Skin has three layers: the epidermis on top, the dermis in the middle and the hypodermis underneath. This interactive 3D model shows them as a cut-open block you can turn, with the five layers of the epidermis, hair follicles, sweat glands, nerves and blood vessels inside. Click any part to open its card, or switch to thick skin to compare it with the thin skin that covers most of the body.
The 3 layers of skin
The three layers of the skin are the epidermis, the dermis and the hypodermis. The skin is the body’s largest organ. In an adult it makes up about 16 percent of body weight and covers 1.5 to 2 square meters.
The epidermis is the outer layer. It is only 0.05 mm thick on the eyelids and up to 1.5 mm thick on the palms and soles. It has no blood vessels. It forms a waterproof barrier and makes melanin, the pigment that shields skin from UV light.
The dermis is the middle layer, 1.5 to 4 mm thick. It makes up about 90 percent of the thickness of skin. It is strong connective tissue that holds blood vessels, nerves, hair follicles and glands.
The hypodermis is the deepest layer. It is loose connective tissue and fat, and it is also called the subcutaneous layer. Its thickness varies across the body and from person to person.
The 5 layers of the epidermis
The five layers of the epidermis, from deepest to the surface, are the stratum basale, stratum spinosum, stratum granulosum, stratum lucidum and stratum corneum. Thin skin has only four of them, because the stratum lucidum is found only in thick skin. Click a layer name to see it in the epidermis close-up.
| Layer | What the cells look like | What it does |
|---|---|---|
| Stratum basale | One row of stem cells, with melanocytes and Merkel cells among them | Divides to make every new keratinocyte |
| Stratum spinosum | Eight to 10 layers of keratinocytes, with Langerhans cells | Starts making keratin and a water-repelling fat |
| Stratum granulosum | Three to five layers of flattening cells full of granules | Turns cells into tough, keratin-filled scales |
| Stratum lucidum | A thin clear band of flat, dead cells (thick skin only) | Adds depth on the palms and soles |
| Stratum corneum | 15 to 30 layers of flat, dead cells | Forms the waterproof outer barrier |
Keratinocytes, the main skin cells, are born in the stratum basale and rise through the layers. On the way up they flatten, fill with keratin, a tough protein, and die. The dead cells flake off the surface, and the whole stratum corneum is replaced in about 4 weeks. Press Skin renewal to watch it happen. Until they die, keratinocytes have the same parts as any animal cell, which you can explore in the cell 3D model.
Three other cell types sit among the keratinocytes. Melanocytes make melanin, which comes in two forms: eumelanin, which is black or brown, and pheomelanin, which is red. Langerhans cells are immune cells that engulf bacteria and damaged cells. Merkel cells are touch receptors that connect to sensory nerves. Skin color depends on melanin, carotene and hemoglobin. Melanin production peaks about 10 days after first sun exposure, so a tan builds slowly. See it with the Sun action.
What is in the dermis
The dermis holds the structures that make skin work: collagen fibers, blood vessels, nerves, hair follicles and glands. It has two parts. The papillary dermis is the thin top part, and the reticular dermis below it is about three times thicker.
The papillary dermis pushes up into the epidermis in finger-like folds called dermal papillae. Fingerprints form where the stratum basale meets the papillae. The reticular dermis is dense and packed with bundles of collagen, which gives skin strength, and elastin, which lets it stretch. Fibroblasts make both fibers.
The dermis also holds the hair and the glands:
- A hair follicle is the tube that holds a hair root. The root ends in the hair bulb, where new cells build the hair shaft, the part you see.
- The arrector pili is a tiny smooth muscle on each root. When it contracts, the hair stands up and the skin forms goosebumps. Slide the temperature to cold, or press Cold, to watch it. Smooth muscle is one of the types covered in examples of muscle tissue.
- Sebaceous glands are oil glands. Most attach to hair follicles and make sebum, an oily mix of lipids that waterproofs skin and hair.
- Sweat glands are coiled tubes. A sweat duct carries sweat up to a pore on the surface. An average person has about 3 million of them. Eccrine glands are found across the skin and make watery sweat. Apocrine glands are larger, usually open into hair follicles and make a thicker sweat. In heat, an active person can lose 0.7 to 1.5 L of sweat per hour. Try the Hot action.
Blood and nerves run through the dermis. Arteries and veins run in the hypodermis and send smaller vessels up, and capillaries fill the papillary layer. In heat the small arteries widen and release heat. In cold they narrow to save it. For more on vessels, see examples of blood vessels.
Nerves in the dermis carry signals from touch, pain and temperature sensors to the brain. Free nerve endings sense pain and temperature. Meissner corpuscles sit in the papillae and detect light touch. Pacinian corpuscles are larger, up to 5 mm long and 3 mm wide, sit deeper and respond to vibration. Press Touch and tap the skin to light them. The nervous tissue article explains how the signals travel.
The hypodermis and adipose tissue
The hypodermis is the layer of loose connective tissue and adipose tissue, which is body fat, below the dermis. Adipose tissue is made of cells called adipocytes that store fat.
The stored fat does three jobs: it is an energy store, it cushions the body and it insulates against cold. Hormones and genes decide where the body stores it. The hypodermis is well supplied with blood, and arteries and veins run through it. A small number of adipocytes also appear in the papillary dermis above.
