The skin: the essentials of its structure, its functions and its balance

15/01/2026

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Camille A.

Our skin is much more than just a covering. A fully-fledged organ, it is essential to the balance of our entire body. It protects us from the outside world while ensuring constant exchanges with our environment.
Getting to know your Understanding the structure, its roles, and the mechanisms that govern its balance is key to understanding the behavior of our skin and why some skin types become dry, sensitive, and reactive. or prone to skin imbalances.

In this article, you will find everything you need to know about skin, to better decode and understand it on a daily basis.

The skin, an essential organ of the human body

One of the largest organs of the body

Along with the intestines, the skin is one of the largest organs in our body. In adults, it represents on average¹:

1.5 to 2 m² of surface area,
Approximately 10% of body weight,
And its thickness varies depending on the area: from 0.5 mm at the eyelids to more than 4 mm on the soles of the feet.

The skin, the interface between the body and the environment

The skin constitutes a dynamic biological barrier between the body's internal environment and the external environment². As such, it is constantly exposed to various types of aggressions or stresses:

Physical aggressions such as cold, heat, UV rays, friction.
Chemical aggressions such as pollution, detergents, unsuitable cosmetic care.
Biological aggressions involving bacteria, viruses, and allergens.

The role of the skin is therefore to prevent the penetration of harmful substances while ensuring essential functions such as thermoregulation and sensory perception.

The skin's adaptive, defensive, and repair capabilities

The skin is a living organ with a remarkable capacity for continuous adaptation. Depending on its context, it can:

Strengthening one's barrier in response to aggression.
To trigger a controlled inflammatory response.
Repairing injuries through the healing process.

In addition to these responses, the skin knows how to regenerate. These abilities rely on close communication between skin cells, the immune system, and the nervous system.

To learn more about the skin healing process, see our full article .

Coupe de peau pour montrer les différentes couches de peau

Skin structure: a multilayered organization

L’épiderme, barrière cutanée

L’épiderme est la couche la plus superficielle de la peau. Il est majoritairement composé de cellules appelées kératinocytes, organisés en plusieurs couches et formant comme des « briques » assurant la structure épidermique.
D’autres types de cellules spécialisées interviennent dans l’épiderme comme :

Les mélanocytes, les cellules en charge de la production de mélanine, le pigment naturel de la peau.
Les cellules de Langerhans : ces cellules immunitaires assurent la défense de la peau contre bactéries, virus et champignons.

En surface de l’épiderme, on trouve la couche cornée, indispensable à la fonction barrière de la peau. Elle repose sur une organisation précise avec :

Des cellules spécifiques, les cornéocytes.
Un ciment lipidique intercellulaire composé de différents corps gras comme les céramides, le cholestérol, et des acides gras.
Et tout à la surface, le film hydrolipidique : un mélange invisible de sueur, d’eau et de sébum qui forme une barrière protectrice, limite la perte en eau, protège des agressions et maintient l’équilibre cutané.

Lorsque cette organisation est altérée, la fonction barrière est affaiblie, la peau devient plus perméable, favorisant la perte en eau, les irritations et la pénétration d’agents agressifs⁴.

The dermis, the skin's supporting tissue

Located beneath the epidermis, the dermis is a particularly interesting tissue due to its rich and varied composition with⁵:

Collagen fibers: non-extensible, these protein fibers give the skin its structure and resistance.
Elastin fibers: being stretchable, they are the source of skin elasticity.
Glycosaminoglycans, including hyaluronic acid: these complex compounds possess hygroscopic properties essential for hydration.
Characteristic cells, fibroblasts, are responsible for the synthesis of these different compounds and participate in skin repair mechanisms.

All of these elements together form the extracellular matrix (ECM), acting as a "cushion".

In addition to this, there are also⁵:

Blood vessels ensuring the diffusion of oxygen, water, and nutrients into the skin.
Nerve endings responsible for our various skin sensations, such as pain and thermal sensations of hot and cold.
The pilosebaceous follicles, the implantation sites of our hair and fur.
The sebaceous glands are responsible for the production of sebum.
Eccrine sweat glands, responsible for sweat.

With so many distinct compounds, the dermis appears as a major and complex layer of the skin, encompassing numerous functions.

The hypodermis, a protective and reserve tissue

The hypodermis is the deepest layer of the skin. Vascularized and innervated, it is mainly composed of adipose tissue formed by specialized cells, the adipocytes .

