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Entry

List of abbreviation

1. Anatomy and physiology of skin and hair

1.1. Structure and functions of the skin

1.1.1. Epidermis

1.1.2. Basal cell layer (stratum basale)

1.1.3. Layer of spiny cells (stratum spinosum)

1.1.4. Granular cell layer (stratum granulosum)

1.1.5. Light layer of the epidermis (stratum lucidum)

1.1.6. Corner cell layer (stratum corneum)

1.1.7. Dermis (corium, dermis)

1.1.8. Reticular layer (stratum reticulare)

1.1.9. Subpapillary layer (stratum subpapillare)

1.1.10. Papillary layer (stratum papillare)

1.1.11. Skin appendages (adnexa cutis)

1.1.12. Subcutaneous tissue (tela subcutanea, subcutis)

1.2. Hair structure and physiology

1.2.1. Hair follicle stem cells

1.2.2. Hair pigmentation

1.2.3. Oxidative stress

1.3. Hair follicle embryology

1.4. Hair biochemistry

1.4.1. Amino acids

1.4.2. pH of the scalp and hair

1.5. Hair growth cycle

1.5.1. Anagen

1.5.2. Catagen

1.5.3. Telogen

1.5.4. Exogenous

1.5.5. Kenogen

1.6. Types of hair and their properties

1.6.1. Classification according to hair type

1.6.2. Classification according to hair type

1.6.3. Andre Walker’s classification

1.6.4. Classification according to the structure of the hair

1.6.5. Classification by ethnicity

1.7. Hair shaft – defects of hair shaft

1.7.1. Hair shaft anomalies

1.8. Changes in the character of the hair – chemical, mechanical and thermal damage

1.8.1. Chemical damage

1.8.2. Damage to the hair shaft

1.8.3. Dystrophic hair

2. Excessive hair loss

2.1. Factors affecting excessive loss hair

2.1.1. The role of glycosaminoglycans

2.1.2. Excessive hair loss at women

2.1.3. Air pollution – its role in excessive hair loss

2.2. Factors affecting hair growth

3. Types of balding

3.1. Alopecia areata

3.2. Androgenic alopecia in men

3.3. Androgenic alopecia in women

3.4. Menopausal androgenic alopEcia in women

3.5. Telogen general alopecia

3.6. Anagen alopecia

3.7. Scaring alopecia

3.8. Drug-based alopecia

3.9. Systemic-related alopecia oncological therapy

3.10. Trichotillomania

4. Dermatological diseases of the scalp

4.1. Mycosis of the scalp

4.2. Atopic dermatitis of the scalp

4.3. Seborrhea

4.4. Seborrhous skinititis of the scalp

4.5. Psoriasis of the scalp

4.6. Dandruff – white, varied, pink

4.7. Allergic changes in hair scalp

4.8. Pediculosis/Lice

4.9. Demodecosis

4.10. Inflammation of follicle

4.10.1. Malassezia folliculiti

4.10.2. Bacterial folliculitis

4.10.3. Folliculitis decalvans

5. Diagnostic methods in trichology

5.1. Trichological patient in laboratory diagnostics

5.2. Basic trichological diagnostic methods

5.2.1. Physical examination

5.2.2. Pull test

5.2.3. Washing test

5.2.4. Hair weighing method

5.3. Trichological patient imagie diagnostics

5.3.1. Trichoscopy

5.3.2. Trichogram

5.3.3. Phototrichogram

5.3.4. Scalp biopsy

5.3.5. Wood’s lamp

5.4. Imaging methods of hairy skin head and hair

5.4.1. Light microscopy

5.4.2. Polarized light microscopy

5.4.3. Confocal microscopy

5.4.4. Electron microscopy

5.5. Apparatus for physicotherapy in trichology

5.5.1. Darsonvalization

5.5.2. Electrostimulation

5.5.3. Ultrasounds

5.5.4. Cryomassage

5.6. Elemental analysis of hair

6. Scalp care in the trichological practice

6.1. Scalp cleansing treatment

6.2. Cavitation peeling of the scalp

6.3. Scalp darsonvalization treatment

6.4. Scalp ionophooresis

6.5. Carboxytherapy of the scalp

6.6. Needle mesotherapy of the scalp

6.6.1. Needle mesotherapy

6.6.2. Needle mesotherapy of the scalp

6.7. Microneedle mesotherapy of the scalp

6.8. Needle mesotherapy of the skin heads using plasma platerich

6.8.1. Platelet-rich plasma

6.8.2. Platelet-rich plasma in the treatment of baldness

6.8.3. Platelet-rich fibrin

