SKIN BARRIER
- Nina Gudeljević
- Feb 3, 2024
- 7 min read
The protective lipid mantle surrounding skin cells in the epidermis in the stratum corneum, or the horny layer, is crucial for maintaining a healthy skin barrier. If the differentiation process is abnormal, irregularities in the skin barrier may occur, associated with compromised skin health and the pathophysiology of certain skin conditions such as xerosis, ichthyosis, atopic dermatitis, psoriasis...
The key process of the epidermal barrier is controlling the diffusion of molecules through the skin, including transepidermal water loss from inside to outside and the penetration of chemicals from the outside to the inside.
Diffusion can occur in two ways:
Intracellularly through the lipid matrix of the epidermis.
Transcellularly across corneocytes.
The rate of diffusion depends on:
The unique lamellar organization of the lipid matrix and its interaction with protein components of keratinocytes, including tight junctions and proteins.
The diffusion path length, determined by the thickness of the stratum corneum, the number of layers of corneocytes, their size, and cohesion.
The skin barrier is divided into four types: physical, chemical, biochemical, and immunological barriers.
It influences not only simple barrier functions but also the structure and roles of living cell layers in the epidermis and dermis.
Epidermal corneocytes form the skin barrier through proliferation, differentiation, a type of apoptosis (cell death), and eventually undergo desquamation or shedding of dead skin cells.
The function of the epidermal skin barrier enables normal biochemical metabolic processes and protects the skin from drying and external harmful factors. Its role is to retain moisture in the skin, prevent the penetration of microbes, allergens, and irritating substances, and protect against UV rays.
When the skin barrier is damaged, maintenance of homeostasis occurs, such as lipid secretion and synthesis. The use of an external ointment containing intercellular lipid components is known to restore the skin barrier. An effective moisturizer must have the right balance of components such as cholesterol, ceramides, and fatty acids, which are integral to the skin barrier.
The most significant benefit cosmetic products can offer is a moisturizing effect. A physiological mixture of lipids can be considered the most ideal moisturizer, reinforcing the lipid barrier function to regulate the moisture content in the stratum corneum.
Skin moisturizing is closely related to the moisture content of the stratum corneum. Decreased moisture content can lead to skin dryness and abnormalities in the skin barrier function. Therefore, maintaining moisture in the stratum corneum is crucial for preventing moisture loss in intercellular lipid. Moisturizers help in the smooth execution of metabolic activity in the stratum corneum.
If the skin barrier is damaged, it results in the evaporation of moisture from the skin, making it easier for microbes, allergens, and cosmetic ingredients (including toxic ones) to penetrate the skin and potentially increase side effects.
Factors that can cause damage to the skin barrier include:
chlorine in pools
water containing excessive calcium, magnesium, chlorine, salts, and the use of water at inappropriate temperatures
aggressive personal care products and improper use of cosmetic products
excessive use of exfoliants
use of cholesterol-lowering medications
friction on the skin
overexposure to sunlight
unhealthy diet and beverages
stress
lack of sleep
alcohol and smoking.
When the skin barrier is compromised, it may manifest as dehydration, infections, rashes, inflammatory changes, allergies, irritations, excessive desquamation or peeling, and heightened sensitivity. Dry, dull, rough-to-touch, itchy skin, accompanied by a feeling of tightness soon after cleansing, are common signs. Applying moisturizers and lipids provides relief as the skin receives essential nutrients and moisture.
BIOCHEMISTRY OF SKIN WITH BARRIER FUNCTIONS:
pH: The skin has a normal pH between 4.5 and 5.5, and acidity is crucial for maintaining the skin barrier. Enzymes in the stratum corneum, including beta-glucocerebrosidase and acid sphingomyelinase, function well in acidic environments and are responsible for producing ceramides and free fatty acids that influence diffusion through the epidermis. The acidic surface of the skin, along with the stratum corneum, prevents the penetration of microbes and supports normal skin microbiota.
Filaggrin: Filaggrin is a specialized structural protein responsible for the structural and mechanical integrity of the stratum corneum. It stores keratin filaments inside corneocytes and helps form the cornified cell envelope outside corneocytes. Natural moisturizing factors, degradation products of filaggrin, contribute to water retention ability and the acidic pH of the stratum corneum. Urocanic acid, another breakdown product of filaggrin, is essential for protection against UV radiation damage.
