dr hab. Anna Kołodziejczak — strona główna

Structure of the Skin and Functions of the Epidermis

Dr hab. Anna Kołodziejczak 13 min czytania

Close up of human hand skin with visible skin texture and lines
⚠️ Important legal information: This article is for educational purposes only and does not constitute medical advice. The information contained in the text does not replace consultations with a dermatologist or physician. In case of skin problems, allergic reactions, or doubts regarding skin condition, consult a qualified specialist. The author is not responsible for the consequences of using the described information.

📋 Table of contents

  1. Introduction to the structure of the skin
  2. Layers of the skin and their functions
  3. Epidermis – the first line of defense for the body
    1. Keratinocytes and the process of keratinization
    2. Melanocytes and UV protection
    3. Hydrolipid barrier of the epidermis
  4. Dermis – the foundation of elasticity
    1. Collagen and elastin
    2. Fibroblasts and skin renewal
    3. Blood vessels and the lymphatic system
  5. Subcutaneous tissue – insulation and protection
  6. How understanding the structure of the skin helps in care
  7. Frequently asked questions
  8. Summary

1. Introduction to the structure of the skin

The structure of the skin is fundamental knowledge for every cosmetologist, directly translating into the effectiveness of skincare treatments. The epidermis, dermis, and subcutaneous tissue are the three main layers that make up the largest organ of the human body, with a surface area of 1.5-2 m², serving as a protective barrier between the body and the external environment. Understanding the function of each layer allows for the conscious selection of active ingredients and care methods tailored to the individual needs of the skin.

💡 From the experience of a cosmetologist: In my 15 years of practice, the most common mistake clients make is 'blind’ care, without understanding how the individual layers of the skin work. For example: A client with dry skin used aggressive peels, not realizing that she was destroying the hydrolipid barrier of the epidermis. After 3 months of education and proper care – significant improvement in skin hydration and comfort.

2. Layers of the skin and their functions

Human skin consists of three essential layers, each serving specific functions and requiring a different approach in care. The thickness of the skin varies significantly depending on the location – from the delicate skin of the eyelids (0.05 mm) to the thick skin of the feet (up to 4 mm):

  • Epidermis (epidermis) – the outer protective layer with a thickness of 0.05-1.5 mm
  • Dermis (dermis) – the supportive layer of the skin mainly composed of fibrous connective tissue (collagen and elastic fibers), as well as a ground substance rich in hyaluronic acid
  • Subcutaneous tissue (hypodermis) – the deepest insulating layer containing fat cells

Each of these layers contains different types of cells, supporting structures, and transport systems that work together in the processes of regeneration, protection, and thermoregulation of the body.

Layer Thickness Main cells Key functions Impact on skincare
Epidermis 0.05-1.5 mm Keratinocytes (95%), melanocytes Protective barrier, keratin production Low molecular weight ingredients, gentle cleansing
Dermis 1-4 mm Fibroblasts (70-80%), macrophages, immune and vascular cells Elasticity, strength Contouring treatments, thermoregulation – impact on lipolysis modulation
Subcutaneous tissue Variable Adipocytes (fat cells) Insulation, energy storage Contouring treatments, thermoregulation

3. Epidermis – the first line of defense for the body

The epidermis is the outermost layer of the skin, which undergoes constant renewal. The regeneration process of the epidermis takes about 28 days in young individuals, but with age, it can extend to 45-60 days. In my cosmetic practice, I observe that this aspect often determines the effectiveness of skincare treatments.

3.1. Keratinocytes and the keratinization process

Keratinocytes make up about 95% of the epidermal cells and are responsible for producing keratin – the protein that builds the skin’s protective barrier. In the keratinization process, cells move from the basal layer towards the surface, gradually losing their nuclei and transforming into dead scales that naturally shed from the skin’s surface.

Practical significance: Understanding the renewal cycle of keratinocytes allows for optimal planning of exfoliating treatments. Enzymatic or mechanical peels should be tailored to the skin’s natural renewal rhythm.

3.2. Melanocytes and UV protection

Melanocytes are cells that produce melanin – the pigment responsible for skin color and protection against UV radiation. One melanocyte collaborates with about 36 keratinocytes to form a melanin unit. UV radiation (UVA and UVB) stimulates melanin production, but excessive exposure can lead to DNA damage. HEV and IR radiation also affect melanocyte activity, which in practice means the need for broad-spectrum protective filters.

3.3. Hydrolipid barrier of the epidermis

It is important to note that the hydrolipid layer/barrier (hydrolipid mantle/film) is often confused with the intercellular cement of the stratum corneum, and these are not identical structures! The hydrolipid barrier (hydrolipid film) is a mixture of sebum and sweat components, whose composition is not constant and changes depending on age, skin type, or condition. Meanwhile, the integrity of the epidermis is ensured by the so-called lipid cement in the stratum corneum, which is dominated by three groups of lipids: ceramides (about 50%), cholesterol (about 25%), and free fatty acids (about 10-15%). This protective layer is crucial for maintaining proper skin hydration and protection against harmful external factors.