6.9. Stem cells in balding therapy

6.9.1. Hair follicle stem cells

6.9.2. Micrografts

6.9.3. Autologous CD34+ stem cells and concentrated growth factors

6.10. LED therapy

6.11. Laser therapy

6.11.1. LLLT technology

6.11.2. Fractional laser

6.11.3. Excimer laser

6.12. Oxygen infusion

6.13. Scalp massage

6.14. Botulinum toxin in baldness treatment – a new potential therapeutic option

7. Hair care

7.1. Rules of correct hair care

7.1.1. Shampoos

7.1.2. Hair conditioners

7.2. Chemical hair treatments

7.2.1. Hair coloring preparations

7.2.2. Hair lightening agents

7.2.3. Chemical hair straightening

7.2.4. Permanent wave

7.3. Effects of improper hair care

7.4. Penetration/transport routes of trichological preparations

7.4.1. Stages of penetration of active ingredients

7.4.2. The influence of the preparation’s formulation on the absorption of the active substance

7.4.3. Nanotechnology in the transport of active ingredients

7.4.4. Techniques for transporting active ingredients

7.4.5. Permeation promoters

8. Ingredients of trichological preparations

8.1. List of ingredients used in trichological preparations along with description

8.1.1. Antioxidants, vitamins and macroelements

8.1.2. Plant extracts

8.1.3. Oils and essential oils

8.1.4. The most frequently used active ingredients

8.1.5. Complexes of active ingredients

8.1.6. Plant stem cells and cell activating ingredients hair follicle stem

9. Non-surgical completion hair methods

9.1. Scalp micropigmentation – characteristics, treatment techniques

9.2. Hair loss retouch

10. Hair transplantation

10.1. Qualification of a trichological patient for hair transplant

10.2. Overview of hair transplantation methods

10.2.1. FUE (follicular unit excision) hair transplant method

10.2.2. Suturing technique (trichophytic closure, TC)

10.2.3. Platelet-rich plasma (PRP)

10.2.4. DHI (direct hair implantation) hair transplant method

10.2.5. SAFER system (suction assisted follicular extraction and reimplantation)

10.2.6. Biofibre synthetic graft

10.3. Indications and contraindications for hair transplant

10.4. Post-procedure recommendations

11. Pharmacology in trichology

11.1. Groups of medications for women, contraindications, interactions

11.1.1. Female pattern androgenetic alopecia

11.2. Groups of medications for men, contraindications, interactions

11.2.1. Androgenetic alopecia male pattern

11.2.2. Alopecia areata in women and men

12. Basics endocrinology

12.1. Function of the hormonal system and its effect on excessive hair loss

12.1.1. Hypothyroidism

12.1.2. Hyperthyroidism

12.1.3. Hashimoto’s thyroiditis

12.1.4. Graves’ disease

12.1.5. Excessive hair

12.1.6. Sex hormones

13. Trichological dietetics

13.1. Diet and supplementation

13.1.1. Vitamins

13.1.2. Proteins, fats and carbohydrates

13.1.3. Micro- and macroelements – main elements, trace elements

13.2. Intestinal microbiome and impact on the condition of the scalp

13.2.1. The relationship between telogen effluvium and the microbiome intestinal

13.2.2. The relationship between androgenic alopecia and the microbiome intestinal

13.2.3. The relationship between alopecia areata and the microbiome intestinal

13.2.4. The relationship between alopecia areata and hypothyroidism thyroid and intestinal microbiome

13.2.5. Restoration of immune privilege

13.2.6. Anti-inflammatory diet

13.2.7. Alopecia due to malnutrition

14. Organization of work in the trichological office

14.1. Procedures in the trichological office

14.1.1. Organization of a trichology office

14.1.2. Patient diagnostics

14.2. Hazards in the trichology office

14.3. Interview with a trichological patient

Literature

About the Author

Other chapters are available in the full version of the e-book.

