Skin – we are covered in it! Without the largest organ of our body, we would cease to be. It acts as a barrier between us and the environment, protecting our muscles, bones, nerves, and organs. It also connects us to the world with touch. Skin can tell us a lot about someone and its condition can be a daily obsession or problem for many. Here’s a look at skin structure, the layers of the skin, its functions, and pigmentation.
What Does Our Skin Tell Us?
Our skin type and colour are primarily determined by genetics.
However, environmental and lifestyle choices can affect our skin’s appearance and condition. This includes, for example, getting older, medication, hormones, smoking, prolonged sun exposure, working outdoors, and illness.
Our skin can also change from season to season and reflects our general well-being and lifestyle.
What Does Our Skin Do?
Our skin does a lot for us and its main functions are:
- Protection – skin protects our internal bits and pieces from injury, chemicals and pathogenic invasion. It also helps protect against UVA and UVB sun damage. Sweat and sebum combine on the skin’s surface to create the acid mantle – an acid film that discourages the growth of bacteria and fungi.
- Sensation – happens when a variety of nerve endings are stimulated. Our skin helps us to sense the world around us by responding to touch, heat, cold, vibration, and pressure.
- Temperature regulation – skin controls our internal temperature, keeping a healthy person at about 37 degrees Celcius (98.6 Fahrenheit). If the environmental temperature increases, our blood vessels dilate to increase heat loss. We also produce sweat which then evaporates, helping us to cool down. Conversely, as the temperature drops, our blood vessels constrict, reducing blood flow and heat loss.
- Preventing fluid loss – the skin provides a semi-impermeable barrier to fluid loss. It also prevents other nutrients from leaving the body.
- Storage and synthesis – skin stores lipids and water and synthesises vitamin D via sunlight exposure.
- Excretion – salt, urea and other chemicals are excreted via sweat.
- Absorption – most foreign substances are unable to get through our skin. However, some ingredients can be absorbed by the outer layers of the skin. Similarly, medicine can be administered through the skin by ointments or an adhesive transdermal patch (for example, a nicotine patch).
- Appearance – our health, lifestyle and age group can generally be seen in our skin. We can also decorate our skin with makeup, tattoos and piercings. Our skin can also develop a variety of issues or problems, for many reasons, often causing misery for the owner.
Skin Structure & the Layers of the Skin
Our skin is a complex system of tissue, cells, nerves, and glands. It consists of three main layers:
- Epidermis – the bit on top that we see and where skin cells are made.
- Dermis – thick elastic layer underneath that gives our skin structure and support.
- Hypodermis – the subcutaneous or fatty layer that keeps us warm.
The epidermis is the outermost layer of the skin and is also the thinnest of all the layers. It varies in thickness on different parts of our body from between 0.04 and 1.5 millimeters.
The epidermis is made up of layers of skin cells that overlap each other. It also has lots of nerve endings, but interestingly no blood vessels.
New skin cells are made all the time in the epidermis. It takes about three weeks for newly-made skin cells to reach the outmost layer of our skin, to then be shed away.
Even though it is thin, the epidermis has five sub-layers or strata, divided into two main zones:
1) Keratinisation Zone
The top two layers of the epidermis are collectively called the keratinisation zone. Here, the skin cells die off and become progressively flattened, until they are shed off our skin – a process called desquamation.
- Stratum corneum – also known as the horny layer, it is composed of several layers of flat, scale-like cells that are continually being shed and replaced. The skin cells in this layer are dead and they combine with lipids produced by the skin to produce a protective, water-resistant layer. This layer is important for maintaining the integrity and hydration of the skin (the oil traps the water in the skin cells). Any disruption to its processes can cause a variety of skin problems. It is this layer that we scrub and polish to exfoliate loose dead cells to refresh our complexion.
- Stratum lucidum – a thin, clear layer of dead skin cells found in areas of thicker and non-hairy areas of skin, like our hands and feet. It helps to prevent friction between the granular and horny layers. Also known as the clear or lucid layer.
2) Germinative Zone
The bottom three layers of the epidermis are collectively called the germinative zone. This is where the living skin cells are made.
- Stratum granulosum – also known as the granular layer. It is where keratin proteins and water-proofing lipids are produced and organised.
- Stratum spinosum – is where cells start to synthesis keratin.
- Stratum germinativum – also known as basal layer. This final layer of the epidermis is responsible for continually renewing the epidermal cells. All skin cells start life right here through a process of cell division called mitosis. The skin cells then move up through the epidermis layers until they end up flattened and dead on the skin’s surface. The basal layer also contains melanocyte cells, which produce the brown pigment called melanin that provides the skin’s natural colour and helps to protect against sun damage.
