Healthy skin is a powerful shield, protecting our inner organs from external threats. Recent advances in Corneobiology have revealed that the skin’s outermost layer, the Stratum Corneum, plays a crucial role in this defence by functioning as multiple barriers, including:
Permeability Barrier
Antimicrobial Barrier
Antioxidant Barrier
Immunity Barrier
Photoprotection Barrier
These natural defences help the skin resist threats such as UV rays, pollutants, and harmful microorganisms. However, both external and genetic factors can weaken these barriers, leading to various skin disorders.
The Impact of External Threats and Genetics on Skin Health
Our skin is constantly exposed to external factors like UV rays, pollutants, chemicals, and microbes, all of which can weaken its defences. When healthy, the Stratum Corneum’s barrier systems can usually handle these threats. However, internal factors such as hereditary disorders or gene mutations can also affect barrier strength. This combination of external and internal factors can lead to complex skin conditions, such as:
Atopic dermatitis (eczema)
Rosacea
Psoriasis
Acne vulgaris
While these conditions are often managed with treatments like corticosteroids or retinoids, research suggests that such treatments might actually harm the skin’s natural defences. [2]
How Skin’s Structural Components Work with Its Barriers
The skin’s structure also plays a defensive role. Components like the Acid Mantle, Microbiome, Corneocytes, and Multilamellar Lipids work in harmony with the permeability, antimicrobial, and other barrier systems to keep us protected. Let’s dive deeper into one of these essential barriers, the Permeability Barrier.
The Permeability Barrier: A Key Protector
The Permeability Barrier is largely managed by the Stratum Corneum. Its structure resembles a "brick and mortar" wall, where Corneocytes are the bricks and Multilamellar Lipids (fat molecules) are the mortar. These lipids include Ceramides, Cholesterol, and Fatty Acids, which repel water-soluble (hydrophilic) invaders. This keeps harmful substances from entering the body.
Let’s discuss these Barrier Lipids in more depth to really understand how they maintain the integrity of the Permeability Barrier.
Understanding Barrier Lipids
These Multilamellar Lipids are arranged in a unique crystalline structure. If this structure is disrupted by factors like PUFA deficiency or the use of alkaline soaps, the barrier can break down. This leads to Trans-Epidermal Water Loss (TEWL) and makes the skin vulnerable to invaders. [2]
The Role of Polyunsaturated Fatty Acids (PUFAs)
PUFAs (like Omega-6 and Omega-3) are essential for maintaining the barrier lipids. A deficiency can result in the degradation of the barrier, leading to conditions like dry skin (Xerosis). Omega-6, in particular, forms Ceramide 1 Linoleate, a crucial part of the skin’s defence. Without it, the skin substitutes less effective lipids, compromising the barrier’s integrity. [3,4]
More on PUFAs
To better appreciate PUFAs we should backup a bit and mention the three (3) major classes of nutrients generally required by our body to carry out everyday chores, these are: 1. Carbohydrates; 2. Proteins; 3. Lipids and are known collectively as Macronutrients or ‘macros’. However, there are some chores that require specially outsourced tools that the body can only obtain from particular foods. This special group is referred to as Polyunsaturated Fatty Acids (PUFAs) and is a subclass of the Lipid family. PUFAs take care of a range of things in our body, from blood clotting to muscle movement, lowering bad cholesterol to postponing heart disease and stroke. As you can see, there is a reason why ‘essential’ is tagged onto these neat fatty acids. Say hello to Omega 6 (Linoleic acid & Arachidonic acid) and Omega 3 (Alpha-linolenic acid [ALA], Eicosapentaenoic acid [EPA] & Docosahexaenoic acid [DHA]). These are mainly found in fish, nuts and seeds— foods that are the hallmark of the Mediterranean Diet. You might have also heard about Omega 9 (oleic acid); well, here’s a bit of a twist Oleic acid is a Monounsaturated Fatty Acid, which is important as well, but more so in Hair Care Science. The World Congress of Dermatology, which hosts annual symposiums addressing common skin conditions, suggest that Essential Fatty Acid Deficiency (EFAD) specifically affects Barrier Lipids of Stratum Corneum.[5]
The quantity and quality of Ceramides often depends on Omegas 3 and 6.