Entry

Trikhos in Greek means hair, from which comes the name trichology, i.e. the study of hair. Trichology is a field of medicine that covers the diagnosis of scalp and hair diseases, as well as the treatment and care process.

In order to properly diagnose, interpret, and analyze scalp disease, it is essential to understand the biology of the skin and its appendages. The structure of the hair shaft may initially seem quite simple, but in fact it is a complex part of the anatomy. Proper histopathological evaluation of scalp dermatoses should be based on an understanding of the structure of the basic unit, hair follicles and all associated structures. The book covers the full spectrum of trichopathology, essential for proper understanding trichoscopic image of the patient, from the anatomy and physiology of the scalp and hair, to the classification of scalp diseases, facilitating the proper interpretation of the patient’s clinical data.

The following chapters include clinical features, pathogenesis, as well as medical treatment in relation to individual dermatoses, laboratory diagnostics, and also histological features with clinical description, trichoscopic features, and classification of hair types and types of hair damage. They allow proper understanding of the pathophysiology and clinical presentations, as well as the therapeutic and surgical therapies used. However, it is necessary to emphasize the importance of proper care of the scalp and hair in the field of cosmetological trichology, which is necessary to achieve results acceptable to patients.

The aim of the publication was also to describe comprehensively diseases of the scalp, in medical, cosmetological and surgical terms. Without following previous models, the treatment text as well as the characterization of individual scalp disorders specifically addresses their molecular basis in a complex manner.

Subsequently, such important issues as the basics of endocrinology, dietetics and the organization of work in a trichology office were discussed. The book covers the full range of knowledge necessary to work with a trichological patient.

The range of recipients of the publication is very wide. Both students and practicing trichologists, dermatologists and cosmetologists involved in the treatment of patients with excessive hair loss will probably find the presented content helpful and practical.

PhD Claudia Musiał

List of abbreviation

1 CE (Conformité Européenne) – European conformity (certificate)

17-OH-P – 17-hydroxyprogesterone

18-MEA – 18-methylicosanoic acid located in the upper β layer of the cell membrane complex

2A ADP – adenosine diphosphate, adenosine-5’-diphosphate

2D – two-dimensional

3 NT-4 – neurotrophin 4

3D – three-dimensional

4 Bmpr2 – bone morphogenetic protein receptor type 2

5 FSH – follicle-stimulating hormone

5α-R – 5α-reductase

AA – amino acids

AA/ARA – arachidonic acid

ACR – autologous cellular renewal

Acvr2a – activin receptor type-2A precursor

AD – atopic dermatitis

AIDS – acquired immunodeficiency syndrome

ALA – alpha-lipoic acid

Ala, A – alanine

ALT – alanine aminotransferase

ANA – antinuclear antibodies: ANA-1, ANA-2, ANA-3

APUD – amine precursor uptake and decarboxylation, a system of scattered endocrine cells

Arg, R – arginine

Asn, N, Asp-NH2 – asparagine

Asp, D – aspartic acid

AST – aspartate aminotransferase

ATg – thyroglobulin antibody, antibodies specific to thyroglobulin (Tg)

ATP – adenosine-5-triphosphoric acid

ATPO – anti-thyroid peroxidase, antibodies against peroxidase

Bcl-2 – a protein involved in the inhibition of apoptosis (mediated by Bax proteins and Bak) proteins from the Bcl-2 family (Bcl-2 family)

Bcl-2 – B-cell lymphoma 2, a heterogeneous group of proteins whose name comes from B2 cell lymphoma

