It may cause us a few beauty bothers from time to time, but the skin is an essential part of our bodies. As the largest organ of the human body, it plays host to a whole range of important functions. It’s a protective barrier covering almost every part of the body, keeping away nasty disease-causing bugs. It’s a waterproof layer that separates us from the outside world and keeps us protected against the elements. It allows us to stay at just the perfect temperature in different environments. Not to mention aesthetics…we’d all look pretty strange without our skin!

All these vital roles come about due to the structure of the skin. Like onions and cake, our skin is arranged in layers, each carrying out its own specialised function.

From the top!

The top layer of the skin is the epidermis – the part of the skin we can see on our body. This layer is actually made up mostly of dead skin cells which are removed from the surface in a process called desquamation. These dead cells are renewed by new cells which have migrated up the deeper layers of the skin. As they move up, the cells change in shape and carry out different functions. This migration process is known as keratinisation.

The epidermis is the body’s first line of defence against pathogens and can vary from 0.05 – 1.5mm in thickness depending where it is on the body. This layer of the skin doesn’t contain any blood vessels and relies on the layer below it – the dermis – to supply it with blood.

The epidermis itself is made up of five layers:

  1. Stratum corneum
  1. Stratum licidum
  1. Stratum granulosum
  1. Stratum spinosum
  1. Stratum basale

When keratinisation takes place (the hardening and renewal of skin cells), the cells move up from the stratum basale to the stratum corneum, which is the outermost layer of the skin.

The stratum basale is the bottom layer of the epidermis and acts as a source of new epidermal cells. Within this layer there is a row of stem cells, half of which become a new type of skin cell through differentiation and move up the epidermal layers, and the other half stay in the stratum basale to help replenish the stem cell store (these are the cells which multiply to continually renew our skin cells).

The next layer up is the stratum spinosum. In this layer, the rapidly dividing cells change from being column-shaped to polygon-shaped. This is the layer of the epidermis in which the production of keratin starts, a protein which we’ll discuss in more depth later. The stratum basale and spinosum are known collectively as the malpighian layer.

Then come another few layers, the granulosum and licidum. Molecules such as proteins and lipids are organised in the granulosum, and the licidum acts a buffer between the layers above and beneath it. The stratum lucidum isn’t found in all types of skin but is often present in places where the skin is thicker on the body.

The final layer of the epidermis is the stratum corneum. This outer layer is home to corneocytes which are flattened skin cells filled with keratin. Keratin is a protein which makes up our hair and fingernails, and helps the cells keep their strength and structure and also allows for water absorption into the layer which keeps the skin hydrated. This layer of the skin is tightly controlled, as any tiny change in the equilibrium of this layer alters its conditions and can lead to a number of skin problems

Different skin cell types are present throughout the different layers of the epidermis. We’ve got corneocytes at the top which are removed and replaced, and melanocytes at the bottom which produce melanin. Melanin is the pigment in our skin which helps us get our lovely tans in the summer. But be careful, these cells are also responsible for the skin cancer melanoma. So don’t forget the sun cream!

The dermis

Moving away from the epidermis, the next layer down is the dermis. This layer tends to be much thicker than the layer above it because it contains things like nerves, hair follicles and sweat glands. The dermis is really important in giving structural support to the skin. As we mentioned earlier, the dermis supplies its neighbouring layer – the epidermis – with blood, so it has a great big network of tiny blood vessels called capillaries.

The dermis is a layer of skin where there’s a lot going on. It’s a really active layer, with erector muscles which make the hairs on your arm stand up when you’re cold, and nerve endings which help you sense the things around you as well as a number of different glands which produce lots of useful substances. For example, the sebaceous gland secretes a waxy substance called sebum which provides the skin with lubrication and makes it feel oily. Eccrine and apocrine glands produce sweat, and are found in different places and in different amounts over the body.

There are also pressure sensors in this layer such as meissner’s corpuscle which help us interact with our surroundings. What’s really cool about the dermis is that in certain parts it contains papillae. These are tiny finger-like projections that rise upwards towards the epidermis. This causes ridges to form on the surface of our skin and is what makes up our fingerprints!

Last but not least

The deepest layer of the skin is the subcutaneous layer which contains fat (adipose) cells and blood vessels. These adipose cells, along with some connective tissue, cushion the really big blood vessels and nerves in the skin. The subcutaneous layer is really important in keeping our body temperature at a constant level.

Problems with the skin

Acne

Acne is a skin condition which usually occurs in adolescence. It associated with red, spotty and often itchy skin. Remember those sebaceous glands from earlier? Well these glands get a bit over-excited and produce too much sebum. This isn’t good news as it can block the hair follicles and cause an oily build up on the surface of the skin.

It’s thought that this over-excitement is due to the hormone testosterone. In both men and women testosterone is acted upon by 5-alpha reductase which causes the hormone to send the sebaceous gland into overdrive. So the more testosterone there is, the more active the gland and the more sebum is produced.

In a process called follicular hyperkeratosis, excessive keratin is produced in and around the hair follicles. Combined with excessive sebum production, this means that cells and bacteria clump together on the surface of the skin. This blocks off the oxygen supply to the area which makes the bacteria grow even more.

Xeroderma

Xeroderma (dry skin) occurs when there is an imbalance of lipids and water in the stratum corneum. Like acne, in xeroderma there’s an imbalance in the amount of hormones. But in xeroderma, the sebaceous glands are less active meaning the skin is less lubricated.

Also, the structures between skin cells that usually keep them together are broken up by enzymes causing the skin to become flakey. It’s also thought that ceramide (a type of lipid molecule) causes disruptions in the layers of other normal lipid layers in the skin, weakening them. With lower ceramide levels, the skin cells are more disrupted causing dryer, flakier skin.

There may be a lot more to the skin than you might have thought, with all of its many layers carrying out different functions. So take good care of your skin, because it does a really good job at taking care of you!