Thin skin vs thick skin
Thick skin covers only the palms and soles, and thin skin covers the rest of the body. The main difference is the epidermis: thick skin has five layers and thin skin has four. Use the pill at the top of the model to switch between thin skin and thick skin.
| Feature | Thin skin | Thick skin |
|---|---|---|
| Where | Most of the body | Palms and soles |
| Epidermis layers | Four | Five |
| Epidermis thickness | Down to 0.05 mm on the eyelids | Up to 1.5 mm |
| Stratum corneum | Thinner | About five times thicker |
| Stratum lucidum | Absent | Present |
| Hair follicles and oil glands | Present | Absent |
| Eccrine sweat glands | Present | Highest concentrations |
| Meissner corpuscles | Fewer | Concentrated in fingertips, palms and soles |
The thick skin of the fingertips carries the ridges of the fingerprints, which follow the dermal papillae below.
Skin and the integumentary system
The integumentary system is the skin and its accessory structures, which are the hair, nails and glands. It is the largest organ system in the body. It does five jobs:
- Protection. The epidermis blocks water loss and germs, melanin guards against UV damage and sweat contains dermcidin, a natural antibiotic.
- Sensation. Touch, pressure, pain and temperature receptors report to the brain. Touch receptors are most concentrated in the fingertips.
- Temperature control. Sweat cools the body as it evaporates, and the blood vessels of the dermis widen or narrow to release or save heat.
- Vitamin D. The epidermis makes vitamin D when it is exposed to UV light.
- Insulation and cushioning. The fat of the hypodermis pads the body and holds heat.
An integumentary system diagram usually shows a cross section with the three layers, a hair follicle, glands and receptors. This model is the same diagram in 3D, and you can pull the layers apart on the View tab. The skin is one of the body’s many organs; examples of organs lists the others. Melanin protects the DNA inside skin cells from UV damage, and the DNA 3D model shows that molecule up close.
How to use the model
The model opens on thin skin with the front cut away. Drag to rotate, scroll to zoom and click any part to open its card. The camera flies to the part and the rest of the block fades back.
- The Parts tab lists every part by group and has the switch that turns labels on. Hover a name to light it up in the block.
- The View tab sets how the block is cut, pulls the layers apart and shows only the part you picked.
- The In action tab runs the five scenes: cold, hot, sun, skin renewal and touch.
- The epidermis is too thin to read at block scale, so the cells and the five strata open in a close-up. Use the Back to whole skin button to leave it.
The model is not to scale. The epidermis is drawn thicker than life so you can see its layers. On the eyelids the real epidermis is 0.05 mm thick. The block is a simplified piece of skin about 3 mm wide, and the number of hairs and glands is lower than in real skin.
Frequently asked questions
How many layers of skin are there?
Skin has three layers: the epidermis, the dermis and the hypodermis. The epidermis is the outer layer, the dermis is the thick middle layer and the hypodermis is the fat layer underneath. The epidermis itself has four or five sub-layers called strata.
What are the 5 layers of the epidermis?
From deepest to the surface, the five layers are the stratum basale, stratum spinosum, stratum granulosum, stratum lucidum and stratum corneum. The stratum lucidum is found only in thick skin on the palms and soles. Thin skin has the other four.
What is the largest organ in the body?
The skin is the largest organ in the body. In an adult it makes up about 16 percent of body weight and covers 1.5 to 2 square meters. With the hair, nails and glands, it forms the integumentary system.
What causes goosebumps?
Goosebumps are caused by the arrector pili, tiny muscles that pull each hair upright. Nerves of the sympathetic nervous system trigger the contraction, most often in the cold. The raised hair traps a layer of air that insulates, and in humans it leaves a visible bump. Press Cold in the model to see it.
What gives skin its color?
Skin color comes from three pigments: melanin, carotene and hemoglobin. Melanin matters most. Melanocytes in the stratum basale make it in two forms, eumelanin (black or brown) and pheomelanin (red).
How often does skin replace itself?
The surface layer of the epidermis is replaced about every 4 weeks. Cell turnover takes 28 to 30 days in young adults and 45 to 50 days in older adults. New cells form in the stratum basale and push up toward the surface.
What is the difference between thick and thin skin?
Thick skin covers the palms and soles and has five epidermal layers, while thin skin covers the rest of the body and has four. Thick skin has a clear stratum lucidum and a much thicker stratum corneum. It also has the highest concentrations of eccrine sweat glands. Switch the model to thick skin to compare.
Which skin layers do first-, second- and third-degree burns reach?
A first-degree burn reaches only the epidermis, and it usually heals in a few days. A second-degree burn reaches the epidermis and part of the dermis, and it blisters. A third-degree burn goes through the epidermis and dermis, destroys tissue and damages nerve endings, so it may hurt less. Third-degree burns need medical attention.
What are dermal papillae, and do they make fingerprints?
Dermal papillae are finger-like folds of the papillary dermis that push up into the epidermis and anchor it. Fingerprints form in the fetus where the stratum basale meets the papillae. The pattern does not change as you grow or age.
What is the difference between sweat glands and oil glands?
Sweat glands make watery sweat that cools the body, while sebaceous glands, the oil glands, make sebum, an oily mix of lipids that waterproofs skin and hair. Sweat glands are coiled tubes that open at pores or hair follicles. Most sebaceous glands attach to hair follicles, and many do not become active until puberty.
Credits and sources
- Facts on the part cards: OpenStax Anatomy and Physiology 2e, Chapter 5 introduction; OpenStax Anatomy and Physiology 2e, 5.1 Layers of the Skin; OpenStax Anatomy and Physiology 2e, 5.3 Functions of the Integumentary System; NCI SEER Training, Layers of the Skin; Cleveland Clinic, Skin; OpenStax Anatomy and Physiology 2e, 5.4 Diseases, Disorders and Injuries of the Integumentary System; The Human Cutaneous Sensory Corpuscles: An Update (PMC7827880); OpenStax Anatomy and Physiology 2e, 5.2 Accessory Structures of the Skin.
- The 3D model, labels and poster image are by 33Science, licensed CC BY 4.0. Credit 33Science and link to this page.