Melanin: Melanosomes, which contain melanin, are produced in melanocytes in the basal membrane of the epidermis and stored in melanosomes. Melanosomes travel to keratinocytes, protecting the nucleus of epidermal cells against DNA damage from UV radiation.
Antimicrobial Peptides: Synthesized in the skin by keratinocytes, sebocytes, and sweat glands, antimicrobial peptides have antimicrobial and immunomodulatory effects.
Immune Cells: Numerous immune cell types, such as dermal dendritic cells, mast cells, and lymphocytes (T cells, B cells, NK cells), are located in the dermis.
Certain nutrients and vitamins are crucial for maintaining a healthy skin barrier, including vitamins A, B3 (nicotinamide), B7 (biotin), and D
Vitamin A: This fat-soluble vitamin is essential for skin health. It supports cell turnover and helps maintain the integrity of the skin barrier.
Vitamin B3 (Nicotinamide): Also known as niacinamide, this water-soluble vitamin has anti-inflammatory properties and helps in maintaining the skin barrier. It is involved in cellular energy production and can contribute to a healthy complexion.
Vitamin B7 (Biotin): Biotin is important for skin health as it plays a role in the metabolism of fatty acids, which are integral components of the skin barrier.
Vitamin D: This fat-soluble vitamin is essential for overall health, and it also contributes to skin health. It plays a role in skin cell growth, repair, and immune function.
Ensuring an adequate intake of these vitamins through a balanced diet or supplements, if necessary, can support the maintenance of a healthy skin barrier.
KOŽNA BARIERA
Je zaščitni plašč lipidov, ki obdaja celice kože v epidermisu v stratum corneum ali roževinasti plasti – če je proces diferenciacije abnormalen, se pojavijo nepravilnosti v kožni barieri – povezana je z deterioriacijo zdravja kože in patofiziologijo nekaterih kožnih bolezni, kot so kseroza, ihtioza, atopičen dermatitis, psoriaza…
Ključni proces bariere epidermisa je nadzorovanje difuzije molekul skozi kožo – transepidermalna izguba vode, od znotraj navzven ter kemikalij od zunaj navznoter
Difuzija lahko poteka na 2 načina:
· znotrajcelično skozi lipidni matriks epidermisa
· transcelično skozi korneocite
Hitrost difuzije je odvisna od:
· edinstvene laminarne organizacije lipidnega matriksa in njenega delovanja s proteinskimi komponentami keratinocitov, vključno s tesnimi spoji in proteini
· dolžina difuzijske poti, ki jo določa debelina roževinaste plasti, število plasti korneocitov, njihova velikost in kohezija
Razdeljena je v 4 tipe: fizična, kemična, biokemična in imunološka bariera – ima vpliv na preproste barierne funkcije, na strukturo in vlogo v živih celicah epidermisa in dermisa
Epidermalni korneociti tvorijo kožno bariero skozi proliferacijo, diferenciacijo in neko vrsto apoptoze (celična smrt) in na koncu gredo skozi proces deskvamacije ali lušenje odmrlih celic kože.
* funkcija kožne pregrade epidermisa omogoča normalne biokemične presnovne procese ter ščiti kožo pred izsuševanjem in zunanjimi škodljivimi dejavniki à
à njena funkcija je, da zadrži vlago v koži, prepreči vdor mikrobov, alergenov in sestavin, ki dražijo kožo, varuje pred UV žarki
kadar je kožna bariera poškodovana, se izvaja vzdrževanje homeostaze, kot je izločanje in sinteza lipidov – znano je, da se uporaba zunanjega mazila, ki vsebuje medcelično lipidno komponento potem kožna bariera tudi obnovi – biti mora vlažilec s pravim razmerjem komponent, kot so holesterol, ceramidi, maščobne kisline, ki so tako in tako del kožne bariere
največja korist, ki jo lahko kozmetični izdelki ponudijo, je vlažilni učinek – fiziološka mešanica lipidov se lahko šteje za najbolj idealen vlažilec – okrepi funkcijo lipidne pregrade za prilagajanje vsebnosti vlage v roževinasti plasti in medcelična lipidna komponenta izpolnjuje to funkcijo
vlaženje kože je tesno povezano z vsebnostjo vlage v roževinasti plasti. Zmanjšanje vsebnosti vlage lahko povzroči suhost kože in nenormalnosti v funkciji kožne bariere – zato je zelo pomembno vzdrževanje vlage v roževinasti plasti, ki je pogoj za preprečevanje izgube vlage na medcelični lipid – vlažilec pomaga pri gladkem izvajanju presnovne aktivnosti v roževinasti plasti
če je kožna bariera poškodovana, to povzroča izhlapevanje vlage iz kože, mikrobi in alergeni lažje vdrejo v notranjost, kozmetične sestavine lažje prodrejo v kožo (tudi tiste, ki so toksične) in lahko povečajo stranske učinke
Kaj pa lahko povzroča poškodbo kožne bariere?
