A Crash Course in Skin Structure

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It’s impossible to understand skincare without first understanding a bit about the skin and how it works. In this guide, I’m going to try to distil the basics from what is quite elaborate science to give you everything you need to know. Human skin is a complex biological organ straddling the junction between beauty, health and disease. Rightly or wrongly, good skin, particularly of the face, has long been considered a marker of attractiveness. It is closely linked not just to the visual aesthetic, but also to self-esteem, confidence and how we view ourselves.

Skin, however, is more than just skin-deep. Our skin has a number of important physiological roles in maintaining health: it provides a physical and biochemical barrier to the outside world, simultaneously protecting us from ultraviolet (UV) light from the sun, preventing water loss and blocking the entry of unwanted microbes and chemicals. Cells of the immune system are ubiquitous in the skin, preventing infection. Body temperature is regulated by blood vessels in the skin.

Skin is a vital sensory organ and site of vitamin D production. We can become so obsessed with making our skin look good that we forget to thank it for all the amazing things it does for us every day.


To understand exactly how beauty products work, why common skin problems occur and what happens to our skin as it ages, it is important to have a basic understanding of normal skin structure and its constituent components. The skin has two main parts: the upper epidermis and the lower dermis.

These together sit on top of a layer of fat and connective tissue that gives the skin its support. The outermost layer of the skin – the upper part of the epidermis – is known as the stratum corneum. This is made up of dead skin cells that are integral to the skin’s function as a barrier. Skin cells turn over approximately every twenty-eight days, with cells from the upper layers being continually shed and replaced by cells from deeper layers.

The epidermis

The epidermis is the outermost part of the skin, the bit that gets up close and personal with the outside world. To do its job successfully as the first line of defence, it has four main cell types, each with its own important role to play.


a) Keratinocytes

The main cell in the epidermis, keratinocytes produce the protein keratin, which provides the skin with physical protection and waterproofing. You may already be familiar with keratin as it’s also the main component of hair and nails, and can also be an ingredient in some personal-care products.

b) Melanocytes

These cells produce the pigment melanin, which gives our skin its colour and protects us against UV light from the sun.

c) Langerhans cells

Langerhans cells are part of the immune system and are ready to seek and destroy any microbes that may invade the skin.

d) Merkel cells

These sensory cells are found deep in the epidermis, and provide us with the sensation of touch.

The dermis

The dermis sits below the epidermis. It is often divided into two layers: the upper ‘papillary’ dermis and the lower ‘reticular’ dermis. The papillary dermis is rich in nerve endings whilst the reticular dermis provides the skin with its structural support and elasticity, and is rich in collagen, elastin and hyaluronic acid. The beauty industry and anti-ageing market has taken much interest in these molecules, and as the terms are often thrown about in writing and talk on skincare, they definitely warrant a closer look.


a) Collagen

Collagen is one of the most abundant proteins in the body. It forms a scaffold that gives strength, rigidity and support to the skin. There are at least sixteen different types of collagen in the skin, although 80 to 90 per cent of human collagen is of types 1, 2 and 3. Gram for gram, collagen is stronger than steel. You can rebuild your skin taking supplements.

b) Elastin

Elastin is another connective tissue protein found in skin. As its name suggests, elastin gives skin its elasticity; indeed, its properties are often compared to those of elastic bands: it allows skin to resume its original shape after being stretched, pinched or poked. You can try bone broth diet to erase wrinkles and improve skin structure.

c) Hyaluronic acid

Hyaluronic acid belongs to a group of compounds known as glycosaminoglycans, and also forms part of the skin’s framework. It is essentially a very large sugar molecule with a gel-like consistency. Hyaluronic acid has a unique capacity to bind over 1,000 times its own weight in water. Its purpose in skin is to keep it soft, plump and hydrated. Hyaluronic acid is a popular constituent in skincare due to its moisturizing properties; it can also be injected into, or under, the skin in the form of dermal fillers.


