Skin – we are covered in it! It is the largest organ of our body and without it we would cease to be. Our skin provides us with lots of benefits. For a start, our skin 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. Additionally, skin can tell us a lot about someone and its condition can be a daily obsession or problem for many. This post covers our skin’s structure, including its layers, functions, and pigmentation.
What Does Our Skin Tell Us?
Our skin type and colour are primarily determined by genetics. However, our skin’s appearance and condition can be affected by environmental factors and lifestyle choices. For example, getting older, medication, hormones, smoking, prolonged sun exposure, working outdoors, and illness can all affect how our skin looks.
Our skin can also change from season to season and, overall, it 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. 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. It also helps protect against UVA and UVB sun damage.
- Sensation – this happens when a variety of nerve endings in our skin 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 Celsius (or 98.6 degrees Fahrenheit). For example, 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, if the temperature drops, our blood vessels constrict. This reduces 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. Vitamin D is synthesised via direct 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. This can be useful for administering medicine through the skin with ointments or adhesive transdermal patches (for example, a nicotine patch).
- Appearance – our health, lifestyle and age group can generally be seen in our skin. Likewise, our skin can develop a variety of issues for many reasons, often causing misery for the owner. We can also decorate our skin with makeup, tattoos and piercings.
Skin Structure - the Layers of the Skin
Our skin structure is made up from 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 – the thick and elastic layer underneath the epidermis. It 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 structure. Furthermore, it is the thinnest of all the skin layers. It varies in thickness on different parts of our body from between 0.04 and 1.5 millimetres.
The epidermis is primarily made up of overlapping skin cells. It also has lots of nerve endings but, interestingly, no blood vessels.
The epidermis is where new skin cells are made. In fact, it takes about three weeks for newly-made skin cells to progress all the way to the top of our skin.
Even though it is thin, the epidermis still has five sub-layers. These are contained in two main zones:
1) Keratinisation Zone
The top two sub-layers of the epidermis are collectively known as the keratinisation zone. Here, the living skin cells die off and become more flattened in shape. They are eventually shed off our skin – a process called desquamation.
The two sub-layers are:
- Stratum corneum – also known as the horny layer. The dead skin cells have a flat, scale-like appearance, which allows them to overlap. The cells are continually being shed and replaced. This layer is important for maintaining the integrity and hydration of the skin. For example, the lipids in the skin bind with the overlapping skin cells to trap water. Additionally, this also provides a protective water-resistant element. Any disruption to these processes can cause a variety of skin problems, including dry or rough skin. It is this sub-layer we scrub and polish to exfoliate loose dead skin cells to refresh our complexion.
- Stratum lucidum – also known as the clear or lucid layer. This thin, clear layer of dead skin cells is found in thicker and non-hairy areas of skin, like our palms and soles. It helps to prevent friction between the granular and horny layers.
2) Germinative Zone
The bottom three sub-layers of the epidermis are collectively called the germinative zone. This is where the living skin cells are made.
The three sub-layers are:
- Stratum granulosum – also known as the granular layer. It produces and organises keratin proteins and water-proofing lipids.
- Stratum spinosum – is where cells start to synthesis keratin.
- Stratum germinativum – also known as basal layer. This sub-layer 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 all the epidermis sub-layers, until they end up flattened and dead on the skin’s surface. The basal layer also contains the melanocyte cells, which produce the brown pigment melanin. This pigment provides the skin’s natural colour and helps to protect against sun damage.
The dermis is much thicker than the epidermis. It is strong and flexible, which gives the skin structure and support. It also protects the body against stress and strain. In other words, it is the skin’s scaffolding!
The dermis layer consists of connective tissue, blood vessels, nerves, sebaceous glands (the oil glands), hair follicles, sweat glands, and lymphatic vessels.
The dermis has two main sub-layers:
- The papillary layer – lies directly beneath the epidermis. It is rich in blood vessels that feed and nourish the epidermis layer. This layer also creates the pattern of ridges found on our fingertips (our fingerprints), palms, soles, and toes. It is thought these ridges help us to grasp items and increases touch sensitivity.
- Reticular region – composed of dense, irregular connective tissue with collagen and elastin fibres. These protein fibres give the dermis strength, elasticity, flexibility, and firmness, which allows us to move and stretch. However, these fibres become weakened with things like age, lack of moisture, environmental damage (like 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 structure itself but is an essential player nonetheless.
The subcutaneous layer provides the connection between the skin and the underlying muscles and bones. It also supplies the skin with nerves and blood vessels.
In addition, about 50% of our body fat is contained in the subcutaneous layer. This fat protects, cushions, insulates, and stores energy for us.
Skin Colour Pigments
Human skin shows a wide range of diversity and colours. This is primarily determined by our genes.
Skin contains 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. Albinism occurs when there is little or no melanin produced by someone’s skin.
- 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 in our skin. When these vessels dilate, they cause us to look red-faced. For example, we look red when we blush or are hot from exercise.
- 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. For example, 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. This can be seen in conditions like vitiligo.
- Freckles – small patches of skin with more of the brown pigment melanin. Freckles are triggered by exposure to sunlight, which encourages darker-coloured spots to form. They can also increase and go darker with further 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, even if it is exposed to further sunlight. This makes them different from freckles.
- Liver spots – also called sunspots. These are the darkened spots seen on older people and are 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
Camouflage makeup foundations can be incredibly useful for people who feel affected by their skin pigmentation. This may be more so when larger areas of skin are involved.
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. This means that only a little of the product is needed to provide good coverage.
The foundations come with powders that help to really set and waterproof it. This means they will stay put in water and all weather conditions.
We need some direct sunlight to produce vitamin D, which is beneficial to us all. Sunlight also makes us feel good.
However, while a little direct sunlight is good for us, too much UV radiation is very damaging to our skin. When we are exposed to too much UV, our skin tries to protect itself by producing more of the dark brown pigment melanin. The more melanin we produce, the darker our skin will look. And this creates a tanned look. In a nutshell, a tan is simply a mechanism for our skin to protect us against sun damage.