Ø klor, ki se nahaja v bazenih
Ø voda, ki vsebuje preveč kalcija, magnezija, klora, soli in uporaba neustrezne temperature vode
Ø agresivne PAS in napačna nega kože oz. neustrezna uporaba kozmetičnih produktov
Ø pretirana uporaba pilingov
Ø uporaba zdravil, ki znižujejo holesterol
Ø drgnjenje kože
Ø prevelika izpostavljenost soncu
Ø nezdrava prehrana in pijača
Ø stres
Ø pomanjkanje spanca
Ø alkohol in kajenje
Kadar imamo poškodovano kožno bariero, se to lahko pokaže v obliki dehidracije, infekcij, izpuščajev, vnetnih sprememb, alergij, iritacij in zbadanj, pretirana deskvamacija ali luščenje, koža zelo hitro reagira, pojavijo se ekcemi in postane zelo občutljiva.
Takšna koža je ponavadi suha, pusta, groba na dotik, srbeča, pojavi se občutek zategovanja kmalu po tem, ko se koža očisti in ko se nanese vlažilce in lipide, nastane občutek olajšanja, saj je koža dobila vsa svoja hranila in vlago.
BIOKEMIJA KOŽE Z BARIERNIMI FUNKCIJAMI:
pH: koža ima normalen pH med 4,5 – 5,5 in kislost je pomembna pri ohranjanju kožne bariere. Encimi v stratum corneum, vključno z beta-glukocereberosidaza in kislinska sfingomielinaza, funkcionirajo lahko v kislem okolju in so odgovorni za proizvodnjo ceramidov in prostih maščobnih kislin, ki vplivaj na difuznost skozi epidermis. Kisla površina kože skupaj z stratum corneum preprečujejo vdor mikrobov in podpirajo normalno mikrobiomo kože
filagrin: je specializirana strukturna beljakovina, odgovorna za strukturno in mehansko integriteto stratum corneum (roževinasta plast). Shranjuje keratinske filamentne znotraj roževinskih celic in pomaga oblikovati roževinski ovoj celic zunaj roževinskih celic. Naravni vlažilni faktorji so razgradni produkti filagrina, ki prispevajo k sposobnosti zadrževanja vode in kislega pH roženice. Urokaninska kislina, drugi razgradni produkt filagrina, je pomembna pri zaščiti pred poškodbami zaradi UV sevanja.
melanin: je pigment, ki se proizvaja v melnocitih v bazalni membrani epidermisa in je shranjen v melanosomih. Melanosomi potujejo proti keratonicitom, ki varujejo jedro epidermalne celice pred poškodbami DNA zaradi UV sevanja.
protimikrobni peptidi: so sintetizirani iz strani keratinocitov, lojnic in žlez znojnic v koži, imajo protimikrobne in imunomodulatorne učinke.
kožni dodatki, ki imajo tudi vlogo pri zaščiti kožne bariere: ključne imunske celice v epidermisu so keratinociti in Langerhalsove celice – številne imunske celice se nahajajo v dermisu in vključujejo dendritične celice, mastocite in limfocite (celice T, celice B, NK-celice)
tudi določena hranila in vitamini so pomembni za ohranjanje zdrave kožne bariere – vitamini A, B3 (nicotinamid), B7 (biotin), D.
VIRI:
*Hyun Hee Jang, Sung Nae Lee, School of Cosmetology, Kyungbok University, Epidermal Skin Barrier, Asian J Beauty Cosmetol; 14(3): 339-347
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