The process of getting older outwardly can be seen in the skin before any other organ of the body. Changes are visible to us and to those around us and growing old cannot be hidden, unlike many other medical issues. We are living longer than ever before and, for some people, the natural changes associated with skin ageing can be seen as undesirable or even unhealthy. The anti-ageing market continues to grow in lockstep with this, often in response to (but also frequently driving) exactly these kinds of concerns.

The science behind skin ageing

As skin ages, there is a reduction in both the number and size of skin cells. It functions less effectively as a protective barrier, temperature regulation is less efficient and there is a decline in the production of sweat, sebum (oil) and vitamin D. The skin itself becomes increasingly thin over time due to a steady reduction in collagen, elastin and hyaluronic acid (it is commonly quoted that collagen production in the skin falls by 1 per cent each year after the age of twenty).

Cells turn over less quickly and wound healing is relatively impaired. To the external observer, these changes become apparent as dry skin, fine lines, deep furrows and wrinkles.

Skin starts to sag as it loses its support and textural changes appear. Broken blood vessels, thread veins and uneven skin pigmentation become more prominent. Frighteningly, some of these changes can set in as early as your late twenties or early thirties. Aesthetics aside, ageing also affects the skin’s immune response and certain skin cancers become more common as we get older.


Skin ageing occurs for a variety of reasons; some of these are under our control (extrinsic factors) whilst others are not (intrinsic factors). We call them intrinsic and extrinsic ageing. Let’s look at these in more detail.

Intrinsic ageing

Intrinsic, or ‘chronological’, skin ageing is inevitable and, with our current understanding, cannot be prevented in practice; it happens to all of us and is largely genetically determined. If your parents aged well, the chances are good that you will also. We have learned much about the mechanisms of ageing in recent years and a number of underlying causes have been hypothesized. These include:

a) Telomere shortening

Our DNA is tightly packaged into thread-like structures called chromosomes. Telomeres are specialized regions found at the ends of chromosomes and are analogous to the plastic tips found at the ends of shoelaces. Telomeres prevent the ends of the chromosomes fraying or sticking to one another. Each time a cell divides, its telomeres get shorter, and when they get too short, the cell is no longer able to divide; it consequently becomes inactive or dies.

This process of telomere shortening has been linked to skin ageing as well as certain human diseases. Although there is a lot of ongoing research in this area, we don’t yet understand telomeres well enough to develop a safe cure for telomere shortening.

b) Mitochondrial damage

Mitochondria are the tiny ‘powerhouses’ inside human cells, converting oxygen and nutrients into the chemical energy that powers them. Energy production generates free radicals, harmful molecules which have the ability to damage the cell itself over time and if allowed to accumulate. The processes by which mitochondria generate energy, therefore, also have the ability to damage it, rendering cells past their ‘sell-by’ date.

c) Hormonal changes

Hormonal changes, particularly in women, are also thought to contribute to intrinsic skin ageing. Women are more vulnerable to hormonally induced ageing than men due to the more complex hormonal patterns that occur not just over the course of their monthly cycles, but also during their lifetime as a whole. After the menopause, levels of the hormone oestrogen decline. This has been linked to a loss of skin elasticity, reduced hydration and reduced water-binding capacity. Skin changes are noticeably significant after the menopause.

Extrinsic ageing

Now, extrinsic factors are the ones we have the ability to control or change. Extrinsic ageing occurs against the background of intrinsic ageing. And whilst I love basking in the summer heat, UVA and UVB rays in sunlight are the biggest culprits implicated in the skin’s extrinsic ageing process. Sunlight also contains other wavelengths of light, including infrared-A and high-energy visible light, and recent data suggests that these may also have a lesser role to play. So, if you want to keep your youthful good looks, sun protection is an absolute must.

