Skin: Facts about the body’s largest organ and its functions

Pores and skin is the physique’s largest organ and, together with hair, nails, and skin-associated nerves and glands, is a part of the integumentary system, in keeping with the Nationwide Library of Drugs (opens in new tab) (NLM).

This method acts as a protecting barrier between the exterior setting and the within of the physique, shielding the inner organs in opposition to warmth, mild, harm and an infection. As well as, pores and skin performs an vital function in regulating physique temperature, stopping water loss, producing vitamin D and detecting sensations attributable to mechanical stimuli that make contact with or put stress on the pores and skin.

In a mean grownup, pores and skin accounts for about 15% of complete physique weight and covers a floor space of roughly 22 sq. ft (2 sq. meters), in keeping with the NLM (opens in new tab). There are completely different thicknesses and textures of pores and skin on completely different elements of the physique. For instance, pores and skin is thicker on the soles of the ft and palms of the palms, and thinner on the eyelids and genitals, the NLM (opens in new tab) states.

What number of layers does pores and skin have?

Labelled diagram of skin anatomy, showing the 3 layers of the skin described in the following paragraphs

The pores and skin has three layers, as depicted on this diagram of pores and skin anatomy. (Picture credit score: Flash Vector by way of Shutterstock)

Human pores and skin consists of three layers of tissue: the dermis, dermis and hypodermis. The thickness and density of pores and skin layers differ amongst people, relying on their age, intercourse and genetic components. For instance, feminine adults and kids usually have thinner pores and skin than male adults in most areas of the physique. Environmental influences, akin to publicity to solar or sure drugs, may have an effect on pores and skin density, NLM states.

Dermis

The dermis is the highest, seen layer of pores and skin. It’s additional divided into 4 layers: the stratum basale, stratum spinosum, stratum granulosum and stratum corneum. The thick pores and skin on the palms and soles of the ft has a further layer, referred to as the stratum lucidum, in keeping with the NLM.

Keratin, a protein made by cells within the dermis, provides pores and skin its toughness and power, in keeping with a 2009 evaluation revealed within the Journal of Anatomy (opens in new tab). The dermis is continually renewed as useless pores and skin cells are shed each day. New pores and skin cells type on the backside of the dermis. As these newer cells type, it takes them about one month to achieve the highest layer of the dermis. The new cells then substitute the previous cells on the pores and skin’s floor.

The dermis comprises melanocytes, that are cells that produce melanin, the pigment that provides pores and skin its colour. Melanin can also be accountable for suntans and freckles, in keeping with the NLM (opens in new tab).

Dermis

The dermis is the center layer of pores and skin, discovered beneath the dermis. It’s additional divided into two layers: the papillary dermis (the higher layer) and the reticular dermis (the decrease layer). The dermis is the thickest layer of pores and skin and comprises nerves and blood vessels. It’s also house to the sweat glands, oil glands and hair follicles. The dermis is made up largely of a protein referred to as collagen that makes pores and skin stretchy and robust, in keeping with the NLM (opens in new tab).

Hypodermis

The hypodermis, additionally referred to as subcutaneous fats, is the deepest layer of pores and skin. This layer is made up largely of fatty tissue, which helps to insulate the physique from warmth and chilly; cushion inner organs, muscle and bones; and shield the physique from accidents, in keeping with the NLM.

What’s the perform of the pores and skin?

Pores and skin capabilities as a protecting barrier in opposition to dangerous microbes, mechanical harm, warmth and dangerous substances that would in any other case harm the physique’s inner tissues. It additionally performs different vital roles within the physique, together with the next:

Sensing ache and contact: Nerve endings within the dermis include receptors that react to particular stimuli and set off indicators that get despatched to the mind, the place they’re interpreted as varied sensations, akin to ache, stress, contact, itchiness and temperature.
Producing sweat and oils: Sweat glands assist to chill the physique, and sebaceous glands make the oils that hold pores and skin comfortable and moist.
Rising hair: Hair follicles discovered within the dermis develop the hair in your head, face and physique. That hair additionally helps to regulate physique temperature and shield the physique from harm.
Bringing blood to the pores and skin: Blood vessels discovered within the dermis nourish the pores and skin and assist management physique temperature. When pores and skin turns into too scorching, blood vessels widen to launch warmth from the pores and skin’s floor, whereas chilly constricts blood vessels so they preserve physique warmth.
Preventing an infection: Lymphatic vessels, which drain fluid from the tissues and are an vital a part of the immune system, are housed within the dermis. They assist beat back infections and dangerous substances.
Producing vitamin D: Publicity to daylight triggers the manufacturing of vitamin D (opens in new tab) within the pores and skin.

Is pores and skin waterproof?

Top-down view of a dark-skinned child with curly hair sits near the pool and put their feet in the water.

Keratin is likely one of the principal elements of the pores and skin’s waterproof barrier. (Picture credit score: Maryna Terletska by way of Getty Photographs)

Pores and skin is waterproof because of the anatomical make-up of the higher and decrease layers of pores and skin. It’s a functioning organ that’s continually therapeutic and reworking, which helps preserve the pores and skin’s integrity, Dr. Ross Perry (opens in new tab), aesthetic physician and medical director at Cosmedics Pores and skin Clinics in England, advised Stay Science.

Keratin is likely one of the principal elements of the pores and skin’s waterproof barrier, in keeping with the NLM. As a result of this protein can’t dissolve in water — which means it is “water insoluble” — it seals the pores and skin barrier and prevents water from breaking by. Sebum, which can also be water insoluble, coats the floor of the pores and skin, defending it from drying out.

The group of fat within the superficial layers of the pores and skin may contribute to its waterproof properties, in keeping with a 2012 examine within the Journal of Investigative Dermatology (opens in new tab). The examine authors checked out samples of pores and skin scrapings and located fatty buildings “that had not beforehand been described in a organic system.” They not solely seem to make pores and skin immune to water but in addition allow the pores and skin to bend, the examine authors famous.

What’s the pores and skin microbiome?

vector illustration of the skin microbiome showing bacterial and fungal cells on the skin

A group of microbes, akin to micro organism and fungi, dwell on the pores and skin. (Picture credit score: Getty Photographs)

The pores and skin microbiome refers to microorganisms, akin to micro organism and fungi, that dwell on the floor of the pores and skin. These microbes are discovered totally on the superficial layers of pores and skin and hair follicles. Useful microbes discovered within the pores and skin microbiome play an vital function in defending the pores and skin from dangerous microbes which may overgrow on the pores and skin and trigger an infection, Perry advised Stay Science.

Many microbes on the pores and skin can produce molecules that stop the colonization of different microorganisms or alter their habits to make them much less threatening to the host. As well as, some micro organism, akin to Staphylococcus epidermidis, have been discovered to bolster resilience to infections by prompting the host’s immune system to supply extra messenger proteins important to combating irritation, in keeping with a 2018 evaluation revealed within the journal Nature Evaluations Microbiology (opens in new tab).

The pores and skin microbiome of a wholesome grownup stays comparatively secure over time, however the composition, or steadiness, of microbes might differ relying on the pores and skin web site. For instance, species within the genera Staphylococcus and Corynebacterium are usually present in moist areas, together with on the ft and the bends of the elbows. Species within the genus Propionibacterium, then again, are extra plentiful on the pores and skin websites which are richer in sebaceous glands, such because the scalp, the evaluation authors famous.

Why does pores and skin tan?

Close up of man on bike showing tan on his thigh.

Totally different individuals have completely different ranges of sensitivity to UV rays. (Picture credit score: Andrii Tymoshchuk / EyeEm by way of Getty Photographs)

Tanning is the pores and skin’s response to ultraviolet (UV) radiation. When pores and skin is uncovered to UV rays, it produces extra melanin pigments. Melanin is the primary line of protection in opposition to solar — it absorbs the UV rays and prevents them from damaging the pores and skin. When the quantity of UV mild exceeds the quantity of safety melanin can present, the radiation might result in sunburn, untimely pores and skin growing old, cataracts and even cancers, in keeping with Johns Hopkins Drugs (opens in new tab).