The hypodermis performs several important roles for the body⁶:

Mechanical protection, acting as a shock absorber and protecting deep structures (muscles, bones).
A factor in thermal regulation: adipose tissue participates in maintaining body temperature.
An energy reserve: adipocytes store energy in the form of lipids that can be mobilized when needed, and contribute to the balance of our overall metabolism.

The fundamental roles of the skin

Barrier function

The skin 's primary function is to maintain a barrier. This function relies mainly on the integrity of the epidermis and stratum corneum, which together form a physical, chemical, and biological barrier against external aggressors. An effective skin barrier limits the penetration of irritants, allergens, and microorganisms, while preventing transepidermal water loss, which is essential for maintaining hydration. When this barrier is compromised, the skin becomes more permeable, more sensitive, and more uncomfortable. Therefore, preserving the skin barrier is crucial for skin health and comfort.⁷

Sensory function

The skin is a major sensory organ, rich in nerve endings distributed across its entire surface. These nerve fibers allow us to perceive touch, pressure, pain, and temperature changes. This sensory function plays a fundamental role in protecting the body, providing rapid alerts in case of danger or aggression. It also allows the skin to adapt to its environment and modulate its physiological responses. Hypersensitivity of cutaneous nerve fibers can explain certain discomforts, such as those experienced by sensitive skin (tingling, burning sensations)⁷.

Immune function

The skin houses a veritable cutaneous immune system, composed of specialized cells capable of recognizing and neutralizing pathogens. These cells maintain constant surveillance and trigger appropriate immune responses in the event of an attack. This balance is finely regulated to protect without causing excessive inflammation. When this system is disrupted, disproportionate inflammatory reactions can occur, as seen in sensitive, reactive, or atopic-prone skin⁷.

To learn everything about atopic skin, see the dedicated article .

Regulatory and restorative functions

The skin actively participates in the body's thermoregulation through perspiration and the modulation of cutaneous blood vessels (vasodilation and vasoconstriction). It also plays a key role in tissue repair after injury, via various mechanisms such as inflammation, cell proliferation, and tissue remodeling. Overall, these processes help maintain and restore the skin barrier. When repair is impaired or incomplete, the skin becomes more fragile⁷.

Balance symbolisant l’équilibre de la peau

The delicate balance of the skin

A search for constant balance

The skin is a living system that constantly seeks to maintain several essential biological balances⁷:

Water balance: which aims for sufficient hydration at all levels, and low insensible water loss.
Lipid balance: ensured by the lipids of the epidermis and the stratum corneum, and by sebum, it is essential to the effectiveness of the skin barrier.
The balance of the skin flora: the skin harbors a skin microbiota whose balance is essential for protection against pathogens.
Energy balance: which ensures cell renewal and defense functions.

Maintaining these different balances conditions the well-being of the skin, including its comfort, tolerance, and resilience.

Factors that cause skin imbalance

Many factors can disrupt the overall skin balance and weaken the skin :

Environmental aggressors, such as pollution, UV radiation, cold or heat, impact the skin barrier.
Stress and fatigue also influence skin physiology via hormonal and inflammatory mediators.
Natural aging, on the other hand, leads to a natural decrease in lipids, hydration and repair capacities.
Finally, the use of unsuitable or overly aggressive skincare products can damage the skin barrier and amplify these imbalances.

The most common skin problems

When the skin 's balance is disrupted, visible or felt symptoms may appear:

A hydrolipidic imbalance can lead to dryness or dehydration.
Impairment of the barrier function and the cutaneous nervous system promotes hypersensitivity and hyper-reactivity.
Other imbalances can also lead to excess sebum or the appearance of pigment spots.

These different skin conditions indicate that the skin needs appropriate support to restore the natural balance of its physiology.

The impact of skin conditions on quality of life

As you've probably gathered, our skin is a complex organ whose condition significantly impacts our daily physical and emotional well-being. A visible and sensory organ, it directly influences our comfort, self-perception, and social interactions. Skin conditions such as severe dryness, hypersensitivity, atopic dermatitis (eczema), acne, or hyperpigmentation can cause discomfort, pain, itching, or aesthetic concerns, thus affecting our quality of life. Maintaining the balance and health of our skin therefore contributes significantly to our overall well-being.

