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The term “dermatome” is a combination of two Ancient Greek words; “derma” meaning “skin”, and “tome”, a “cutting” or “thin segment”. It is an area of skin which is innervated by a single dorsal root of the spinal nerve. As dorsal roots are organised in segments, dermatomes are as well. This is why the term dermatome refers to the segmental innervation of the skin.

The dermatomes of neighbouring dorsal roots often overlap as the sensory peripheral branches corresponding to one root go way beyond the limit of their dermatome. As such, the thin lines seen in the dermatome maps are more of a clinical guide than a real boundary. This means that if a single spinal nerve is affected, there is likely still innervation to that segment of skin coming from above and below. For a dermatome to be completely numb, usually three neighbouring dorsal roots need to be affected.

Key facts about dermatomes
Development Develop from somites
Dermatome map Head, face and neck - trigeminal nerve (CN V) and spinal nerves C2-C4
Upper limbs - spinal nerves C5-T2
Thorax and abdomen - spinal nerves T3-T12
Lower limbs and genitalia - spinal nerves L1-S5
Clinical rotations Herpes Zoster (shingles), radicular pain

This article will discuss the development, distributions, and function of dermatomes.

  1. Anatomy
  2. Dermatome map
    1. Face, head and neck
    2. Upper limb
    3. Thorax and abdomen
  3. Lower limbs and genitalia
  4. Development
  5. Clinical relations
    1. Herpes Zoster
    2. Radicular pain
  6. Sources
+ Show all


Each somite has a corresponding spinal nerve, and by extension, a corresponding dorsal root of a spinal nerve that innervates a dermatome. Sensory information from the skin on the face is relayed via the trigeminal nerve (CN V). C1 is the only spinal nerve that does not have an associated dermatome as in many individuals, there is no dorsal root for spinal nerve C1.

Dermatomes are evenly spaced horizontally along the thorax and abdomen, and then they run in a different longitudinal pattern on the upper and lower limbs as you can see on a dermatome map. This difference is because of the way that the limbs bud and rotate during early embryonic development. To understand this distribution, imagine someone standing up straight and then leaning over to touch the floor with their fingertips. In this position, the dermatomes are aligned in the way they were prior to the rotation of limbs.

From anterior to posterior, dermatomes tend to dip more inferiorly than staying horizontal. As with all anatomy, there is natural variation among individuals. Natural variation can include intrathecal intersegmental anastomoses of dorsal spinal rootlets; an occurrence in which the sensory neurons of a dorsal nerve enter the spinal cord at a different level.

For more details about the dermatomes, including how to examine them, take a look below.

Dermatome map

Dermatome maps show the sensory distribution of each dermatome across the body. Clinicians can use test touch with a dermatome map as a way to localise lesions, damage, injury to specific spinal nerves, and to determine the extent of the injury, for example, if a patient is experiencing numbness in only one area. However, because of the overlapping segmentation of dermatomes, it is unlikely that numbness would occur if only one dorsal root is affected. Since the areas of skin are typically innervated by at least two spinal nerves, at least two neighbouring dorsal roots would need to be affected for numbness to occur. 

Want to learn the deramtomes as efficiently as possible? Make sure you're not making any of these common anatomy learning mistakes.

Face, head and neck

Dermatomes of the head, face, and neck include the trigeminal nerve (CN V), and spinal nerves C2-C4.

Upper limb

Dermatomes of the upper limbs are innervated by spinal nerves C5-T2. Here, the organisation of dermatomes is complex because of how the upper limbs bud in embryonic development.

  • C5 - anterior skin below the clavicles spreading over the lateral aspect of the upper limb, posterior skin around the base of the neck
  • C6 - shoulders and longitudinally down the middle posterior aspect of the upper limb, radial side of the hand, thumb
  • C7 - hand, middle finger
  • C8 - ulnar side of the hand, ring finger, and little finger
  • T1 - level of the infraclavicular fossa, extending to the medial aspect of the forearm
  • T2 - anterior and posteriorly extends at the level of the upper axilla and medial and upper aspect of the arm

Thorax and abdomen

The dermatomes of the thorax and abdomen are T3-T12. Anteriorly, each is quite evenly spaced, with T1-T9 being near horizontal lines, and T10-T12 having the lower borders dip inferiorly. Posteriorly, each is evenly spaced and oriented as infero-lateral sloped lines from the spine.

  • T3 - anterior and posteriorly extends at the level of the lower axilla 
  • T4 - anteriorly at the level of the nipple
  • T5 - anteriorly at the level just inferior to the nipple
  • T6 - anteriorly at the level of the xiphoid process
  • T7-T9 - evenly distributed anteriorly between T6 and T10 dermatomes
  • T10 - anteriorly at the level of the umbilicus
  • T11 - evenly distributed anteriorly between T10 and T12 dermatomes
  • T12 - anteriorly just superior to the pelvic girdle

Lower limbs and genitalia

The dermatomes of the lower limbs are distributed in spiral arrangements with segments L1-S5. This is because of how the limbs rotate to adapt an erect position during development. Of note, dermatomes S1, S4, and S5 are only on the posterior aspect.

  • L1 - posteriorly includes the skin lateral to L1 vertebra and wraps anteriorly to the groin and pelvic girdle area superior to the inguinal canal
  • L2 - anteriorly covers the thigh inferior to the inguinal canal
  • L3 - evenly spaced between L2 and L4, extending down the medial aspect of the thigh and leg
  • L4 - anteriorly curves from the lateral aspect of the thigh to the medial aspect of the leg and foot. Includes the knee, medial surface of big toe, and medial malleolus
  • L5 - posterolateral aspect of the thigh wrapping anteriorly at the level of the knee to cover the anterolateral aspect of the leg. Includes the dorsal and plantar aspects of the foot, lateral surface of the big toe, and toes, 2, 3, and 4
  • S1 - extends to the posterolateral aspect of thigh, popliteal region, and leg to the lateral malleolus, lateral margin of foot, heel, and little toe
  • S2 - extends from the buttocks to the posteromedial aspect of the thigh, popliteal region and leg. Anteriorly includes the penis and scrotum
  • S3 - posteriorly includes the medial aspect of buttocks, perineal area; anteriorly includes the penis and scrotum
  • S4 - perineal area , and genitals
  • S5 - perineal area, and skin of and adjacent to the anus


The rostrocaudal organisation of the spinal cord happens early in intrauterine development. Mesodermal tissue is divided into cubed-shaped, bilaterally paired segments called somites. There are 38-40 segments; 8 cervical segments, 12 thoracic segments, 5 lumbar segments, 5 sacral segments, and 8-10 coccygeal segments. Each somite will differentiate into three regions:

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