BCS1L – ubiquinol-cytochrome C reductase complex chaperone

BDNF – brain-derived neurotrophic factor – neurotrophic factor of origin cerebral

BM – bone morphogenetic proteins

BM-CSPG – basement membrane chondroitin sulfate proteoglycan – core protein chondroitin sulfate proteoglycan

BMF – bone marrow failure

BMP2 – bone morphogenetic protein 2

BMP4 – bone morphogenetic protein

BRAF – type B rapid accelerated fibrosarcoma – BRAF proto-oncogenic kinase

Ca – calcium

CAT – catalase

CBC – complete blood count

CD1+ – cluster of differentiation 1 – a protein belonging to supergenes immunoglobulins composed of MHC class 1 glycoproteins

CD34 – cluster of differentiation 34, hematopoietic progenitor cell antigen

CD34 CD44 – cluster of differentiation 44 – glycoprotein, hyaluronic acid receptor located in the basement membrane of the follicle

CD8+ – cluster of differentiation 8 – membrane glycoprotein associated with MHC class

CGF – concentrated growth factors

CI (Color Index) – number assigned to dyes

CLA – conjugated linoleic acid

CLEC16A – a family of 16 C-type lectin domains

CO2 – carbon dioxide

COX2 – cyclooxygenase-2

CRP – C-reactive protein

CS – chondroitin sulfate

CTLA4 – cytotoxic T-lymphocyte associated protein 4 – a protein encoded by the CTLA4 gene located on the surface of T lymphocytes

Cu (cuprum) – copper

CYP19A1 – cytochrome P450 family 19, subfamily A1

CYPP450 – cytrochrome p450 – cytochrome from the group of enzymes (transmembrane proteins)

Cys-SH, C – cysteine

Cys-S-S-Cys – cystine

Da – dalton

DCPC – diphenylcyclopropenone

DHA – docosahexaenoic acid

DHEA – dehydroepiandrosterone sulfate

DHI – direct hair implantation – implantation of hair follicles (using a medical pen)

DHT – dihydrotestosterone

DMSO – dimethyl sulfoxide

DNA – deoxyribonucleic acid

DNCB (2,4-dinitrochlorobenzene) – dinitrochlorobenzene

DS – dermatan sulfate

E2 – estradiol

EBOV – Ebola virus

EC – epicatechin, (-)-epicatechin

ECG – epicatechin gallate, (-)-epicatechin 3-gallate

ECGF – endothelial cell growth factor

ECM – extracellular matrix

EDTA – Disodium EDTA; Ethylenediaminetetraacetic acid – edetic acid

EGC – epigallocatechin, (-)-epigallocatechin

EGCG – epigallocatechin gallate, (-)-epigallocatechin-3-gallate

EGF – epidermal growth factor

eGFR – estimated glomerular filtration rate – laboratory test determining estimated glomerular filtration rate by measurement creatinine clearance

ENA – extractable nuclear antigen – soluble nuclear antigens

EPA – eicosapentaenoic acid

ER – estrogen receptors

Er:YAG – erbium-yag fractional ablative laser

ERBB3 Erb-B2 receptor tyrosine kinase 3 – receptor (HER3)

ERCC2 – XPD – eroderma pigmentosum complementary group D, ERCC excision repair 2– the gene encoding the mRNA, XPD protein is a polypeptide composed of amino acids

ERCC3/XPB – RCC Excision Repair 3, TFIIH Core Complex Helicase Subunit – helicase TFIIH transcription factor complex (transcription factor II H)

ERK – extracellular-signal-regulated protein kinase – ERK group kinases respond for cell proliferation and differentiation

ESR – erythrocyte sedimentation rate – the rate of erythrocyte sedimentation

ESR (Biernacki’s test) – erythrocyte sedimentation rate (ESR)

FAD – flavin adenine dinucleotide, coenzyme, a compound that conditions the scalp and hair follicles

