Human skin has three main layers: the epidermis, the dermis, and the hypodermis. Each layer has a distinct structure and job, and together they range from about 0.5 mm thick on the eyelids to 4.0 mm thick on the heels of your feet. Understanding what each layer does helps explain everything from why a scrape bleeds (or doesn’t) to how your body regulates temperature.
Epidermis: The Outer Layer
The epidermis is the layer you can see and touch. It’s made primarily of a tough protein called keratin, which forms a waterproof shield that keeps bacteria, germs, and environmental elements like rain and UV light from getting inside your body. The epidermis also houses immune cells called Langerhans cells that help detect and fight invaders.
One important detail: the epidermis contains no blood vessels. It gets all of its nutrients from the dermis below. That’s why a shallow scrape that only damages the epidermis may sting but won’t bleed.
Your epidermis constantly renews itself. New skin cells form at the bottom of the layer and gradually push upward as they mature. By the time they reach the surface, they’re flat, dead, and ready to shed. Your body loses roughly 40,000 old skin cells every day, and you get an entirely new outer surface about every 30 days.
The Five Sublayers of the Epidermis
The epidermis itself is divided into five thinner strata, listed from deepest to most superficial:
- Basal layer (stratum germinativum): The innermost layer where new skin cells are born. It also contains melanocytes, the cells that produce pigment and determine skin color, along with Merkel cells that help you sense light touch.
- Squamous cell layer (stratum spinosum): Maturing cells, now called keratinocytes, are pushed into this layer. Langerhans immune cells live here.
- Stratum granulosum: Keratinocytes continue to flatten and harden as they move upward, forming the waterproof barrier.
- Stratum lucidum: A thin, translucent layer found only in thick skin areas like the palms and soles.
- Stratum corneum: The outermost layer, made of 10 to 30 thin sheets of dead, flattened keratinocytes that continuously shed and are replaced from below.
Dermis: The Middle Layer
Beneath the epidermis sits the dermis, a much thicker layer that gives skin its strength, elasticity, and blood supply. This is where you’ll find blood vessels, sweat glands, hair follicles, nerve endings, and a dense network of collagen and elastin fibers that let your skin stretch and snap back into shape. The dermis has two sublayers of its own.
Papillary Dermis
The papillary dermis is the thinner, upper portion. It contains fine collagen fibers, capillaries that feed the epidermis above, and touch receptors called Meissner corpuscles that detect light pressure and texture. When you run your fingertips across fabric and feel the weave, those receptors are doing the work.
Reticular Dermis
The reticular dermis is the thicker, lower portion. It holds a dense mesh of collagen and elastin fibers that provide structural support, along with larger blood vessels, lymphatic channels, hair follicles, and sweat glands. Deeper pressure sensors called Pacinian corpuscles and stretch sensors called Ruffini corpuscles also reside here and in the tissue below, picking up vibration and sustained pressure.
Because the dermis is rich in blood vessels, any cut deep enough to reach it will bleed. Sweat glands in the dermis also play a key role in cooling you down: they push sweat to the skin’s surface through pores, and as it evaporates, your body temperature drops.
Hypodermis: The Deepest Layer
The hypodermis, also called subcutaneous tissue, is the fatty layer beneath the dermis. It’s composed mainly of adipose (fat) tissue and connective tissue. Some sources don’t count the hypodermis as a true “layer of skin” since it sits below the dermis, but it’s so functionally connected to the skin above that it’s almost always discussed alongside the epidermis and dermis.
This layer serves three main purposes. First, it acts as a cushion, absorbing impacts and protecting the muscles and bones underneath when you fall or bump into something. Second, it stores energy in the form of fat cells called adipocytes, which your body can draw on when needed. Third, it insulates you against cold by trapping body heat. The hypodermis also anchors your skin to the muscles and bones below it through bands of connective tissue, which is why skin moves with your body rather than sliding freely over it.
How Burns Relate to Skin Layers
One practical way to understand these layers is through burn classification. A superficial burn damages only the epidermis, causing redness and pain but no blistering. A partial-thickness burn extends into the dermis, producing blisters and more intense pain because nerve endings in the dermis are exposed. A full-thickness burn destroys both the epidermis and the entire dermis, often reaching the hypodermis. These burns can actually be less painful initially because the nerve endings themselves have been destroyed, though the damage is far more serious and typically requires surgical treatment.
How the Layers Work Together
The three layers function as a coordinated system rather than independent sheets. The dermis sends blood and nutrients upward to keep the epidermis alive, since the epidermis has no blood supply of its own. The epidermis, in turn, forms the barrier that protects the delicate structures in the dermis from infection and UV damage. Meanwhile, the hypodermis anchors everything in place and provides insulation and shock absorption that neither upper layer could manage alone. Melanocytes in the deepest part of the epidermis produce pigment that absorbs UV radiation before it can reach the DNA-rich dividing cells below, and immune cells scattered across both the epidermis and dermis mount a defense if anything breaches the surface.
Your skin is the largest organ in the body, and its layered architecture is what makes it so versatile. The same organ that keeps water out also lets you feel the lightest touch, regulates your temperature, stores energy, and fights off infection.