The Structures & Functions of the Skin
The skin is the largest and arguably the most important organ of our body, divided into several layers it accounts for approximately 15% of our total body weight. The three primary layers of the skin are the epidermis, dermis and subcutaneous layer (hypodermis). Each layer is composed of certain cells and structures which contribute to the skin’s overall appearance, structure, and function.
THE SKIN HAS FIVE MAIN FUNCTIONS:
Protection
1. Harmful Agents.
2. Excessive loss of moisture and protein.
3. Mechanical, thermal and other physical injury.
4. Harmful effects of UV radiation.
Thermoregulation
One of the skin’s important functions is to protect the body from cold or heat, and maintain a constant core temperature. The secretion and evaporation of sweat from the surface of the skin also helps to cool the body.
Sensation
Skin is the ‘sense-of-touch’ organ that triggers a response if we touch or feel something, including things that may cause pain as well as pleasure.
Immune Defense
The skin is an important immunological organ, made up of complex key structures and cells. Depending on the immunological response, a variety of cells and chemical messengers (cytokines) can be activated and function to protect the body.
Biochemical Functions
The skin is involved in several biochemical processes. For example, in the presence of sunlight, vitamin D is synthesized, which is essential for the normal absorption of calcium and phosphorus (required for healthy bones).
Epidermis: The Outer Layer
Dermis: The Middle Layer
Hypodermis: The Fatty Layer
Epidermis: The Outer Layer
Though the epidermis is the thinnest layer of the skin, the prime function of this layer is to act as a physical and biological barrier to the external environment, preventing penetration by irritants and allergens. At the same time, it prevents the loss of water and maintains internal homeostasis. The epidermis is composed of layers; most areas of the skin have four layers, but those areas with the thickest skin have five. The layers are:
- • Stratum corneum
- • Stratum lucidum
- • Stratum granulosum
- • Stratum spinosum
- • Stratum basale
The epidermis also contains other cell structures, keratinocytes, melanocytes, Lengerhans cells, as well as Merkel cells.
- • Keratinocytes - produce the protein keratin (the main component of the epidermis), these cells make up around 95% of the epidermal cell population and are formed by division in the stratum basale.
- • Melanocytes - specialised cells found in the stratum basale scattered among keratinocytes along the basement membrane, which produce skin pigment; also known as melanin. Melanin has the main function of absorbing UV radiation, protecting us from its harmful effects.
- • Melanosomes - (both present in melanocytes and keratinocytes) are the melanin producing organelles that are responsible for the pigmentation of the hair and skin.
- • Langerhans cells - help to prevent external matter from penetrating into your skin.
- • Merkel cells - specialised cells found right beneath the epidermis. These cells are very close to the nerve endings that receive the sensation of touch and may be involved in the body's sensory perception.
Skin colour is influenced by a multitude of factors. The spectrum of colour is determined by cells in the epidermis called melanocytes. Within these cells are organelles (melanosomes), the factory houses for the production of the brown/red pigment called melanin. Once melanin is produced, these organelles are then transported to the more superficial cells of the epidermis (keratinocytes). The purpose of melanin, as well as giving skin its colour, is to protect and shield the skin cells from Ultraviolet light – both UVA and UVB. When there is an increase in UV radiation, both the production and the distribution of melanin increase accordingly.
Difference in skin colour is not only determined by the quantity of melanocytes, but also, the type of melanin produced, the size of the melanosome, the amount of melanin in each melanosome as well as their distribution throughout the epidermis. It is also influenced by genetic factors, hormones, and even by pigments including melanin, carotene as well as haemoglobin.
Fact: Studies have shown that individuals living in densely populated urban areas or cities with high levels of airborne pollutants are more prone to premature ageing, hyperpigmentation as well as other skin irritations. It is thus important to keep the outer skin cleansed and hydrated with various naturally occurring nutrients, and of course, avoid excessive sun exposure which can damage the skin as well.
Langerhans Cells - These are antigen (microorganisms and foreign proteins) presenting cells found in the stratum spinosum. They are part of the body’s immune system, activating various immune responses.
Merkel Cells - These cells are only present in very small numbers in the stratum basale. They seem to have a role in sensation, especially in areas with a higher level of sensitivity.
Dermis: The Middle Layer
The dermis forms the inner layer of the skin and is much thicker than the epidermis. Situated between the basement membrane zone and the subcutaneous layer, the primary role of the dermis is to sustain and support the epidermis. The main functions of the dermis are:
- Protection.
- Cushioning the deeper structures from mechanical injury.
- Providing nourishment to the epidermis.
- Playing an important role in wound healing.
