The Babinski reflex is a neurological test in which stroking the sole of the foot reveals whether the nerve pathway connecting the brain to the spinal cord is working properly. In a healthy adult, the toes curl downward in response. When the big toe extends upward instead, that upward movement is called a positive Babinski sign, and it suggests damage somewhere along that pathway. In infants and children up to about 2 years old, the upward response is completely normal.
How the Test Works
A clinician runs a firm, blunt object (typically the handle of a reflex hammer or a tongue depressor) along the outer edge of the sole, starting at the heel and sweeping forward toward the ball of the foot. The pressure needs to be uncomfortable enough to trigger a reflex but not hard enough to cause injury. The stroke stays along the lateral edge and doesn’t cut across the middle of the sole, because stimulating that area can accidentally trigger a different reflex and muddy the results.
There are two possible responses. In a normal (negative) result, the toes flex downward, curling toward the sole. In an abnormal (positive) result, the big toe bends upward while the remaining toes may splay apart in what’s sometimes called the “fan sign.” The entire test takes a few seconds and requires no equipment beyond something to stroke the foot with.
Why the Big Toe Moves Upward
Your brain sends movement commands down to your limbs through a bundle of nerve fibers called the corticospinal tract. This tract also keeps certain primitive reflexes in check. When the tract is intact, the brain suppresses the upward toe response and produces the normal downward curl. When the tract is damaged by injury, disease, or compression, that suppression is lost, and the big toe extends upward instead. In other words, a positive Babinski sign doesn’t point to a foot problem. It points to a problem somewhere between the brain and the spinal cord.
Normal in Babies, Abnormal in Adults
Newborns and young children haven’t finished developing the corticospinal tract, so the upward toe response is expected. It’s one of several primitive reflexes pediatricians check during routine exams. The Babinski reflex typically disappears as early as 12 months and is generally gone by age 2 as the nervous system matures. After that age, a positive response is no longer considered normal and warrants further investigation.
What a Positive Sign Can Mean
In adults, a positive Babinski sign signals that something is interfering with the corticospinal tract. The sign itself doesn’t identify a specific disease, but it narrows the search to conditions that affect upper motor neurons, the nerve cells that run from the brain down through the spinal cord. Common causes include:
- Stroke: interrupted blood flow damages brain tissue, including motor pathways
- Spinal cord injury or compression: trauma, herniated discs, or tumors pressing on the cord
- Multiple sclerosis: the immune system attacks the protective coating on nerve fibers
- ALS (amyotrophic lateral sclerosis): progressive degeneration of motor neurons
- Brain or spinal cord tumors: growths that press on or invade the tract
A positive sign on one side of the body often suggests a problem on the opposite side of the brain, because the corticospinal tract crosses over from one side to the other as it descends from the brain into the spinal cord.
How Reliable the Test Is
The Babinski reflex is one of the most widely used bedside neurological tests, but it isn’t perfect. In a study of 375 patients, the test had a sensitivity of about 50% and a specificity of roughly 86%. That means it correctly identifies damage about half the time (missing the other half), but when it does come back positive, it’s right the large majority of the time. A negative result doesn’t rule out a problem, but a positive result is a strong signal that something is going on.
False positives can also occur. People who are very ticklish, who have heightened skin sensitivity on the soles of their feet, or who have involuntary movement disorders may show an upward toe response that isn’t related to corticospinal tract damage. Clinicians can distinguish a true positive from a false one by checking whether the hamstring muscles on the back of the thigh contract at the same time. In a true Babinski response, they do. In a false one, they typically don’t.
Alternative Tests for Uncertain Results
When the standard Babinski test produces an unclear or borderline result, clinicians can turn to variations that stimulate different areas of the leg or foot to provoke the same upward toe response. The two most common alternatives are the Chaddock test, which involves stroking the skin just below the outer ankle bone, and the Oppenheim test, which involves stroking down the inner shin. Both look for the same upward big toe movement.
Research shows the Chaddock test performs comparably to the standard Babinski in terms of sensitivity and accuracy, making it a useful backup when the sole of the foot can’t be tested or the result is ambiguous. Agreement between these different tests is relatively weak, though, which is why clinicians often use more than one version and combine the results with other neurological findings rather than relying on any single test in isolation.
A Brief History
The reflex is named after Joseph Babinski, a French neurologist of Polish descent who first described it in 1896. His original report was remarkably short, just 28 lines, and detailed the upward toe movement he observed in patients with paralysis on one side of the body. Two years later, he refined his observation and linked the sign specifically to damage in the corticospinal tract rather than brain or spinal cord damage in general. In 1903, he added a description of the fanning of the smaller toes, calling it the “fan sign.” More than a century later, the Babinski sign remains one of the most recognized and frequently tested reflexes in clinical neurology.