The skin covering the hand is not uniform, showing biological specialization where two adjacent surfaces serve distinct purposes. The palm, or volar surface, is designed for high-friction grip and detailed sensory exploration, requiring resilience and acute sensitivity. Conversely, the back of the hand, or dorsal surface, is adapted for flexibility, protection, and temperature regulation, featuring a thinner structure and different protective secretions.
Structural Anatomy: Glabrous vs. Hairy Skin
The primary distinction between the palm and the back of the hand is the presence or absence of hair, classifying them as glabrous and hairy skin, respectively. Palmar skin possesses an exceptionally thick epidermis, the outermost layer, which provides mechanical shielding against abrasion and pressure. This thickness is due to a substantial stratum corneum, reinforced by a unique epidermal layer called the stratum lucidum. The palmar skin is also anchored to underlying structures by the palmar aponeurosis, a fibrous layer that ensures stability during grasping movements.
In contrast, the dorsal skin features a much thinner overall epidermal layer. The back of the hand is covered in hair follicles, which are part of the pilosebaceous unit completely absent from the palm. Tiny arrector pili muscles are attached to these follicles, and their contraction causes the hair to stand erect, a mechanism associated with thermoregulation and the “goosebump” reflex.
Glandular Activity and Moisture Control
The two surfaces of the hand manage moisture and lubrication through different glandular systems. Palmar skin has an extremely high concentration of eccrine sweat glands, with densities ranging from 250 to 700 glands per square centimeter. These glands are primarily activated by the sympathetic nervous system in response to emotional or mental stress, often called emotional sweating. The moisture produced enhances friction between the hand and an object, improving grip stability.
The dorsal skin has a significantly lower density of eccrine sweat glands, sometimes as few as 65 per square centimeter, and these glands participate more in generalized body temperature regulation. The palm completely lacks sebaceous glands, the oil-producing glands common on the back of the hand. Sebaceous glands on the dorsal surface secrete sebum, an oily substance that lubricates the skin and hair, helping to maintain flexibility and preventing dryness.
Sensory Apparatus and Nerve Density
The palmar surface is equipped with a dense network of specialized mechanoreceptors. The palm and fingertips contain high concentrations of Meissner corpuscles, specialized nerve endings sensitive to light touch and flutter. These enable the fine discriminative touch necessary for identifying the texture and shape of manipulated objects. Slowly-adapting Merkel cells are also plentiful, providing continuous information about pressure and form.
The density of these receptors, particularly Meissner corpuscles, is highest in the fingertips and decreases proximally into the palm, correlating with the hand’s capacity for spatial acuity. Deeper within the palmar tissue are Pacinian corpuscles, which respond to high-frequency vibration and deep pressure. The dorsal skin has a much lower density of these fine mechanoreceptors, focusing instead on general sensations like pain, temperature changes, and broad mechanical contact.