Skin. We’re covered in it! The largest organ of our body and without it we cease to be. Acting as a barrier between our body and the environment, it protects our muscles, bones, ligaments, nerves, organs and everything else squidgy in there. It also connects us to the world around us.
Skin can tell us a lot about someone and the condition of our skin can be a daily obsession or problem for many. Skincare is big, big business. Here’s a look at skin structure, the layers of the skin, functions and a bit about pigmentation.
What Does Our Skin Tell Us?
Skin varies from person to person and varies in appearance with age, sex and race. It can also change from season to season, and reflects our general well-being, health and lifestyle.
Our skin type and colour is primarily determined by genetics, but out lifestyle choices and things like our health all play a part in how our skin can appear. Medication, hormones, smoking, prolonged sun exposure, working outdoors, illness – they can all affect our skin’s appearance and condition.
What Does Our Skin Do?
The skin’s main functions are:
- Protection: Skin protects our internal bits 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 an acid film, the acid mantle, which discourages the growth of bacteria and fungi.
- Sensation: By stimulating a variety of nerve endings, 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). As the outside temperature increases, our blood vessels dilate to increase heatloss, along with the production of sweat which evaporates to aid cooling. As the temperature drops, our blood vessels constrict, reducing blood flow and heatloss.
- Preventing loss: Skin provides a semi-impermeable barrier to fluid loss and 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: With a low permeability, most foreign substances are unable to get through our skin. Some ingredients can be absorbed by the outer layers of the skin and medicine can be administered through the skin by ointments or by means of an adhesive trans-dermal patch (e.g. nicotine patch).
- Appearance: The health of our skin, lifestyle and age group can generally be seen in our skin. Skin can be enhanced with makeup, decorated with tattoos and piercings and, for a myriad of reasons, can develop a variety of issues or problems, often causing misery for the owner.
Layers of the Skin
Our skin is a complex system of layers, cells, nerves and glands. There are three main layers: the epidermis (the bit on top that we see), the dermis (thick elastic layer underneath) and finally the hypodermis (the subcutaneous or fatty layer).
The epidermis is thinnest, outermost layer of the skin and varies in thickness in different parts of our body (between 0.04 and 1.5 millimeters thick). It is made up of overlapping layers of skin cells and contains no blood vessels, but lots of nerve endings. Even though it is thin, the epidermis has five sub-layers or strata:
- Stratum corneum: Also known as the horny layer and 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 (oils) 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), and any disruption to its processes can cause a variety of skin problems. It’s 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, as it helps to prevent friction between the granular and horny layers. Also known as the clear or lucid layer.
- Stratum granulosum: Also known as the granular layer, 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, then move up through the epidermis layers until they end up flattened and dead on the skin’s surface. This 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 bottom three layers of the epidermis are called the germinative zone and this is where the living skin cells are made.
The top two layers of the epidermis are collectively called the keratinisation zone. Here, the skin cells die off and become progressively flatter, finally begin shed from our topmost layer of skin – a process called desquamation. It takes about three weeks for a newly made skin cells to go from the basal layer to reach the horny layer.
The dermis is much thicker than the epidermis and is strong and flexible. It consists of connective tissue, nerves, sebaceous (oil) glands, hair follicles, sweat glands and lymphatic vessels.
It gives the skin structure and protects the body against stress and strain. Think of it as the skin’s scaffolding!
The dermis consists of two layers:
- Papillary layer: Lies directly beneath the epidermis and is rich in blood vessels which feed and nourish the epidermis layer. It is also this layer that creates the pattern of ridges found on our finger tips (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 fibers. These protein fibers give the dermis its strength, elasticity, flexibility and firmness, allowing us to move and stretch. These fibers become weakened with age, lack of moisture, environmental damage like sun damage and exposure to UV light, or frequent changes in weight (which can result in stretch marks appearing).
The Hypodermis or Subcutaneous Layer
This layer provides the connection between the skin and the underlying muscle and bones, as well as supplying the skin with nerves and blood vessels. It also contains about 50% of our body fat, which protects, cushions and insulates the body, as well as providing fuel.
How Big is Our Skin?
Our skin weighs about 8 pounds (3.6 kilograms) on average and covers 22 square feet (2 square meters). Pretty big.
Our Skin Colour and Pigmentation
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:
- 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 blood 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 more red.
- Carotene: an orange-yellow pigment present in the epidermis and fat cells of the hypodermis.
Uneven pigmentation affects most people at some level, from freckles, sun spots and moles to more extreme uneven pigmentation like 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 itself 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.
- 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, which are triggered by exposure to sunlight, creating darker-coloured spots. Freckles can increase and go darker in colour with sun exposure; likewise they can fade.
- 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 whatever level of sunlight exposure occurs, making them different to freckles.
- Liver spots: Also called “sun spots” referring to the darkened spots caused by a history of unprotected sun exposure in older people. This is a type of lentigo.
- Vitiligo: A skin condition that causes loss of pigmentation from sections of the skin, leaving white patches. Can be debilitating for the sufferer.
- Birthmarks: A small or large irregularity that can appear anywhere on the skin. Vascular birthmarks are caused by an overgrowth of blood vessels e.g. Port-wine stains and salmon patches. Pigmented birthmarks are caused by an excess of melanocytes and pigmentation e.g. moles and café au lait spots.
For people affected by their skin pigmentation, camouflage foundations are incredibly useful.
Professional camouflage makeup products include Dermacolor, Supercover Professional Makeup, Dermablend and Veil. They have a greater pigment content than high-street makeup brands, meaning less product is needed, and 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, so when exposed to too much UV we produce more melanin to protect our skin. The more melanin we have, the darker our skins will look.
So, there’s a look at skin. Incidentally, if you took off all of your skin, it would cover a dining table.
Find Out More:
- The basics of skin from National Geographic
- Facial Anatomy and Proportions
- Working hygienically and identifying some common infectious skin conditions