The papillary dermis is the thinner layer, consisting of loose connective tissue containing capillaries, elastic fibres and some collagen. The reticular dermis consists of a thicker layer of dense connective tissue containing larger blood vessels, closely interlaced elastic fibres and thicker bundles of collagen. It also contains fibroblasts, mast cells, nerve endings, lymphatics and epidermal appendages. Surrounding these structures is a viscous gel that:
- Allows nutrients, hormones and waste products to pass through the dermis.
- Provides lubrication between the collagen and elastic fibre networks.
- Gives bulk, allowing the dermis to act as a shock absorber.
The fibroblast is the major cell type of the dermis, its main function is to synthesise collagen, elastin and the viscous gel within the dermis. Collagen, which gives the skin its toughness and strength, makes up 70% of the dermis and is continually broken down and replaced, while elastin fibres give the skin its elasticity. Both components are affected by ageing and UV radiation exposure, which results in sagging and stretching of the skin as the person gets older and/or is exposed to greater amounts of UV radiation. Keeping the skin in good condition, avoiding excess sun exposure, following a healthy and balanced lifestyle, using good sun protection, and using nourishing active ingredients in your skincare products can all help to prevent early onset changes in the dermis.
Hypodermis: The Fatty Layer
The hypodermis is the subcutaneous layer lying below the dermis; it consists largely of fat. This layer of fat is the deepest layer of skin, it basically attaches your bones to your muscle and bones. It provides the main structural support for the skin, as well as insulating the body from cold and aiding shock absorption. It is interlaced with blood vessels and nerves.
Skin of Colour: A Historical Perspective
Throughout history, the subject of skin of colour has been covered up in multiple, complex layers of misconception, mystique, and misunderstanding. Since antiquity, people have sought answers to various questions, such as, “where does skin colour come from?”, “what was the skin colour of the first human”, and “why do people develop different skin colours?”. Naturally, ancient people sought to answer these questions through mythology, one of the earliest explanations for skin colour was proposed by the ancient Greeks. Early African mythology also produced a theory, there are various North American Indigenous legends and of course, every religion seems to have its own
doctrine on the origin of skin colour; especially on the source of darker vs. lighter tones.
Although history has taken us on a journey in terms of how, why, where and when skin has changed and evolved throughout history, a widely accepted modern theory of skin colour is the vitamin D/sunlight theory. But this too, is merely postulation. With time, knowledge and technology, we have been able to further develop our theories and beliefs; coming to a more scientific and biological explanation of the skin, and why it functions differently according to its shade.
The Science of the Melanin Pigmentary System
Although there has been much philosophical, religious, mythological and even scientific speculation on the causes of skin colour, science and medicine has provided us with the biological answers to these clinical observations.
The skin has epidermal units that are responsible for melanin production and distribution, a process called melanogenesis. These units are composed of a melanocyte surrounded by keratinocytes and regulated by a closed paracrine system. Melanin is the primary determinant of skin, hair, and eye colour. And plays a critical role in photo protection due to its ability to absorb ultraviolet radiation (UVR). The system is the most commonly used system to distinguish different skin pigmentation phenotypes. It characterises six phototypes (I-VI) by grading erythema and acquired pigmentation after exposure to UVR. Constitutive pigmentation reflects the genetically determined level of melanin and can be changed by several regulatory factors. These factors may be intrinsic or extrinsic influences.
Although darker and lighter skin have the same number of melanocytes, individuals with darker skin have a greater number of dendrites, and their melanocytes have greater biological activity compared to those found in lighter toned individuals. In lighter skin, melanosomes are small and grouped together, as a result, there is less visible melanin. Little melanin is contained in the keratinocytes in the superficial layer of the skin (epidermis). In darker skin, melanosomes are larger and contain more melanin which is released and dispersed more uniformly throughout the epidermis, making the skin appear darker.
One of the most recent influences on the concept of ethnic background and skin colour are the findings from the HGP (Human Genome Project), which began in 1990, a scientific and biological mission to understand the genetic makeup of people. The study of human skin colour continues to be of the highest importance to further uncover the evolution of skin colour, race and ethnicity. It is also extremely beneficial from a medical standpoint to understand various health and skin conditions and diseases.
*Melanin (our skin's pigment) is produced by melanocytes which are found in the deepest layer of our skin (the Epidermis). Skintypes with abundant melanocytes will have darker skin tones, these individuals are also prone to have differing skin problems to those with a lower concentration of melanocytes.
*Hyperpigmentation (melasma), or extra pigment, affects certain regions of the face. It can occur after injury to the skin or even post-pregnancy (often known as ‘pregnancy mask’). Some people with skintypes abundant in melanin are also more prone to problems with excess oiliness and/or acne.
Let us hope that our long history of classifying people based solely on skin colour is nearing a permanent end, and that we will finally accept that we are members of the same, human family. The real differences in skin colour have too often gone unrecognised – as they are merely dermatological; and not a social, religious, cultural, societal phenomenal difference. It is time to celebrate all shades of nude and love every spectrum of skin. With education, awareness, and thoughtfulness, perspectives will be altered and we will finally evolve into a fully accepting and embracing species.
