Table of ContentsView AllTable of ContentsAnatomyFunctionAssociated ConditionsTests
Table of ContentsView All
View All
Table of Contents
Anatomy
Function
Associated Conditions
Tests
The skin is the largest organ of the human body. Its main functions are protection, thermal regulation, and sensation. The skin is made up of three main layers: theepidermis, thedermis, and thesubcutaneous layer.
Verywell / Alexandra Gordon
The skin is part of theintegumentary system, which also includes the nails, hair, and exocrine glands. It is an incredibly large organ, accounting for 15% of an adult’s total body weight.
Total skin thickness varies depending on where it is found on the body. The thickest skin is found on the back, the palms of the hands, and the bottoms of the feet, where it can be up to 3 millimeters (mm) thick.The thinnest skin is found on the eyelid, where the epidermis measures just 0.05 mm with very little dermis and subcutaneous fat.
The three major layers of the skin each contain specialized cells, tissues, and appendages, and each performs unique functions for the body.
Epidermis
The epidermis is the outermost layer of the skin, the layer of skin which is visible. The epidermis is also the thinnest of the three skin layers. It is an avascular skin layer, so it does not contain blood vessels.
This tough layer is chiefly made up of keratin and epithelial cells, stacked in tightly-packed sheets. It is in a state of constant renewal, as new skin cells are continuously created while older cells are sloughed away in a process called desquamation.
Important cell types of the epidermis include:
The epidermis itself is made up of four layers, with some areas having a specialized fifth epidermal layer.
Keratinocytes go through radical changes as they travel from the deepest layer of the epidermis where they are “born,” to the top layer where they eventually slough away. The entire cell turnover process from cell birth to sloughing away takes, on average, about 28 days to complete.
Stratumis a term that means a sheet-like layer.
The four layers of the epidermis are:
Dermis
The dermis is the middle layer of the skin. The dermis is the layer that gives skin it’s structure and elasticity.
The dermis has two layers: the papillary layer and the reticular layer.
The reticular layeris the thicker of the two dermal layers. It is primarily made up of fibers of collagen and elastin. This gives the dermis strength and allows it to stretch.
Within the reticular layer of the dermis are found:
Subcutaneous Layer
The upper two layers of the skin sit atop the subcutaneous tissue. This layer is sometimes called the hypodermis or panniculus.
This layer is primarily made up of fatty tissue called adipose tissue. This is where the body reserves its fat stores.
The subcutaneous layer is also made up of loose connective tissue, larger blood vessels, and nerves. This layer helps connects the upper skin to the musculature below.
This layer varies in thickness depending on where it’s found on the body (it’s thickest on the buttocks, palms, and feet) as well as age, sex, and health of an individual.
Anatomical Variations
There is some indication that men, biologically, have overall thicker skin than women.Some studies, though, have found no significant difference between the thickness of male versus female skin.
The skin carries out several critical functions.
Protection
The main purpose of the skin is to serve as an organ of protection—frominjury, infection, UV radiation, and moisture loss.
The skin creates a type of armor, a physical barrier to prevent pathogens from entering the body. In addition, sebum is slightly acidic, creating an environment that isn’t ideal for harmful microbes.
The subcutaneous layer specifically acts as a cushion to protect the more delicate bones and musculature beneath.
The skin also protects the body from UV rays. As mentioned before, melanin acts as a type of shield, blocking UV light so it cannot penetrate farther than the upper skin tissues. Sun exposure triggers the melanocytes to create more melanin, as the skin tries to protect itself from further damage (in other words, the skin tries to create a stronger shield). The creation of melanin is what causes the skin to tan, and is an indication of sun damage.
The skin is also key to preventing excess water loss. The epidermis creates a barrier that helps slow down the evaporation of water, as well as prevents excess water from being absorbed into the skin while bathing or swimming.
Sensation
The plethora of nerve endings found in the skin allows the human body to detect sensations of pressure, temperature, and pain. Sensory receptors are found throughout the skin, are especially numerous throughout the dermis.
Thermoregulation
The skin helps to maintain the body temperature within a very specific range.
When the body is getting too cool (hypothermia) the arrector pili muscles cause the hair to stand up, giving you goosebumps. The thin layer of air trapped between the hair and the body acts as an insulator helping to warm the body.
The blood vessels within the dermis also constrict, a process called vasoconstriction. Constricting the vessels at the skin’s surface allows the skin to cool while maintaining the warmed blood for the body’s core and critical organs.