FDA – American Food and Drug Administration

Fe – ferrum – iron

FGF – a fibroblast growth factor that is involved in the process of angiogenesis

FGF-5 – fibroblast growth factor 5

FT – free testosterone

FT3– triiodothyronine, concentration of free triiodothyronine (T3)

FT4 – free throxine – thyroxine (T4)

FU – follicular unit – a group of hair follicles

FUE – follicular unit excision – transplantation of individual hair follicles

GAG – glycosaminoglycans

GLA – gamma linolenic acid – γ-linolenic acid Gln, Q,

Glu, E – glutamic acid

GLu-NH2 – glutamine

Gly, G (glycine) – glycine

GPT – glutamine-pyruvic transferase

GSH – glutathione

GTF2H5 – general transcription factor IIH subunit 5 – subunit 5 of the general factor transcriptional IIH, a protein encoded by the GTF2H5 gene

HA – hyaluronic acid

HBV – type B hepatitis virus

HCV – type C hepatitis virus

HDL – high density lipoprotein – one of the total cholesterol fractions, high density lipoprotein

He-Ne – helium-neon laser

Hep – heparin

HFS – hair follicle simulation – medical dermatography

hfSC – hair follicle stem cells

HGF – hepatocyte growth factor – hepatocyte growth factor

His, H – histidine

HIV – human immunodeficiency virus

HLA-Cw6 – human leukocyte antigen Cw6, a gene linked to psoriasis

HLA-DR – cell surface receptor MHC (major histocompatibility complex) class II

HPCA-1 – hydrogen peroxide sensor – a class of receptor-like kinases rich in leucine

HPV – human papillomavirus

HRT – hormone replacement therapy

HS – heparan sulfate

HSPGs – Heparan sulfate proteoglycans – heparan sulfate, a polysaccharide from the group glycosaminoglycans

Hz – hertz

I.D.P. (Intra Dermique Profond) – deep intradermal injection

I.D.S. (Intra Dermique Superficielle) – superficial intradermal injection

I.E.D. (Intra Epi Dermique) – intraepidermal injection

I.H.D. (Intra Hypo Dermique) – subcutaneous injection

IBS – irritable bowel syndrome

IgE – immunoglobulin E

IGF-1 – insulin-like growth factor 1

IGF-2 – insulin-like growth factor 2

IL – interleukins, cytokines crucial for inflammatory processes

IL2RA – interleukin-2 receptor alpha chain [CD25] – the α chain of the interleukin 2 receptor

INCI – International Nomenclature of Cosmetic Ingredient

IPL – intense pulsed light source

IR – infrared light

KGF – keratinocyte growth factor

kHz – kilohertz

KOH – potassium hydroxide solution

KRT81 (keratin 81) – type II keratin Hb1, encoded before the KRT81 gene

KRT83 (keratin 83) – type II keratin, encoded before the KRT83 gene

KRT86 (keratin 86) – type II Hb6 keratin, encoded before the KRT83 gene

KS – keratan sulfate

LAHS – loose anagen hair syndrome anagen

LDL – low-density lipoprotein

LED – light-emitting diode

Leu, L – leucine

LH – luteotropic hormone

Lhx2 (LIM Homeobox 2) – transcription factor

lle, I – isoleucine

LLLT (low level laser therapy) – low-level laser (laser technology soft)

LOX – lipoxygenase

LTB4 – leukitriene B4

LTB5 – leukotriene B5

LXA4 – lipoxin A4

Lys, K – lysine

Lys-OH – hydroxylysine

M – methionine

mA – milliampere

Matrix GLA – matrix GLA protein

MC1R (melanocortin 1 receptor) – also known as melanocortin type 1 receptor as MSHR (melanocyte-stimulating hormone receptor)

MCH (mean corpuscular hemoglobin) – average mass of hemoglobin of blood cells red ones

MCHC (mean corpuscular hemoglobin concentration) – average hemoglobin concentration in red blood cells