Individuals have completely different ranges of sensitivity to UV rays, relying on their age, well being standing and pores and skin kind. Adults over age 50, kids underneath 5, individuals with mild complexions and people with immune system deficiencies are usually extra at threat of dangerous results of tanning, in keeping with the Meals and Drug Administration (FDA) (opens in new tab).

“Though individuals with darker complexions are much less more likely to get pores and skin most cancers than individuals with lighter complexions, they will nonetheless develop malignancies and endure all types of UV harm,” the FDA notes.

How do tattoos keep on the pores and skin?

Professional African American tattoo artist makes a tattoo on client arm.

Needles from the tattoo machine punctures the pores and skin and deposits ink within the dermis layer. (Picture credit score: DAVID HERRAEZ by way of Alamy Inventory Picture)

Tattoos are made everlasting by puncturing the pores and skin and implanting ink down into a number of layers of the pores and skin dermis, Lucy Phillips (opens in new tab), dermatology nurse and managing director of Kaizen Medical in England, advised Stay Science by e-mail.

As soon as the ink is planted within the pores and skin, it’s taken up and saved by macrophages, a kind of immune cell. When these cells die, they launch the ink and cross it on to different macrophages. This fashion, the tattoos don’t “stain” the pores and skin cells, and they don’t seem to be perceived as a hazard by the immune system defenses, in keeping with a 2018 examine within the Journal of Experimental Drugs (opens in new tab).

As a normal rule, tattoos are protected if carried out in a correct institution, with clear devices and high-quality ink. Nevertheless, some individuals who get tattoos expertise problems. For instance, they could develop pores and skin infections akin to cellulitis, an an infection that impacts the pores and skin’s deepest layers, Phillips stated. (Cellulitis is to not be confused with cellulite, which is when fats within the pores and skin bulges by an overlying internet of connective tissue, making a dimpled look.)

Though tattoos are deemed everlasting, they are often eliminated by varied remedies, together with surgical procedure, chemical peels, and lasers that emit excessive energies that destroy tattoo ink, in keeping with a 2017 evaluation within the American Journal of Medical Dermatology (opens in new tab). The kind of laser used will depend on the affected person’s pores and skin colour, as some lasers take away melanin and melanin-producing cells referred to as melanocytes from the pores and skin, together with the ink-filled macrophages. Furthermore, some tattoo ink colours usually are not completely detachable, notably turquoise, yellow and purple, Phillips stated.

Why does pores and skin age?

photograph of elderly woman's hand beside a younger woman's hand.

Pores and skin ages attributable to each “intrinsic” and “extrinsic” components. (Picture credit score: Peter Finch by way of Getty Photographs)

With age, pores and skin turns into thinner, much less versatile and extra susceptible to wrinkles, dryness and age spots, also called liver spots. Bumps, cuts and different wounds additionally might take longer to heal, whereas small blood vessels could also be extra seen by pores and skin, in keeping with the Nationwide Institute on Growing older (opens in new tab). Aged pores and skin is characterised by a decreased variety of pores and skin cells and a breakdown of the pores and skin’s structural proteins, akin to collagen. In contrast with younger pores and skin, aged pores and skin additionally has increased ranges of irritation and skin-damaging free radicals, reactive molecules produced as a byproduct of metabolism, in keeping with a 2021 evaluation within the Worldwide Journal of Molecular Sciences (opens in new tab).

Pores and skin growing old could also be categorized as “intrinsic” or “extrinsic,” relying on the components which are driving the method, in keeping with a 2021 systematic evaluation and meta-analysis revealed within the journal Scientific Reviews (opens in new tab). Intrinsic growing old is instantly associated to an individual’s age and genetic make-up, whereas extrinsic growing old is influenced by environmental components, akin to air air pollution, diet, smoking and extreme tanning, the evaluation authors famous.

This text is for informational functions solely and isn’t meant to supply medical recommendation.

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