To put all this into perspective, the effects of sunlight are thought to contribute a whopping 80 to 90 per cent of the visible signs associated with ageing. These include wrinkles, pigmentation, sunspots and reduced skin elasticity. Compare the skin on your buttocks or upper inner forearms to the skin on your face or hands. The latter are subject to chronic sun exposure and are much more likely than the former two sites to show, with age, features such as wrinkles or pigmentation. Scientific research on sets of identical twins confirms that the twin with more sun exposure shows features of skin ageing much earlier.

As they are genetically identical, we can be confident that the difference was due to the environmental factor: the sun exposure. So let’s look at ultraviolet light in a bit more detail, seeing as it’s the cause of many of our ageing woes. UVA is the predominant ray and the ratio of UVA to UVB rays is on average 20:1.

This may come as a surprise, but UVA has the ability to penetrate clouds and window glass, causing damage to the skin. This is something to think about if you spend a lot of time driving or near windows. The proportion of UVA reaching the earth’s surface is relatively constant throughout the year, but due to environmental factors such as cloud cover, the proportion of UVB reaching the earth’s surface peaks in the summer months. In the UK, due to our latitude, there is very little UVB in the winter months.

The different types of UV light interact with our skin at different depths. UVB rays, with a shorter wavelength than UVA, mostly penetrate the upper skin layers or epidermis; it is UVB that primarily causes skin reddening and sunburn. UVA rays have the ability to penetrate the skin more deeply, affecting the lower dermal layers, but do not significantly contribute to redness and sunburn. UVA has long been considered both the ageing and tanning ray. An easy way to remember this is UV A for ageing; UV B for burning . Both ultimately damage your skin, and so not too surprisingly we need protection against both.


UV light causes damage to the skin via a number of molecular mechanisms. We still have a lot to learn in this field but research is providing more answers and therefore driving our skincare choices. About 50 per cent of UV damage is from its causing the formation of free radicals, which are harmful to skin cells. The rest of the damage is from UV light causing direct cell injury and DNA damage. UV light has been shown to activate enzymes known as matrix metalloproteinases; these break down collagen and damage the skin’s support structure, making it sag or deepening wrinkles.

These enzymes also have the ability to prevent new collagen production. What you will see in the mirror as a result of these processes is sagging, wrinkles and thin, inelastic skin – the kinds of things we typically associate with ageing. Research also suggests that UV light causes accumulation of a protein known as progerin. This can limit the lifespan of skin cells and their ability to regenerate; the skin is therefore less effective in protecting us. None of this spells good news for our skin.

However, it is within our control to limit the amount of UV light to which our skin is exposed. Preventing damage is often more cost-effective than treatments trying to reverse the visible signs of ageing. If we think about it in these terms, why spend thousands of pounds undergoing invasive procedures to correct skin damage when you could spend under £20 on sunscreen to prevent the damage in the first place? In this day and age, focus should always be on preventative healthcare where possible. There are factors other than sunshine that also contribute to external ageing to a lesser degree. These include smoking, diet and pollution. Collectively, these non-genetic, environmental factors are sometimes referred to as the ‘exposome’.


There are some important differences in skin of colour or ethnic skin. The pigment melanin, which gives our skin its colour, is present in higher quantities in those with dark skin. Melanin absorbs UV light and has the ability to block free radical damage. Darker skin is therefore relatively more protected from sun damage and ageing. Research suggests that black skin has a natural sun protection factor (SPF) of 13.4 compared to white skin, which is about 3.4.

Skin of colour develops problems with pigmentation more readily than white skin types. Inflammatory skin conditions such as acne, eczema and psoriasis can often leave dark staining in the skin that can persist for months. This is known as post-inflammatory hyperpigmentation. The onset of wrinkles, skin laxity and sagging is less common in dark skin when compared to an age-equivalent individual with white skin. Despite this, even dark skin types are vulnerable to sun damage, just not to the same degree. Prolonged, cumulative sun exposure, however, will still lead to the signs we associate with ageing skin so those with dark skin types should also be practising preventative measures.

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