MCV (mean corpuscular volume) – average volume of red blood cells Met,

Mg – magnesium

mGKS – local glucocorticosteroids

mIK – local calcineurin inhibitors

miR-24 (MicroRNA 24-1) – an RNA gene associated with the miRNA class MRSA (methicyllin-resistant Staphylococcus aureus) for methicillin

MSM – methylsulfonylmethane

N_2O – nitrous oxide

NaCl – sodium chloride

NAD – nicotinamide adenine dinucleotide, coenzyme, a compound that conditions the scalp and hair follicles

NFATc1 (nuclear factor of activated T cells 1) – cytoplasmic signaling pathway1

NF-kB (nuclear factor kappa-light-chain-enhancer of activated B cells) – transcriptional NF Kappa B

NGF (nerve growth factor) – transcription factor

NMF – a natural moisturizing factor

NO – nitrogen oxide

NSAIDs – non-steroidal anti-inflammatory drugs nm – nanometer

NT-3 – neurotrophin-3

O3 – ozone

OHS – Occupational health and safety

ORS – outer root sheath – a bulge of the outer sheath of the hair

OX-2 (CD200) – OX-2 membrane glycoprotein, human encoded protein by the CD200 gene

P.P.P. – point by point

PABA – para-aminobenzoic acid

PAHs – polycyclic aromatic hydrocarbons

PCOS – polycystic ovary syndrome

PCR – polymerase chain reaction

PDGF – the platelet-derived growth factor responsible for cell growth and division (skin and epidermis cells)

PFS – post-finasteride syndrome

PGE2 – prostaglandin E2

PGE3 – prostaglandin E3

Phe, F – phenylalanine

PLT – platelets

PM – particulate matter – solid particles

PM10 – particles with a diameter of 10 μm (or less)

PM2.5 – particles with a diameter of 2.5 μm (or less)

PPD – paraphenylenediamine

PRF – plate-rich fibrin

PRL – prolactin, lactotropic hormone, lactotropin

Pro, P – proline

Pro-OH – hydroxyproline

PRP – platelet-rich plasma

PTD – paratoluenediamine – 2,5-diaminotoluene sulfate (2,5-toluenediamine sulfate, C 7 H10 N2, CI 7604)

PUVA – Psoralen Ultraviolet-A - photochemotherapy, oral administration of psolarens and UV exposure

RCM – reflection confocal microscopy

RECQL4 (RecQ Like Helicase 4) – DNA helicase Q4, enzyme encoded by the RECQL4 gene

ROS – reactive oxygen species

S – sulfur

SADBE – squaric acid dibutyl ester

SAFER – suction assisted follicular extraction and reimplantation-vacuum hair extraction and implantation

SARS-CoV-2 – severe acute respiratory syndrome coronavirus 2 – syndrome coronavirus 2 severe acute respiratory failure

Se – selenium

SEM – scanning electron microscopy

Ser, S – serine

SHH (sonic hedgehog) – protein encoded by the SHH gene

Si (silicium) – silicon

SLS – sodium lauryl sulfate

SOD – superoxide dismutase

T – tocopherols

T3 – tocotrienols

TC (trichophytic closure) – technique of applying a trichophytic suture (sewing technique)

TCDD – 2-, 3-, 7-, 8-tetrachlorodibenzo-p-dioxin

TCF3 – transcription factor 3

TEM – transmission electron microscopy

TFIIH core complex helicase subunithelicase – transcription factor subunit TFIIH

TGF-β – transforming growth factor β tumors

Thr, T – threonine

TIBC – total iron binding capacity

TNF-α – tumor necrosis factor α)

TPP – thiamine pyrophosphate, cocarboxylase, coenzyme, compound conditioning the scalp and hair follicles

TRAb/TBII (thyroid stimulating hormone receptor antibody/thyrotropin-binding inhibitors immunoglobulins) – antibodies that inhibit the binding of thyrotropin (TSH)