When the body is becoming too warm, the sudoriferous glands release sweat. As the sweat evaporates, it cools the skin.
Synthesis of Vitamin D
The amount of sun needed to get an adequate amount of vitamin D varies widely and is dependant on a host of different factors including skin tone, season, location (near the equator versus northern latitudes), time of day, and the amount of skin that is exposed. It’s suggested you follow your healthcare provider’s recommendation for the right amount of sun exposure for you.
Vitamin D supplementsare also an option.
There are hundreds of conditions that affect the skin, and they have a wide range of causes.
Benign Skin Lesions
Inflammatory Rashes/Conditions
There is a vast array of inflammatory conditions that can affect the skin. Some are temporary, while others are chronic. Some may require treatment while others will heal on their own. They often resemble one another, so it’s always a good idea to get a diagnosis from a healthcare provider.
Injuries
Cutaneous Infections
Viral Infections
Many conditions that don’t originate in the skin can cause cutaneous symptoms. They include:
Pigmentation Disorders
These are disorders that affect the way the skin produces melanin. Pigmentation conditions can either cause an increase in color (hyperpigmentation) or a loss of color (hypopigmentation). Some pigmentation conditions are treatable while others are not.
Cancer
Skin canceris most often linked to excessive sun exposure. Most forms of skin cancer are highly treatable, but early detection is key.
There are three types of skin cancer:
Genetic Conditions
Certain genetic conditions can cause the skin to not function as it should. Most are fairly rare. They include:
There are several tests that are performed on the skin to help diagnose various conditions that can affect this organ.
Biopsy
A skin biopsy is a procedure in which cells or skin tissue is removed for examination under a microscope. A biopsy is used to check for skin cancer, infection, and to help identify certain rashes.
There are three main techniques used to do a skin biopsy: punch, shave, and excision.
You will be given a local anesthetic prior to the biopsy. Stitches may be used to close the biopsy site in some cases.
Types of Skin Cancer Biopsy
Patch Test
Patch testsare common done to help identify possible causes of contact dermatitis. Adhesive patches with small pads impregnated with common allergens are placed on the back and left for a period of 48 hours. After the patches are removed, the skin is checked for signs of irritation, redness, or swelling. This allows one to know the substances that trigger contact dermatitis.
Woods Lamp Examination
A Woods lamp is a type of black light that allows a medical professional to detect things that aren’t easily seen with the naked eye.
During an exam, you will sit in a dark room. The healthcare provider holds a Woods lamp close to your skin to look for color changes. The presence of certain fungi or bacteria will appear in particular colors. The borders of hyperpigmentation or hypopigmentation are more easily seen under a Woods lamp as well.
Skin Prick Test
Theskin prick testis a test that is performed on the skin, but isn’t used to diagnose a skin condition. Instead, skin prick tests are used to determine which substances a person may be allergic to. This includes things that cause allergic rhinitis and food allergies.
Skin prick tests are typically done on the back or on the arm. A device with small points, which have been dipped in allergen extracts, is used to prick or scratch the skin’s surface. After 15 to 20 minutes, the skin is examined. Any inflamed bumps or wheals indicated a positive reaction.
A Word From Verywell
For an organ that is so visible and familiar, the skin is surprisingly complex. As the largest organ of the human body, the skin is responsible for many important functions. There are hundreds of conditions that can affect the skin; many of them look incredibly similar and are difficult to distinguish one from another. If needed, see a healthcare provider for help in diagnosing and treating your skin condition.
7 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Habif TP.Clinical Dermatology E-Book. 5th ed. Elsevier Health Sciences; 2009.
Dutton J, Gayre G, Proia A.Diagnostic Atlas of Common Eyelid Diseases. New York: Taylor & Francis Ltd.; 2007:1. doi:10.3109/9781420016321
Alberts B, Johnson A, Lewis J, Raff M, Roberts K, Walter P.Molecular Biology of the Cell, 4th ed. New York: Garland Science; 2002.
Kakasheva-Mazhenkovska L, Milenkova L, Gjokik G, Janevska V.Variations of the histomorphological characteristics of human skin of different body regions in subjects of different age. Prilozi. 2011;32(2):119-28.
Rahrovan S, Fanian F, Mehryan P, Humbert P, Firooz A.Male versus female skin: What dermatologists and cosmeticians should know.Int J Womens Dermatol. 2018 Jun 22;4(3):122-130. doi:10.1016/j.ijwd.2018.03.002
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