💡 Observations from practice: Clients with a weakened hydrolipid barrier often complain of tightness, skin peeling, and increased sensitivity to cosmetics. Rebuilding the barrier sometimes requires 4-8 weeks of consistent care.

4. The dermis – the foundation of elasticity

The dermis is the layer responsible for mechanical strength, elasticity, and youthful appearance of the skin. It consists of two sub-layers: the papillary dermis (upper) and the reticular dermis (deeper), which differ in the density of collagen and elastin fibers. The connective tissue in this layer provides structural support for blood vessels and nerve fibers ending in specialized receptors responsible for touch, pain, and thermal perception.

4.1. Collagen and elastin

Collagen makes up about 70-80% of the dry mass of the dermis and is responsible for its strength. Elastin, although it constitutes only 2-4%, is crucial for skin elasticity. After the age of 25, collagen production decreases by about 1% per year, leading to a gradual loss of skin firmness.

Active ingredients supporting collagen: In cosmetic practice, we effectively use ingredients that stimulate collagen synthesis, such as peptides, vitamin C, or retinol. NOTE: Retinol requires consultation with a specialist and gradual introduction.

4.2. Fibroblasts and skin renewal

Fibroblasts are the cells responsible for synthesizing collagen, elastin, and hyaluronic acid. Cosmetic literature indicates that with age, their activity may gradually decrease, which can affect the texture and elasticity of the skin. Active substances such as hyaluronic acid in home care can support fibroblast functions.

🧬 Observations from cosmetic practice: In my work, I notice that some skin types may exhibit reduced elasticity after prolonged inflammatory conditions and due to ongoing micro-inflammation referred to as inflammaging. Such skin often requires longer supportive care and systematic use of ingredients that promote regeneration. NOTE: In case of skin problems, always consult a dermatologist before introducing intensive care.

4.3. Blood vessels and the lymphatic system

Blood vessels in the dermis are responsible for delivering nutrients and oxygen to cells and removing metabolic waste products. The lymphatic system supports tissue drainage and the immune response. Proper circulation of blood and lymph affects skin tone and the speed of regeneration.

5. Subcutaneous tissue – insulation and protection

Subcutaneous tissue mainly consists of fat cells (adipocytes) grouped into fat lobules (clusters of adipocytes) separated by connective tissue septa, through which blood vessels and nerves run. It serves insulating and protective functions and acts as an energy reservoir for the body. The thickness of subcutaneous tissue varies depending on the body part and can affect the effectiveness of certain cosmetic treatments.

Sweat and sebaceous glands: The subcutaneous tissue houses eccrine sweat glands, apocrine sweat glands, and sebaceous glands. Eccrine sweat glands are responsible for thermoregulation by secreting watery sweat, while apocrine sweat glands (in the armpits, groin) produce sweat rich in proteins and lipids. Sebaceous glands secrete sebum through pores to the skin’s surface, forming a natural component of the hydrolipid mantle. Fat cells in this layer provide insulation and serve as an energy reservoir.

6. How knowledge of skin structure aids in care

Understanding the structure of the skin directly translates to the effectiveness of cosmetic treatments and home care. This allows us to:

  • Select appropriate active ingredients – ceramides for barrier reinforcement, peptides for collagen stimulation
  • Plan optimal routines – considering the skin renewal cycle and circadian rhythm
  • Avoid skincare mistakes – that may weaken the skin’s protective barrier
  • Understanding the mechanism of treatments – from peels to massages
💡 Practical advice: Clients who understand the structure of their skin are less likely to abandon their regular skincare routine. They know that results take time – at least one full cycle of skin renewal (28-45 days depending on age).

💡 Observations from cosmetic practice

Observation: „The cream does not absorb, it remains on the surface”
Possible causes: Incorrectly chosen consistency or weakened skin barrier function
May help: Consultation with a cosmetologist regarding gentle exfoliation and lighter textures
Observation: „The skin shines just 2 hours after washing”
Possible causes: The skin may react to overly intense cleansing
May help: Gentler cleansing products and proper hydration under the supervision of a specialist
Observation: „Pigmentation persists despite skincare”
Possible causes: Lack of consistent sun protection
May help: Consultation with a dermatologist and systematic SPF protection
⚠️ Important: The above observations are educational in nature. In case of skin problems, always consult a dermatologist or cosmetologist.

In the case of facial skin, which differs from body skin due to thinner epidermis and higher density of sebaceous glands, care requires particular gentleness. Physical activity affects all layers of the skin by improving circulation and increasing the rate of cell renewal.