Trp, W – tryptophan

TSH – thyroid-stimulating hormone, thyrotropin

TT – total testosterone

Tyr, Y – tyrosine

ULBP3 – UL16 binding protein 3

ULBP6 – UL16-binding protein 6

Ultrasound – ultrasonography

UV, UVA – ultraviolet radiation

UVB – ultraviolet type B radiation

Val, V – valine

VDRL – venereal disease research laboratory – preventive examination for syphilis

VEGF – vascular endothelial growth factor

VOC – volatile organic compounds

Wnt – a signaling pathway involved in differentiation, embryogenesis, cell survival and proliferation

XeCl – xenon monochloride (excimer used in lasers excimer)

Zn (zincum) – zinc

ω-3, n-3 – omega-3 acids

ω-6, n-6 – omega-6 acids

ω-9, n-9 – omega-9 acids

1

Anatomy and physiology of skin and hair

There is something good in all the seeming failures. You can’t see it now. Time will reveal it. Be patient.

Swami Sivananda

1.1. Structure and functions of the skin

The skin covers the outer surface of the body and is one of the largest human organs. The skin includes lymphatic vessels, blood vessels, nerve endings and appendages such as sebaceous and sweats glands, nails and hair. Cutaneous vessels which include the venous, arterial and lymphatic systems are responsible for the removal of extracellular fluid. Moreover, the skin consists of three layers: epidermis, dermis and subcutaneous tissue. There are two vascular plexuses, including the deep arterial plexus (located on the border of the subcutaneous tissue and the dermis) and the superficial arterial plexus – subpapillary plexus. The skin is rich in numerous lymphatic vessels, making it an important part of the immune system. Chapter 1 discusses the individual structures of the epidermal layers, embryology and histology of human skin.

Figure 1.1.

Diagram of the structure of the skin divided into epidermis, dermis and subcutaneous tissue

Source: Nowicka D.: Dermatology. Górnicki Medical Publishing House Wrocław 2001, 1–7 and based on the publication: Wolski T., Kędzia B.: Skin pharmacotherapy. Vol. 1, Structure and physiology of the skin. Advances in Phytotherapy, 2019, 1

The skin and all associated structures can be divided according to:

• the molecular level – synthesis of vitamin D precursor, melanin (produced by cells – melanocytes), synthesis of collagen (fibrillar collagen) and elastin, and keratin, i.e. a group of fibrous proteins;

• cellular level – epidermal cells (keratinocytes), connective tissue cells located in the dermis (fibroblasts, involved in the process of elastogenesis), cells of the immune system (including mast cells, lymphocytes and histiocytes), Langerhans cells, skin stem cells, corneocytes (cornified epidermal cells located important in the stratum corneum) and Merkel cells;

• tissue level – epithelial tissue (which makes up the epidermis), as well as connective tissue (which makes up the dermis) and subcutaneous tissue;

• organ level – skin and its appendages – hair, nails and glands.

1.1.1. Epidermis

The epidermis is a multi-layered, constantly renewed thanks to cell proliferation cycles, flat layer of epithelium consisting of dendritic cells and keratinocytes – epithelial cells constituting a significant part of epidermal cells.

Keratinocytes are formed as a result of mitosis of stem cells, produce immunosuppressive cytokines (intensifying the synthesis of prostaglandins – TNF-α) and immunostimulatory cytokines (interleukin 1 – IL-1, interleukin 6 – IL-6, interleukin 8 – IL-8), as well as keratin and defensins. In addition, the epidermis also consists of many other cell populations, such as Langerhans cells – dendritic cells of the immune system of mesenchematic origin, Merkel cells – specific endocrine sensory receptors, or melanocytes, i.e. pigment cells with cytoplasmic processes (vesicles). The epidermis also has a small percentage of lymphocytes located in the basal layer, which has been confirmed in numerous conducted studies using flow cytometry, as well as Toker cells.

Epidermal cells are arranged in overlapping layers. The epidermis consists of (going from bottom to top) the basal layer, the spinous layer, the granular layer, the stratum lucidum and the stratum corneum. Due to the lack of vascularization of the epidermis, its nourishment occurs thanks to the mechanism of diffusion from the dermis.

