The dermis, the middle layer of your skin, contains a dense collection of structures that support nearly every function skin performs: sensation, temperature control, oil and sweat production, and structural support. It sits between the outer epidermis and the deeper hypodermis, ranging from just 0.6 millimeters thick over the eyelids to 4 millimeters thick on the back. Within that thin space, you’ll find blood vessels, nerve endings, glands, hair follicles, muscles, lymphatic vessels, and several types of connective tissue and cells.
Two Layers of Connective Tissue
The dermis is organized into two layers that merge together without a sharp boundary. The upper layer, called the papillary dermis, is thinner and made of loose connective tissue. It sits directly against the epidermis and forms finger-like projections that interlock with it, increasing the contact area between the two layers. The lower layer, called the reticular dermis, is thicker, denser, and less cellular. It provides most of the skin’s mechanical strength.
These two layers differ at the cellular level. Fibroblasts in the papillary layer produce different types of protein than those in the reticular layer. Papillary fibroblasts generate proteins that contribute to scar-free wound healing, while reticular fibroblasts produce the thick, fibrous collagen bundles (types I and III) responsible for the skin’s toughness. This distinction helps explain why deep wounds that damage the reticular layer are more likely to scar.
Collagen and Elastic Fibers
Collagen is the principal component of the dermis, with types I and III making up the bulk of it. These fibers give skin its tensile strength, the quality that keeps it from tearing under tension. The collagen fibers in the reticular layer are bundled into thick, interwoven networks, while those in the papillary layer are finer and more loosely arranged.
Elastic fibers, made of a stretchy protein called elastin, make up less than 1% of the dermis by weight but play an outsized role. They allow skin to snap back into shape after being stretched or compressed. Without them, skin would stay deformed every time you smiled, pinched, or pressed on it. Both collagen and elastic fibers sit within a gel-like substance made up of large sugar-protein molecules, including hyaluronic acid, which holds water and keeps the tissue hydrated and cushioned.
Collagen production drops significantly with age. In sun-protected skin, people over 80 produce roughly 75% less collagen than adults in their late teens and twenties. This gradual loss is one of the main reasons skin thins, sags, and wrinkles over time.
Sensory Nerve Endings
The dermis is packed with specialized nerve endings that detect touch, pressure, vibration, temperature, and pain. Four types of touch receptors (mechanoreceptors) are scattered through the skin at different depths, each tuned to a different type of sensation.
- Meissner’s corpuscles sit in the upper dermis, especially in the fingertips, palms, and soles. They detect light touch and movement across the skin, which is why your fingers are so sensitive when handling objects.
- Merkel’s discs are found near the junction of the epidermis and dermis, concentrated in the fingertips, lips, and genitalia. They respond to sustained pressure and help you detect shapes and textures.
- Ruffini endings are located deep in the dermis and in nearby tendons and ligaments. They sense skin stretching and help your brain track finger position. They account for about 20% of the receptors in the hand.
- Pacinian corpuscles are large, onion-shaped receptors found in the deeper dermis and subcutaneous tissue. They detect vibration and fine texture, responding to rapid changes in pressure rather than sustained contact.
Beyond these touch receptors, the dermis also contains free nerve endings that detect temperature changes and pain. Together, these sensory structures create the detailed tactile map your brain uses to interact with the world.
Blood Vessels
The dermis contains an elaborate network of blood vessels arranged in two horizontal layers. The deeper layer runs along the boundary between the dermis and the hypodermis. The shallower layer, called the subpapillary plexus, sits just below the epidermis and is made up mostly of tiny capillaries and small veins. These two layers are connected by vertical vessels that carry blood between them.
This vascular network serves two critical functions. First, it delivers oxygen and nutrients to the epidermis, which has no blood supply of its own and depends entirely on diffusion from dermal capillaries. Second, it plays a major role in temperature regulation. When you’re hot, blood vessels near the surface dilate to release heat. When you’re cold, they constrict to conserve it. The dermis also contains arteriovenous shunts, specialized connections that let blood bypass the capillary beds entirely and flow directly from arteries to veins. These shunts are key players in rapid thermoregulation.
Lymphatic Vessels
Running alongside the blood vessels is a network of lymphatic capillaries. These thin-walled vessels collect excess fluid, proteins, and waste products from the tissue and funnel them toward lymph nodes for filtering. The walls of dermal lymphatic capillaries are closely connected to the surrounding connective tissue, which allows them to respond directly to pressure changes in the tissue. Tiny one-way valves inside the capillaries keep fluid moving in one direction, toward the center of the body. When this valve system fails, fluid accumulates in the skin and causes swelling known as lymphedema.
Sweat and Oil Glands
Three types of glands are embedded in the dermis, each producing a different secretion.
Eccrine sweat glands are coiled, tube-shaped glands distributed across nearly the entire body. Their secretory portions sit in the lower dermis and upper hypodermis, and their ducts spiral upward through the epidermis to open as pores on the skin surface. They produce a watery sweat made of electrolytes and water, and they release it without destroying any cells in the process. Eccrine glands are the body’s primary cooling system.
Apocrine sweat glands are larger and less coiled. They’re found only in specific areas: the armpits, around the nipples, near the anus, and in the genital region. Their ducts empty into hair follicles rather than directly onto the skin surface. The fluid they produce is thicker and contains proteins and lipids. It’s initially odorless, but bacteria on the skin surface break it down into the compounds responsible for body odor.
Sebaceous glands are pear-shaped oil glands attached to hair follicles. They’re found everywhere on the body except the palms, soles, lips, and tops of the feet. These glands produce sebum, an oily substance that lubricates and waterproofs both hair and skin. Their secretory method is extreme: the entire cell fills with oil, ruptures, and dies, releasing its contents into the hair follicle canal. The face tends to have especially large and active sebaceous glands, which is why it’s a common site for oily skin and acne.
Hair Follicles and Arrector Pili Muscles
Hair follicles are tube-shaped structures that extend from the skin surface down into the dermis or even the hypodermis. Each follicle is part of a structural unit that also includes a sebaceous gland and a small smooth muscle called the arrector pili muscle. This muscle runs at an angle from the follicle to the upper papillary dermis. When it contracts, it pulls the hair upright, creating what you recognize as goosebumps. That contraction also squeezes the attached sebaceous gland, helping push sebum onto the skin surface.
The follicle’s bulge region, where the arrector pili muscle attaches, is also a reservoir of stem cells. These cells can regenerate not only the hair follicle itself but also contribute to skin repair after injury.
Resident Cells of the Dermis
Several cell types live permanently in the dermis. Fibroblasts are the most abundant and the most important for structural maintenance. They produce collagen, elastin, and the gel-like ground substance that fills the spaces between fibers. The dermis also contains mast cells, which store granules of histamine and other chemicals involved in allergic reactions and inflammation. When you develop a hive or a mosquito bite swells, mast cells in the dermis are largely responsible. Macrophages patrol the tissue, engulfing debris, dead cells, and invading microorganisms. Together, these immune cells form an active defense layer just beneath the skin surface.