The dermis is much thicker than the epidermis and is strong and flexible. It gives the skin structure and protects the body against stress and strain. In a word, it is the skin’s scaffolding!
It consists of connective tissue, blood vessels, nerves, sebaceous glands (the oil glands), hair follicles, sweat glands, and lymphatic vessels.
The dermis consists of two layers:
- The papillary layer – lies directly beneath the epidermis and is rich in blood vessels that feed and nourish the epidermis layer. It is also this layer that creates the pattern of ridges found on our fingertips (yup, our fingerprints!), palms, soles, and toes, helping us to grasp by increasing friction.
- Reticular region – composed of dense, irregular connective tissue with collagen and elastin fibres. These protein fibres give the dermis its strength, elasticity, flexibility, and firmness, which allows us to move and stretch. However, these fibres become weakened with age, lack of moisture, environmental damage like sun damage and exposure to UV light, or frequent weight changes (which can result in stretch marks appearing).
The Hypodermis or Subcutaneous Layer
This layer is not technically part of the skin itself but is an essential player nonetheless.
It provides the connection between the skin and the underlying muscle and bones. It also supplies the skin with nerves and blood vessels. About 50% of our body fat is contained in this layer – and this fat protects, cushions, insulates, and stores energy.
Skin Colour Pigments
Human skin shows a wide range of diversity and colours and is determined primarily by our genes.
Skin colour is determined by at least five pigments, the most important of which is melanin:
- Melanin – a brown-black pigment made by melanocyte cells in the epidermis. The amount of melanin in our skin is primarily determined by genetics and creates our natural skin colour. Black skins have a greater concentration of melanin than white skins, and albinism occurs when there is little or no melanin produced by a person.
- Haemoglobin – a purple-blue pigment, found in red blood cells in the blood vessels in our skin.
- Oxyhaemoglobin – a red pigment found in the blood vessels that are present in our skin. When we blush or are hot from exercise, it is the blood vessels dilating that causes us to look redder.
- Carotene – an orange-yellow pigment present in the epidermis and fat cells of the hypodermis.
- Melanoid – a derivative of melanin.
Uneven pigmentation affects most people at some level. Freckles, sunspots and moles are all created by concentrations of pigmentation. More extreme examples include vitiligo and port-wine stains.
Pigmentation can be affected by several factors including UV exposure, medication, hormones, heredity, medical conditions, the thickness of the skin, and healed injuries.
Some common terms and conditions relating to skin pigmentation are:
- Hyper-pigmentation – means darker than normal pigmentation, which appears as darker patches of skin.
- Hypo-pigmentation – means the absence of pigment resulting in lighter or white patches, as seen in conditions like vitiligo.
- Freckles – small patches of skin with more of the brown pigment melanin. Freckles are triggered by exposure to sunlight, creating darker-coloured spots. They can increase and go darker with sun exposure.
- Lentigo – is an area of darker pigmentation that has an increased number of melanocytes (which produce melanin). A lentigo (plural: lentigines) is stable in its colour no matter what level of sunlight exposure occurs. This makes them different from freckles.
- Liver spots – also called sunspots. These are the darkened spots on older people, caused by a history of unprotected sun exposure. Sunspots are a type of lentigo.
- Vitiligo – a skin condition that causes loss of pigmentation from sections of the skin, leaving white patches.
- Birthmarks – a small or large irregularity that can appear anywhere on the skin. Vascular birthmarks are caused by an overgrowth of blood vessels – for example, Port-wine stains and salmon patches. Pigmented birthmarks are caused by an excess of melanocytes and pigmentation – examples include moles and café au lait spots.
Camouflage Makeup Products
For people who feel affected by their skin pigmentation, especially when larger areas of skin are involved, camouflage makeup foundations are incredibly useful.
Professional camouflage makeup products include Dermacolor, Supercover Professional Makeup, Dermablend, and Veil.
Camouflage products have a greater pigment content than regular high-street makeup products, meaning less product is needed to provide good coverage.
They come with powders that really set and waterproof the foundations. This means they will stay put in water and all weather conditions.
We need some sunlight to produce vitamin D, but excessive ultraviolet (UV) light can harm the skin. Melanin controls how much of the sun’s ultraviolet radiation (UVA and UVB) penetrates our skin.
While a little direct sunlight is good for us, too much UV radiation is very damaging to our skin. When exposed to too much UV, we produce more melanin to protect our skin. The more melanin we have, the darker our skin will look.
And this is tanning – it is simply a mechanism for our skin to protect us against sun damage.