Langerhans cells

Langerhans cells (LC) are epidermal immune cells of myeloid origin, discovered by Dr. Paul Langerhans in 1868. As indicated in the publication The role of Langerhans cells in pathologies of the skin published by the Journal of the Australian and New Zealand Society for Immunology, these cells perform a regulatory function, suppressing or inducing the disease state. Moreover, they have the ability to produce cytokines – interleukins (e.g. IL-23) or TNF-α. Next, quoting the Encyclopedia Britannica, the most characteristic element of Langerhans cells are Birbeck granules, which are similar in shape to a tennis racket.

Merkel cells

Merkel cells are neuroendocrine in nature (due to the presence of neurosecretory granules in the cytoplasm). These cells originate from the ectoderm of the epidermis. They belong to the group of APUD (Amine Precursor Uptake and Decarboxylation) cells. They were first described by Friedrich Sigmund Merkel in 1875. They are located in the basal layer of the epidermis, in the area of bulding hair and in the oral mucosa. As the Encyclopedia Britannica points out, Merkel cells are cells that receive sensory stimuli, i.e. they function as touch receptors.

Pigment cells

Pigmented cells of nervous origin, melanocytes, are present within the keratinocytes of the basal layer of the epidermis, as well as within the outer epithelial sheath of hair follicles. Melanocytes can also be distinguished in the serous membranes of tissues or in mucous membranes. The pigment produced by melanocytes, i.e. melanin, is transported through cytoplasmic projections to keratinocytes. There are two types of melanin: eumelanin (dark brown) and pheomelanin (pale red/yellowish). The basic function of melanocytes is the ability to produce melanin. The life cycle of melanocytes is composed of differentiation, proliferation, maturation and death of melanocytic cells (in the case of melanocytes contained in hair). Importantly, hormones are responsible for regulating the proliferation of melanocytes, the mechanism of producing melanocytic dendrites and melanogenesis. Intensity of melanogenesis and arrangement of melanocytic processes is determined by racial differences. However, the activity of melanocytes is determined by the cell adhesion of molecules and the paracrine growth factor system mediated by keratinocytes. The intensity of pigmentation and the growth of melanocytes are influenced, among others, by factors secreted by skin fibroblasts, such as neuregulin 1 (a protein from the epidermal growth factors) or stem cell factor influencing hemopoietic stem cells.

1.1.2. Basal cell layer (stratum basale)

The basal (reproductive) layer, also called the columnar cell layer, is the deepest layer of the epidermis, located in the dermis. The round, cylindrical cells found in the basal layer are called cells basal layer. The cells basal layer continually proliferate, producing new cells, resulting in biochemical and morphological differentiation. Importantly, the cells of the basal layer are connected to the basement membrane by hemidesmosomes and to the spinous layer by desmosomes and undergo keratinization, i.e. keratinization of cells. Moreover, in the basal layer there are dendritic pigment cells without desmosomes – melanocytes. Membrane-covered vesicles – melanosomes – synthesize, and then store melanin.

There are two types of melanosomes: eumelanosomes, the mechanism of which synthesizes black-brown eumelanin with a photoprotective effect (mainly against UVB radiation) and pheomelanosomes, which synthesize red-yellow pheomelanin and do not have a protective mechanism.

1.1.3. Layer of spiny cells (stratum spinosum)

The spinous layer consists of pseudostratified, polyhedric cells that connect to each other via desmosomes. Moreover, the spaces of the cells of the spinous layer are filled with the mucopolysaccharide-protein desmoalein. The spinous and basal layers are collectively called malpighian layer.

Figure 1.2.

Structure of the basement membrane and epidermis

Source: Jabłońska S., Chorzelski T.: Skin diseases. PZWL Medical Publishing House, Warszawa 2001, 15–28 and based on the publication: Wolski T., Kędzia B.: Skin pharmacotherapy. Vol. 1, Structure and physiology of the skin. Advances in Phytotherapy, 2019, 1