Our skin is a living, intelligent organ, whose balance relies on a intricate organization and precise physiological mechanisms. Understanding its multi-layered structure, its various functions, and its potential imbalances allows us to adopt more respectful and effective skincare routines on a daily basis.
At TOPICREM, our skincare products are formulated to preserve the skin barrier, respect the skin's natural physiology, and meet its fundamental needs in all circumstances, regardless of its condition. Above all, their mission is to improve your comfort, bringing you greater well-being and serenity every day.

TOPICREM formulas have all been designed to provide protective hydration and preserve the skin barrier of sensitive skin for the whole family.

To do this, the laboratory relies on its expertise derived from pharmaceutical excellence:

Selection of high tolerance ingredients with proven effectiveness,
Development of formulas clinically tested on sensitive skin,
Effectiveness proven by science and approved by consumers.

Through the comfort and emotional well-being they provide, our treatments help you feel confident in your skin and in yourself, to better reveal yourself to others, and thus to fully enjoy every moment of life.

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FAQ – Structure and roles of the skin

What are the 3 main layers of the skin?

The skin is composed of three complementary layers. The epidermis forms the protective barrier on the surface, the dermis provides support, resistance and hydration, while the hypodermis protects, insulates from the cold and constitutes an essential energy reserve.

What is the purpose of the skin barrier?

The skin barrier protects the skin from external aggressors such as pollution and microorganisms. It limits water loss, helps maintain good hydration, and contributes to the comfort, tolerance, and overall balance of the skin.

Why does skin become dry or reactive?

Skin can become dry or reactive when its balance is disrupted. A decrease in lipids, excessive water loss, an unbalanced microbiota, or a weakened skin barrier can all contribute to discomfort, irritation, and hypersensitivity.

¹Bouslimani A, Porto C, Rath CM, Wang M, Guo Y, Gonzalez A, Berg-Lyon D, Ackermann G, Moeller Christensen GJ, Nakatsuji T, Zhang L, Borkowski AW, Meehan MJ, Dorrestein K, Gallo RL, Bandeira N, Knight R, Alexandrov T, Dorrestein PC. Molecular cartography of the human skin surface in 3D. Proc Natl Acad Sci US A. 2015 Apr 28;112(17):E2120-9. doi:10.1073/pnas.1424409112. Epub 2015 Mar 30. PMID: 25825778; PMCID: PMC4418856.

²Elias PM. Skin barrier function. Curr Allergy Asthma Rep. 2008 Jul;8(4):299-305. doi:10.1007/s11882-008-0048-0. PMID: 18606081; PMCID: PMC2843412.

³Chuong CM, Nickoloff BJ, Elias PM, Goldsmith LA, Macher E, Maderson PA, Sundberg JP, Tagami H, Plonka PM, Thestrup-Pederson K, Bernard BA, Schröder JM, Dotto P, Chang CM, Williams ML, Feingold KR, King LE, Kligman AM, Rees JL, Christophers E. What is the 'true' function of skin? Exp Dermatol. 2002 Apr;11(2):159-87. doi: 10.1034/j.1600-0625.2002.00112.x. PMID: 11994143; PMCID: PMC7010069.

⁴H, Alhajj M, Fakoya AO, Sharma S. Anatomy, Skin (Integument), Epidermis. 2024 Jun 8. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan–. PMID: 29262154.

⁵Brown TM, Krishnamurthy K. Histology, Dermis. 2022 Nov 14. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan–. PMID: 30570967.

⁶Liu M, Lu F, Feng J. Aging and homeostasis of the hypodermis in the age-related deterioration of skin function. Cell Death Dis. 2024 Jun 24;15(6):443. doi:10.1038/s41419-024-06818-z. PMID: 38914551; PMCID: PMC11196735.

⁷Chuong CM, Nickoloff BJ, Elias PM, Goldsmith LA, Macher E, Maderson PA, Sundberg JP, Tagami H, Plonka PM, Thestrup-Pederson K, Bernard BA, Schröder JM, Dotto P, Chang CM, Williams ML, Feingold KR, King LE, Kligman AM, Rees JL, Christophers E. What is the 'true' function of skin? Exp Dermatol. 2002 Apr;11(2):159-87. doi: 10.1034/j.1600-0625.2002.00112.x. PMID: 11994143; PMCID: PMC7010069.