❓ Frequently asked questions

What is the structure of the skin and what are its functions?
The skin consists of three main layers: the epidermis, the dermis, and the hypodermis. Each layer contains different types of cells and structures that work together in processes of protection, regeneration, and thermoregulation. The epidermis serves as an external protective barrier, the dermis is responsible for elasticity, firmness, and nourishment, while the hypodermis acts as natural insulation and energy storage. Each of these layers has its unique structure and functions that complement each other. This allows the skin to protect the body from external factors, help maintain proper hydration, participate in immune responses, enable the sensation of environmental stimuli, assist in healing processes, and support thermoregulation.
What are the 4 layers that make up the skin’s protective barrier?
The skin’s protective barrier is a complex system consisting of four elements. The physical barrier is created by the epidermal cells: keratinocytes and corneocytes. The chemical barrier includes the natural moisturizing factor (NMF), lipids of the hydrolipid mantle, and intercellular cement lipids responsible for the integrity of the epidermis and preventing water loss, as well as an acidic pH that supports regeneration and has antibacterial properties. The microbiotic barrier is the skin’s natural microbiome. The immunological barrier consists of immune system cells that maintain its homeostasis. The significant role of the auxiliary antioxidant barrier of the skin is also highlighted.
What are the 5 functions of the skin?
The five main functions of the skin are: 1) protection against external factors, 2) thermoregulation of the body, 3) sensory perception, 4) synthesis of vitamin D, 5) immunological function and barrier against pathogens.
What are the layers of the epidermis in order?
The layers of the epidermis from deep to superficial are: the basal layer (stratum basale), the spinous layer (stratum spinosum), the granular layer (stratum granulosum), the clear layer (stratum lucidum – only in thick skin), and the horny layer (stratum corneum).
Can fibroblast functions be supported in home care?
In the cosmetic literature, we find information about ingredients that can support skin regeneration processes, such as peptides or vitamin C. In my practice, I often observe positive effects from the systematic use of such ingredients under the supervision of a specialist. However, each skin reacts individually, so consulting with a cosmetologist is important.
Why might some active ingredients not deliver the expected effects?
The effectiveness of cosmetics depends on the chemical form and concentration of the cosmetic ingredients, the carrier and pH of the preparation, as well as the stability of the ingredient and even the type of packaging. The condition of the skin, regularity of use, interactions with other products, and sun protection also play a significant role. In many cases, effects appear only after several weeks of systematic care, so it is best to consult a cosmetologist for product selection.

7. Summary

The structure of the skin is a complex system of three layers – the epidermis, dermis, and subcutaneous tissue – that work together in the processes of protection, regeneration, and maintaining the body’s homeostasis. The epidermis serves as a protective barrier thanks to keratinocytes and melanocytes, the dermis provides elasticity through collagen and elastin produced by fibroblasts, and the subcutaneous tissue offers thermal and mechanical insulation.

💡 EXPERT SUMMARY

„In my cosmetic practice, I observe that clients who understand the structure of their skin are more systematic in their care and more often achieve satisfactory results. Knowing how the individual layers function helps in the conscious selection of care.”

— Anna Kołodziejczak, cosmetologist

⏱️
28-60 days
Approximate time for the renewal cycle of the epidermis
📏
0.05-4mm
Range of skin thickness on the body
🔬
~95%
Estimated proportion of keratinocytes in the epidermis
🎯 Key takeaways to remember:
  1. Each layer has different needs – there is no universal care
  2. Age changes all parameters – the routine must evolve
  3. The hydrolipid barrier is fundamental – without it, no active ingredients will work
  4. Patience is key – the skin needs at least one renewal cycle for visible effects

In cosmetic practice, this information translates into better treatment results and greater client satisfaction, as they understand the processes occurring in their skin. A detailed guide to facial care at home will help you apply this knowledge in your daily routine.

🎯 ACTION PLAN: How to use knowledge about skin structure

📅 WEEKS 1-2: Diagnosis
  • Observe the thickness of the skin in different areas
  • Check how quickly cosmetics are absorbed
  • Perform an elasticity test (pinch test)
🧴 WEEKS 3-4: Adjustment
  • Choose textures based on the thickness of the epidermis
  • Adjust the intensity of cleansing
  • Introduce ingredients that support the barrier
🔬 MONTHS 2-3: Optimization
  • Introduce active ingredients (under supervision)
  • Monitor reactions of all layers
  • Adjust the routine to the renewal cycle
💡 Pro tip: Take photos every 2 weeks in the same lighting. Changes in skin structure are gradual and can easily be missed without documentation.
⚠️ Final disclaimer: All information contained in the article is for educational purposes only and does not constitute medical or cosmetic advice. It does not replace professional consultation with a dermatologist or qualified cosmetologist. The observations presented from cosmetic practice are for informational purposes only. In case of skin problems, unusual reactions, doubts about skin condition, or before introducing new active ingredients into your care routine, always consult the appropriate specialist. The effects of skincare are highly individual and may vary depending on skin type, age, health status, and many other factors. The author is not responsible for the consequences of using the described information. Pregnant and breastfeeding women should consult any changes in care with a doctor.

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