The skin has intelligent mechanisms in place that help prevent the collapse of the lipid lamellae. Such mechanisms are mediated by modulatory complexes called Lipid Phase Modulators, namely Ceramide 1 & 3. Ceramides are sphingolipids that are essential not only as phase modulators but in helping trap and retain moisture. Ceramide 1 often binds with Linoleic acid (Omega 6) to yield a more stable and effective phase modulator known as Ceramide 1 Linoleate. Deficiencies in PUFAs, in this case Omega 6, single-handedly is responsible for the absence of the guardian Ceramide 1 Linoleate, which in turn results in the collapse of the crystalline structure and loss of Permeability Barrier integrity. Scientists have discovered that in Essential Fatty Acid Deficiencies (EFADs), the Ceramide-1 lipid compound senses the urgency of things and frantically grabs onto the nearest fatty acid substitute, most commonly Omega 9 (Oleic acid), complexing with it to form the less than ideal counterpart, Ceramide 1 Oleate— a compound observed at elevated levels in Dry Skin (Xerosis). [3-7]
Corneocytes: The Skin’s Cellular Defense
Corneocytes, the cells that make up the Stratum Corneum, play a key role in protecting the skin. They connect tightly with each other and form a strong, compact layer. If these connections are weak, pathogens can penetrate deeper into the skin, causing inflammatory responses and contributing to conditions like Ichthyosis or Rosacea.
Additionally, Tight Junctions between Corneocytes prevent the entry of foreign matter, and their Cornified Cell Envelopes (CE) support the deposition of protective lipids. Poorly formed CE structures can lead to an imbalance in the skin's microbiota, allowing harmful bacteria like Staphylococcus aureus to thrive.
The Skin’s Antimicrobial & Immune Barriers
The skin is home to many beneficial microbes that work as a defence system. These microbes, including Staphylococcus epidermidis, produce Antimicrobial Peptides (AMPs) to fight off harmful bacteria. In addition to producing AMPs, Corneocytes can detect and respond to threats by activating the Innate Immune System.
If the Cornified Cell Envelopes or Lipid Layers are compromised, this early immune response is weakened, leaving the skin vulnerable to pathogens. The Langerhans cells, found in deeper layers of the skin, play a crucial role by activating the Adaptive Immune System when needed, ensuring long-term defence.
The Antioxidant Barrier: Protection Against Oxidative Stress
The Stratum Corneum is constantly exposed to oxidative stress from environmental factors like UV radiation and air pollutants. Fortunately, the skin’s Antioxidant Barrier is equipped to neutralize harmful free radicals. These antioxidants include both enzymatic (e.g., Superoxide Dismutase) and non-enzymatic (e.g., Vitamins E & C) systems.
When these antioxidant systems are overwhelmed, the skin’s DNA, lipids, and proteins can be damaged, accelerating the ageing process. Eustress (beneficial stress, like exercise) can help boost the skin’s defence mechanisms, while a combination of oral and topical antioxidants further strengthens this barrier. [10-11]
Melatonin, one of the non-enzymatic antioxidants, has been shown scientifically to promote Longevity and is a hormone produced by our Pineal Gland or “Third Eye”.
The Photoprotection Barrier: Defending Against UV Rays
The Melanin Barrier, or Photoprotection Barrier, protects the skin from harmful UV radiation (UVR). There are three types of UV rays:
UVC: Mostly blocked by the ozone layer.
UVB: Penetrates the epidermis and causes sunburn.
UVA: Penetrates deeper and can lead to DNA damage.
Melanin, produced by Melanocytes, absorbs UV rays, protecting the skin from photo-oxidative stress and DNA mutations that can lead to conditions like Melanoma. Melanin pigment comes in two variants, Eumelanin and Pheomelanin, with the first variant being the more imminent player with good free radical scavenging abilities; in contrast to the latter variant (pheomelanin) being more unstable by nature, often spontaneously generating reactive oxygen species that increase skin’s sensitivity to light (Photosensitization) and induce the development of skin diseases like Melanoma.Hyperpigmentation, also known as skin tanning, is a prominent reaction to intense sunlight that increases the presence of eumelanin in the skin. [1]
More on UVR
There are three major UV rays: UVC, UVB and UVA. The first, UVC (100nm-280nm), is the most damaging ray on the ultraviolet spectrum which mostly gets trapped, thankfully, by the Ozone Layer. UVB (280nm-315nm) is able to penetrate the ozone as well as all of the epidermal layers, down to Stratum Basale. The visible evidence of UVB’s effects on the skin manifests as Sunburns (Solar Erythema). Finally, UVA (315nm-400nm) is able to penetrate the ozone layer, the epidermis, all the way to the Dermis. This ultraviolet long wave is known to cause damage to DNA (UV Mutagenesis) resulting in skin diseases like Melanoma. Besides harmful frequencies like UVR on the electromagnetic spectrum, skin scientists suggest that other light waves, like ones on the Visible Light Spectrum (400nm-700nm), also generate Free Radicals in contact with skin. Thankfully, Stratum Corneum is equipped with Photoprotective features that attenuate these distant rays either by: Scattering (reflection/deflection); Absorption; or through DNA protective mechanisms that shield our genetic information.
