases, the back muscles contract so forcefully that the entire body arches backward in a posture called opisthotonus. The head tilts back, the spine curves dramatically, and the legs extend straight out. The arching can be so extreme that the person’s trunk lifts off the surface they’re lying on. This posture results from simultaneous contraction of all the extensor muscles along the spine.
Why the Muscles Lock Up
The bacterium that causes tetanus (found in soil, dust, and animal waste) produces a toxin that travels along nerves to the spinal cord. There, it silences the neurons responsible for telling muscles to relax. Normally, your nervous system balances “contract” and “relax” signals to control movement. The toxin blocks the “relax” signals, leaving motor neurons in a state of constant excitation. The result is rigid paralysis: muscles contract continuously with no off switch.
This is why the jaw muscles are often affected first. They’re controlled by short nerve pathways that the toxin can reach quickly. As the toxin spreads to more inhibitory neurons in the spinal cord, more muscle groups lose their ability to relax, and the rigidity moves downward through the body.
Early Signs Before Full Lockjaw Develops
Symptoms usually appear 3 to 21 days after the bacteria enter the body through a wound, with most cases showing up within 14 days. The average incubation period is about 10 days. Early on, you might notice jaw stiffness that feels like difficulty chewing or a sore jaw. This can be easy to dismiss as a dental problem or stress-related clenching.
Other early signs include neck stiffness, difficulty swallowing, and a general sense of restlessness or irritability. Muscle stiffness near the wound site can also appear before the jaw symptoms become obvious. By the time the jaw is visibly locked and the facial grimace appears, the infection has progressed significantly.
Breathing Complications
The most dangerous progression happens when muscle rigidity reaches the chest and throat. The vocal cords can tighten uncontrollably (laryngospasm), and the muscles between the ribs and the diaphragm can become too rigid to expand the lungs properly. Breathing becomes visibly labored, shallow, or interrupted by sudden spasms. This is the complication most likely to be life-threatening, and it’s the reason severe tetanus cases require mechanical ventilation.
How Lockjaw Is Identified
There’s no quick blood test for tetanus. Diagnosis is based almost entirely on what the person looks and feels like. One bedside test involves touching the back of the throat with a flat spatula. In a healthy person, this triggers a gag reflex that pushes the spatula out. In someone with tetanus, it triggers a reflex spasm of the jaw muscles that causes them to bite down on the spatula instead. A positive result on this test, combined with visible jaw rigidity and a recent wound, points strongly toward tetanus.
The wound itself doesn’t have to be dramatic. Tetanus has been diagnosed in people with small puncture wounds, scratches, or even wounds they don’t remember getting.
Who Is at Risk
Tetanus is preventable with vaccination, and it’s rare in countries with high immunization rates. The standard recommendation is one booster dose every 10 years throughout adulthood. Risk increases for anyone who hasn’t kept up with boosters, particularly older adults whose immunity has waned. If you sustain a wound and aren’t sure when your last tetanus shot was, that’s worth checking, especially for deep puncture wounds, wounds contaminated with dirt or rust, or injuries from objects outdoors.
People who garden, work with animals, or are frequently exposed to soil have more opportunities for the bacteria to enter through small cuts. The bacteria don’t spread from person to person. Every case comes from environmental exposure through broken skin.