A dermatome map is a diagram of the human body showing which patches of skin are connected to which spinal nerves. Each patch, called a dermatome, receives its sensation from a single spinal nerve root. The map labels these zones from the top of the skull down to the feet, giving clinicians a visual guide to trace skin sensations back to a specific level of the spine.
How Dermatomes Work
Your spinal cord runs through the center of your vertebrae, and 31 pairs of spinal nerves branch out from it, passing through small gaps between the bones. Each nerve exits left and right, then travels outward to supply sensation to a defined strip or region of skin. That region is its dermatome. Every signal you feel in that area, whether it’s pressure, temperature, or pain, travels along that nerve back to the spinal cord and up to the brain.
The spinal nerves are grouped by the section of spine they exit from: 8 cervical (C1 through C8) in the neck, 12 thoracic (T1 through T12) in the mid-back, 5 lumbar (L1 through L5) in the lower back, and 5 sacral (S1 through S5) near the tailbone. A dermatome map labels each skin zone with the corresponding nerve, so “T4” on the map means the skin in that area is wired to the fourth thoracic spinal nerve.
Key Landmarks on the Map
Certain dermatomes line up with easy-to-remember body landmarks that are widely used in clinical exams:
- C6: the thumb
- T4: the nipple line
- T10: the belly button
- L4: the front of the knee and inner ankle
Cervical dermatomes cover the head, neck, shoulders, arms, and hands. The thoracic dermatomes wrap around the torso in roughly horizontal bands, which is why they’re sometimes described as stacking like rings around the trunk. Lumbar and sacral dermatomes cover the hips, legs, feet, and groin. The pattern runs in a logical sequence from top to bottom, though the exact boundaries shift depending on the individual.
Why More Than One Map Exists
There is no single universally agreed-upon dermatome map. Early maps were created from experiments on cadavers, monkeys, and human patients before 1948, producing versions that were similar but not identical. In 1948, researchers Keegan and Garrett published a radically different version with long, swirling dermatome shapes. Their map was based on observing patients with disc herniations compressing individual nerve roots, a very different method than the surgical nerve-cutting techniques used by earlier mapmakers.
These competing maps still appear in different textbooks and clinical tools. The American Spinal Injury Association (ASIA) standardized one version for use in spinal cord injury assessment, which tests sensation at specific key points on each side of the body using pinprick and light touch. This is the closest thing to an “official” clinical standard, but other versions remain common in medical education.
Adjacent Dermatomes Overlap
One important detail the map doesn’t fully capture is that neighboring dermatomes share territory. The skin in any given area typically receives some nerve input from the spinal level above and below, not just from one nerve root alone. This overlap means that if a single nerve root is damaged, you may not lose all sensation in that dermatome, because the neighboring nerves partially compensate. It also means that the neat, color-coded boundaries on a printed map are approximations, not hard lines.
What Dermatome Maps Are Used For
The practical value of a dermatome map is working backward from symptoms to find their source. If you feel numbness, tingling, or a rash in a specific area, the map helps identify which spinal nerve is likely involved.
Shingles is the classic example. The varicella-zoster virus (the same virus that causes chickenpox) lies dormant in nerve cell clusters along the spine after your initial infection. When it reactivates, the virus travels down the nerve fiber and produces a painful, blistering rash in the skin area supplied by that nerve. This is why shingles almost always appears as a band on one side of the body, neatly following a single dermatome. The pattern is so characteristic that a dermatomal rash is often enough to diagnose shingles on sight.
Nerve root compression from a herniated disc is another common scenario. When a disc in the spine bulges and presses on a nerve root, you might feel pain, numbness, or tingling that radiates into the corresponding dermatome. Sciatica, for instance, often involves the L5 or S1 nerve roots and produces symptoms running down the back of the leg and into the foot.
Limits in Diagnosing Nerve Pain
The map is more reliable for some conditions than others. Research on patients with confirmed nerve root compression found that pain actually followed the expected dermatome pattern in only about a third of cases. In cervical radiculopathy (pinched nerves in the neck), roughly 70% of patients reported pain in non-dermatomal patterns. In the lumbar spine, about 64% had pain that didn’t match the textbook dermatome. The S1 nerve root was the notable exception: nearly 65% of patients with S1 compression felt pain along the expected S1 dermatome, making it the most diagnostically useful pattern.
This means clinicians can’t rely on the dermatome map alone to pinpoint which nerve root is compressed. Numbness tends to follow dermatomes more reliably than pain does, and imaging studies are usually needed to confirm the exact level of the problem.
Dermatomes vs. Myotomes
A dermatome covers sensation. A myotome covers movement. Each spinal nerve root supplies both a strip of skin (dermatome) and a group of muscles (myotome). For example, the C5 nerve root supplies sensation to the outer shoulder area and also powers the muscles that let you bend your elbow. Clinicians often test both together: if you’ve lost feeling in a dermatome and weakness in the matching myotome, that strongly points to a problem at that specific spinal level.
When you see a dermatome map, think of it as half of the picture. The sensory map and the motor map overlap and reinforce each other, giving a more complete view of spinal nerve function than either one alone.