Optical Reflection is the physical property of some materials to reflect light waves, Stratum Corneum’s physical structure is capable of this and is dependent on the thickness and cell compaction of this stratum and the rest of the viable epidermis. Attenuation of radiation is largely contributed to Absorption by specialized light-trapping compounds called Chromophores. These compounds have optical absorbances at the level of S. Corneum and the other layers of the epidermis. Urocanic Acid is a popular chromophore that has good overall wavelength absorbance but absorbs optimally around 277nm. Peptide bonds also absorb light waves, with maximal absorbance around 240nm. Melanin, commonly considered the Endogenous Sunscreen, is a pigment produced by Melanocytes and stored in Melanosomes that has broad but variable absorbance between 250nm-1,200nm but works best on shorter waves. [1,12 ] Lastly, DNA protective mechanisms, which are made possible by the clustering of melanosomes over a keratinocyte’s nuclear envelope, physically shield DNA from mutagenic radiation. Melanosomes containing melanin get transported along the tentacle-like arms of melanocytes, eventually getting transferred to surrounding keratinocytes.
All in all, Skin’s Barrier Defence features (Permeability Barrier, Antimicrobial Barrier, Antioxidant Barrier, Immunity Barrier & Photoprotection Barrier) come together synergistically to help retain and restore skin health in the most beautiful and elegant way. When the skin’s defences are insufficient, well-formulated barrier-promoting Skin Care Products are great supplementary aids in complementing the skin’s barrier defence mechanisms. In fact, Corneotherapy, the subfield of Dermatology concerned with the repair and retention of skin’s barrier integrity, particularly at the Stratum Corneum level, is pioneering novel approaches that some cosmetic formulators are adopting. Indeed, Corneotherapeutic principles applied to well-formulated, Plant-Based Skin Care Products might be by far our best bet for healthy, youthful skin.
Samuel M.T Jones
Bsc. Biological Sciences (Hons.)
PG. Dip. Organic Personal Care/Cosmetic Science
PG. Cert. Barrier Disordered Skin
PG. Cert. Beekeeping
References
1. Lefèvre-Utile A, Braun C, Haftek M, Aubin F. Five Functional Aspects of the Epidermal Barrier. Int J Mol Sci [Internet]. 2021 Oct 28 [cited 2022 November];22(21):11676. Available from: https://pubmed.ncbi.nlm.nih.gov/34769105/
2. Del Rosso J, Levin J. The clinical relevance of maintaining the functional integrity of the stratum corneum in both healthy and disease-affected skin. J Clin Aesthet Dermatol [Internet]. 2011 Sep [cited 2022 July];4(9):22-42. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3175800/
3. Vávrová K, Kováčik A, Opálka L. Ceramides in the skin barrier. Eur. Pharm. J [Internet]. 2017 Jan [cited 2022 May 5];64 (1):1-8. Available from: https://www.researchgate.net/publication/318401653_Ceramides_in_the_skin_barrier
4. Mijaljica D, Spada F, Harrison I. Skin Cleansing without or with Compromise: Soaps and Syndets. Molecules [Internet]. 2022 Mar 21 [cited 2022 November];27(6):2010. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8954092/
5. Zouboulis CC, Herane MI, Thiboutot DM. Acne symposium at the world congress of dermatology. Dermatology. [Internet]. Basel, Switzerland: Karger; 2003 [cited 2022 April 28] 74p. Available from: https://www.karger.com/Book/Home/228914
6. Janssens M, van Smeden J, Gooris GS, Bras W, et al. Increase in short-chain ceramides correlates with an altered lipid organization and decreased barrier function in atopic eczema patients. J Lipid Res [Internet]. 2012 Dec [cited 2022 May 3];53(12):2755-66. Available from: https://pubmed.ncbi.nlm.nih.gov/23024286/
7. Petra P, Elena E, Andrej K, Lukáš O, et al. Long and very long lamellar phases in model stratum corneum lipid membranes. J. Lipid Res [Internet]. 2019 May [cited 2022 May 3];60(5):963-971. Available from: https://www.sciencedirect.com/science/article/pii/S0022227520322665
8. Nguyen HLT, Trujillo-Paez JV, Umehara Y, et al. Role of Antimicrobial Peptides in Skin Barrier Repair in Individuals with Atopic Dermatitis. Int J Mol Sci [internet]. 2020 Oct [cited 2022 October];14;21(20):7607. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7589391/
