The skin is the largest organ of the body. Read about the three layers of skin, the function of the skin and common diseases!


The skin (Cutis) is a vital organ that covers the entire outer surface of our body. It is stretchy and elastic, distinguishes the organism against the outside world and protects it from dehydration and from harmful influences such as pathogens and sunlight. Read everything important about the layers of the skin, their functions and important diseases of the cutis!

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  • What is the skin?

  • What is the function of the skin?

  • Where is the skin?

  • What problems can the skin cause?

What is the skin?

The skin (cutis) is a surface organ, the largest single organ of the body. As a protective shell of our body, it covers an area of ​​one and a half to two square meters in a mid-sized adult human being. With a thickness of one to two millimeters, the skin organ weighs about three and a half to ten kilograms. Their color changes from person to person - it depends on the amount of blood, the pigment content and the thickness of the epidermis (top layer of the cutis).

How many skin layers does a human have?

The structure of the skin comprises three layers. From outside to inside these are:

  • Epidermis (epidermis)
  • Dermis or corium (dermis)
  • Subcutis


The epidermis consists for the most part of a layer of horns, which peels off to the outside and constantly renewed from below. Read more in the article Epidermis.

Dermis (dermis, corium)

The dermis is the middle of the three layers of skin. It consists of tight connective tissue and contains, among other things, sebaceous glands. Read more about the dermis in the contribution Dermis.


The subcutis consists of loose connective tissue with more or less embedded fatty tissue. You can read more about this in Subcutis.

Skin appendages

Skin appendages include hair, nails and glands such as sweat and sebaceous glands. Read more about the latter in the article Sebum glands.

What is the function of the skin?

The function of the skin is primarily to give the body protection. Just how vital the Cutis is can be seen when large areas have been destroyed, for example, by incineration. Even a loss of 20 percent of the skin can be deadly. In addition to the protective function, the Cutis also fulfills other tasks, such as a sensory organ.

Protective function of the skin to the outside

The outer horny layer (part of the epidermis), which is saturated with fatty substances, protects the organism on the one hand against excessive loss of water through evaporation. On the other hand, intact skin prevents the ingress of pathogens and harmful substances such as chemicals. To a certain extent, it also provides mechanical protection of internal structures and organs, for example from knocks or bumps.

The function of the skin is also to reflect and absorb sunlight through the horny layer and skin surface film. Deep penetrating rays are almost 100 percent absorbed and converted into heat by the melanin pigment, a black-brown to reddish dye.

The perspiration from the sweat glands and the sebum from the sebaceous glands together form the so-called acid mantle of the skin. Its low (acidic) pH has an antimicrobial effect: it inhibits the growth of many bacteria and fungi on the cutis.

Protective function inside

The inward protective function of the cutis consists of antibody formation. When the body's own immune system is mobilized by the Langerhans cells of the epidermis, the body pumps blood and lymph into the affected skin region. The consequences are redness, swelling and wheals. Rashes in infectious diseases such as rubella, measles, scarlet fever and vaccine reactions are the result of this immunological defense reaction.

heat control

A contraction (contraction) of the cutaneous vessels prevents excessive heat release. The same purpose is the "goose bumps": It is caused by contraction of Haarbalgmuskeln hairy body parts. As a result, the cutis forms small elevations, and the fine hairs straighten up. This reduces the heat output.

By expanding the vessels, however, a heat release is promoted, thus preventing heat build-up in the body.

The release and evaporation of the sweat serves to regulate the heat.

Sensory perception

The sensory organ skin registers stimuli such as pressure, temperature and pain through specific receptors. This is also referred to as surface sensitivity. Read more in the article Tactile Perception.

Other tasks of the skin

The Cutis fulfills even more functions. For example, to a small extent, substances that are otherwise excreted only via the kidneys (urinary substances) are secreted by sweat glands (such as saline). In addition, the formation of vitamin D takes place in the epidermis under the influence of sunlight (more precisely, UV-B light).Its main function is the regulation of the calcium and phosphate balance. Both minerals are important for building bones and teeth.

How is the skin changed in atopic dermatitis patients? Is the skin disease inherited? And does it have anything to do with the immune system?

Where is the skin?

The cutis covers the entire body surface. At the body openings (mouth, nose, genital area) it passes into the mucous membrane.

Regardless of the three-layer structure of the skin, it is possible to differentiate between two different appearances of the cutis on the body:

Thus, the skin on the soles of the feet, the palms and the inner sides of the fingers run in fine grooves, which are arranged in parallel - like fine strips. This structure serves to make the cutis rough and grippy, to give it a hold. Doctors speak here of the so-called groin. It accounts for about four percent of the body surface.

The skin on the rest of the body (about 96 percent of the body surface) consists of rhombic to polygonal furrows, which are genetically fixed in their shape and run in characteristic lines. Hair grows out of the furrows of this field, sweat glands open outward through the excretory ducts.

What problems can the skin cause?

The cutis can cause numerous problems, such as abscesses (capsule-packed pus), boils (purulent inflammation of hair follicles) or herpes infections (such as cold sores, shingles).

Atopic dermatitis (eczema) is a genetic chronic skin condition that is accompanied by inflammatory changes in the cutis and itching. It runs in batches and can be "triggered" by so-called provocation factors. These include, for example, frequent washing, heavy sweating, pollen, pet dander, infections and stress.

Psoriasis is a chronic inflammatory skin disease that causes scaly, itchy changes in the cutis. Especially affected are knees, elbows and scalp. Some patients may also have their joints or nails affected.

In a contact dermatitis (also called allergic contact dermatitis), the skin is hypersensitive to contact with certain substances such as fragrances or nickel. Typical symptoms include redness and severe itching.

In defensive weakness, it can lead to a fungal disease of the skin (dermatomycosis).

Warts (Verrucae) are small, sharply limited growths of the epidermis. They are generally benign. The cause of warts are human papillomaviruses (HPV). There are different types of warts such as "common" warts (especially on hands and feet) or plantar warts (almost only on the soles of the feet).

A birthmark (pigment nevus) is caused by an increase of pigment-forming cells (melanocytes) in the epidermis. It is colloquially referred to as a liver spot. The predisposition for moles is genetically determined. Their expression is significantly influenced by the sunlight. For example, moles develop primarily on body parts that are exposed to the sun.

Excessive exposure to the sun can cause sunburn - burning of the cutis by UV light. Some medications can increase the risk of sunburn by making the cutis more sensitive to light. These include St. John's wort and certain antibiotics.

Frequent sunburns (especially in childhood) promote the development of skin cancer. The term refers to various malignant tumors of the cutis. The most important are basal cell carcinoma (basal cell carcinoma), squamous cell carcinoma (spiny cell carcinoma, spinalioma) and malignant melanoma.

A common disease of the skin In adolescents, acne (acne vulgaris) - a hormone-dependent disease of the sebaceous glands, which occurs especially in puberty.

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