WHAT YOUR SKIN REQUIRES EVERY DAY - THE BASICS
Each day, you should be sure to provide your skin with the following...
HYDRATION
Drinking plenty of water.
CLEANSING
Thorough cleansing, twice a day. At night, make sure you remove all your make-up and cleanse properly before going to bed.
NUTRITION
Balanced nutrition.
MOISTURISING
This is a necessary step even for those who have oily skin.
SUN PROTECTION
Sun protection, sun protection, sun protection. It is absolutely crucial to protect your skin from harmful UVA and UVB light rays. Sunscreen (SPF 30 or higher) is recommended every day. This will help prevent sun damage, skin cancers, premature ageing, fine lines and wrinkles.
Understanding Your Skin Cycle - The Regenerative Process
Just as we see in nature, our skin has a unique cycle of renewal and regeneration. The outermost layer - the epidermis - is constantly regenerating every 28 - 35 days. This regeneration is dependent on several factors: age, health, lifestyle, and of course genetics. Just as we are more impacted by injury, with less resilience and miss the ‘bounce back’ we had as children or adolescents; the healing process, (as well as overall skin regeneration) slows as we age. This is why a healthy lifestyle, adequate vitamins and minerals, sleep, and protection from harmful environmental factors are all so important.
When we understand our skin, we become more patient and realistic about the things we must do to maximise our skin health. This means taking the time every day on a skin regime that works for you. Always be sure to gently cleanse, moisturise and hydrate and when it comes to resolving skin problems or concerns, be patient. Clear and healthy skin is achievable and you will get there!
Skin & the Ageing Process
What Are the Skin’s Proteins?
Collagen
Collagen is the most plentiful protein in the skin, making up 75-80% of your skin. Collagen and elastin are responsible for warding off wrinkles and fine lines. Over time, the environment and ageing reduce your body’s ability to produce collagen.
Elastin
Think elastic. Elastin is found with collagen in the dermis. It’s another protein, responsible for giving structure to your skin and organs. As with collagen, elastin is affected by time and the elements. Lower levels of this protein cause your skin to wrinkle and sag.
Keratin
Keratin is the main protein in your skin, and makes up hair, nails, and the surface layer of the skin. Keratin is what forms the rigidity of your skin and helps with the barrier protection that your skin offers.
Intrinsic and Extrinsic Factors
As the skin ages, there is a reduction in both the number and size of skin cells which causes it to function less effectively as a protective barrier and temperature regulator. The structure of skin becomes increasingly thin over time due to intrinsic ageing effects causing depletion of collagen, elastin and hyaluronic acid. These changes result in the skin becoming increasingly dry and also an increase in fine lines, wrinkles and even deep furrows. Aesthetics aside, ageing also affects the skin’s immune response, increasing the risk of certain skin cancers. So what can be done? Ageing is a natural and inevitable thing; it cannot be prevented. The most important thing is to take care of your skin with a good skincare routine, healthy diet and lifestyle (limited drinking and no smoking) and of course, to protect ourselves from harmful UV sun radiation. Don’t fixate too much on turning back the clock; focus on protecting your skin, to allow it to glow (with the help of good serums), and maintain hydration and moisture so that your skin has a nice texture. Skin can be beautiful at any age!
UV Light & Ageing
Approx. 50% of UV damage is caused by the formation of free radicals which are harmful to skin cells. UV light has been shown to activate enzymes known as matrix metalloproteinases; these break down collagen, damaging the skin’s support structure, making it sag or present deeper wrinkles. These enzymes also have the ability to prevent new collagen production. The result - sagging, wrinkles and thin, inelastic skin.
Sugar & Ageing
There is more and more research and evidence supporting the thought that sugar will contribute to premature skin ageing and inflammation by a process known as glycation. As the consequences of glycation accumulate over time, it directly damages collagen and elastin, which give our skin its structure, support and tightness. The result-reduced skin elasticity, textural changes, wrinkles, possible skin irritations and acne, and skin sagging.
Smoking & Ageing
Smoking has been associated with premature skin ageing and wrinkling, poor or delayed wound healing, and the worsening of a number of skin diseases. The link between smoking and wrinkles has been known for many, many years. Research shows that women are more susceptible to this than men. Smoking is associated with fine lines around the eyes (crows feet) and mouth (smoker lines). Aside from early drinking, smoking causes a number of recognised facial changes. These include thinning of the skin, facial redness and prominence of the underlying bony contours of the face. Smoking appears to activate enzymes that break down collagen and elastin fibers. The result - reduced skin elasticity, skin sagging, redness, and premature wrinkles.
“When we understand the biology and science of our skin we can make positive and reversible lifestyle changes in order to better achieve the results and overall appearance of our skin.”