9. Zheng Y, Hunt LR, Villarus EA, et al. Commensal Staphylococcus epidermidis contributes to skin barrier homeostasis by generating protective ceramides. Cell Host & Microbe [Internet]. 2022 March [cited 2022 October];30(3),301-313.e9. Available from: https://www.cell.com/cell-host-microbe/pdf/S1931-3128(22)00040-3.pdf
10. Addor FAS. Antioxidants in dermatology. An Bras Dermatol [internet]. 2017 May-Jun [cited 2022 October];92(3):356-362. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5514576/
11. Ristow M, Schmeisser S. Extending Life Span by Increasing Oxidative Stress. Free Radic. Biol. Med [Internet]. 2011 July [cited 2022 October];51(2):327-336. Available from: https://www.sciencedirect.com/science/article/pii/S0891584911003121?via%3Dihub
12. Anderson R, Parrish J. The Optics of Human Skin. J. Invest. Dermatol. [Internet]. 1998 July [cited 2022 November 5];77(1):13-19. Available from: https://www.sciencedirect.com/science/article/pii/S0022202X15461251?ref=cra_js_challenge&fr=RR-1
13. Ross M, Pawlina W. Histology: A Text and Atlas. 7th ed. Philadelphia: Lippincott, Williams & Wilkins; Jan 2015. 496p
14. de Araújo R, Lôbo M, Trindade K, Silva D, F, Pereira N: Fibroblast Growth Factors: A Controlling Mechanism of Skin Aging. Skin Pharmacol Physiol [Internet]. 2019 August [cited 2022 August 6];4:275-282. Available from: https://www.karger.com/Article/Fulltext/501145#
15. Harding CR, Watkinson A, Rawlings AV, Scott IR. Dry skin, moisturization and corneodesmolysis. Int J Cosmet Sci [Internet]. 2000 Feb [cited 2022 April 28];22(1):21-52. Available from: https://pubmed.ncbi.nlm.nih.gov/18503460/
16. Rainer B, Kang S, Chien A. Rosacea: Epidemiology, pathogenesis, and treatment. Dermatoendocrinol [Internet]. 2017 Oct 4 [cited 2022 August]; 9(1):e1361574. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5821167/
17. Schwab D, Sulk M, Seeliger S, Nowak P, et al. Neurovascular and neuroimmune aspects in the pathophysiology of rosacea. J Investig Dermatol Symp Proc [Internet]. 2011 Dec; [cited 2022 August] 15(1):53-62. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3704331/
18. Cancer: Radiation and Cancer Risk [Internet]. UV Radiation. Revised 2019 July 10 [Cited 2022 May 5]. Available from: https://www.cancer.org/cancer/cancer-causes/radiation-exposure/uv-radiation.html
19. Wong DJ, Chang HY. Skin tissue engineering. 2009 Mar 31. StemBook [Internet]. Cambridge (MA): Harvard Stem Cell Institute; 2008. Available from: https://www.ncbi.nlm.nih.gov/books/NBK27029/figure/skintissueengineering.F1/ doi: 10.3824/stembook.1.44.1
20. Harvard Health Publishing [Internet]. The truth about fats: the good, bad, and the in-between; 2022 April 22 [cited 2022 May]. Available from: https://www.health.harvard.edu/staying-healthy/the-truth-about-fats-bad-and-good
21. Oncobeta: Epidermal Radioisotope Therapy [Internet]. The Skin. [Cited 2022 May 5]. Available from: https://www.oncobeta.com/your-health/nmsc-info/the-skin
22. Heart: Fats [Internet]. Polyunsaturated Fats; Revised 2015 Jun 1 [cited 2022 May 5]. Available from: https://www.heart.org/en/healthy-living/healthy-eating/eat-smart/fats/polyunsaturated-fats
23. Formula Botanica [Internet]. 5 Natural surfactants for use in organic cosmetics. [Cited 2022 May 5]. Available from: https://formulabotanica.com/natural-surfactants/
24. Kaur N, Chugh V, Gupta AK. Essential fatty acids as functional components of foods- a review. J Food Sci Technol. [Internet]. 2014 Oct [cited 2022 May 3];51(10):2289-303. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4190204/
25. Rendon A, Schäkel K. Psoriasis Pathogenesis and Treatment. Int J Mol Sci [Internet]. 2019 Mar 23; [cited 2022 August] 20(6):1475. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6471628/
26. Elias P. Skin barrier function. Curr Allergy Asthma Rep [Internet]. 2008 Jul; [cited 2022 August] 8(4):299-305. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2843412/
27. Le Lamer M, Pellerin L, Reynier M, et al. Defects of corneocyte structural proteins and epidermal barrier in atopic dermatitis. Biological Chemistry [Internet]. 2015; [cited 2022 August] 396(11): 1163-1179. Available from: https://www.degruyter.com/document/doi/10.1515/hsz-2015-0141/html?lang=en#Vancouver
コメント