The skin is our largest organ and maybe one of the most complicated. Its surface area of two square meters is our first line of defense - it covers us, helps regulate the body temperature and provides protection against the sun, bacteria, and harmful substances. The skin plays an active and important role in the immune system to protect the body from diseases. The human skin is divided into three main layers: the epidermis (the outermost layer), the dermis (the layer directly beneath the epidermis) and the hypodermis (the innermost layer). Each layer is made up of further functional layers which together form an elastic mass of epidermal, dermal and hypodermal cells, immune cells, blood vessels, sebaceous glands, and sweat glands. These cells work together with the trillions of good bacteria and fungi that inhabit the skin and together they determine the skin’s health status. It’s time to rediscover our skin.
THE EPIDERMIS – THE OUTERMOST LAYER
The epidermis is the part of the skin that we can see and touch, the part we typically refer to when we talk about our skin. Generally, it’s only 0.05-0.1 millimeters thick, though slightly thicker on our soles and palms. The epidermis is covered by an emulsion of water and fats known as the hydrolipidic film which is composed of natural humectants such as salts and glycerin together with a unique mixture of cholesterol, ceramides, free fatty acids from sebum, triglycerides and squalene. The hydrolipidic film keeps the skin pliant and acts as a protective barrier against harmful bacteria, fungi and other substances we do not want to penetrate the skin. There is a large number of good bacteria that inhabit the epidermis, which secrete acids (such as lactic acid) to fight off the bad bacteria.
RENEWAL AND PIGMENTATION
Have you ever heard that our skin renews itself every twenty-eight days? There’s a lot of truth in that statement, but the change is gradual: the skin forms new cells and eliminates those that have already done their job. The two main types of cells in the epidermis are keratinocytes and melanocytes. Keratinocytes, which are in the majority, are responsible for regenerating the epidermis. They are embedded in the unique hydrolipidic film that holds the cells of the epidermis together and protects them from dehydration. The skin’s regeneration results from the keratinocytes moving to the outer surface of the skin, the stratum corneum, where they lose their cell nuclei and die. The skin gradually sloughs off the dead cells; several kilos of dead skin is replaced every year.
Melanocytes are pigment cells that produce the color in our skin. They are far less numerous than keratinocytes, with about one melanocyte to every forty keratinocytes. Melanocytes are located in the deepest layer of the epidermis (the basal layer) and have just one function – to secrete pigment. They’re equipped with arms known as dendrites, which channel the pigment they produce into the surrounding keratinocytes to create an even skin tone.
THE SECOND LAYER – THE DERMIS
Below the epidermis lies the next layer – the dermis. In contrast to the thin epidermis, the dermis is up to ten millimeters thick and is at its thickest on our backs. The dermis has a range of specific functions - it maintains skin stability, controls our body temperature, supplies the epidermis with oxygen and nutrients, conducts signals from the touch cells (Merkel cells) to the brain, and plays a significant role in the immune system. This layer is made up of two proteins you may know, collagen and elastin which provide elasticity and are considered to be the key to healthy and youthful-looking skin.
Around the collagen and elastin lies another well-known substance, hyaluronic acid which has a unique ability to bind water and therefore has a filling function. Both collagen and hyaluronic acid are well-known ingredients in anti-aging products since they, in theory, provide resilient and plump skin. However, it’s not possible to just lubricate the face with a cream containing these substances since the molecules are far too large to penetrate the skin.
HYPODERMIS – THE DEEP LAYER
The deepest layer of the skin is called hypodermis and is often referred to as subcutaneous fat. The hypodermis contains a large number of vital blood vessels, nerves, lymph vessels, and it’s also the layer that insulates and protects us against cold. The thickness of this layer varies greatly between different parts of the body and between individuals, some people simply have more subcutaneous fat naturally than others. The hypodermis covering the lower part of the stomach is often up to three centimeters thick, yet there’s hardly any in the face, particularly the eyelids. A lot of research is being done to see whether fat production in the face can be boosted as an antidote to loose, sagging skin.
In contrast, there are other areas where people are keener to reduce the thickness of the hypodermis, namely the part of hypodermis that is home to cellulite. Eighty-five percent of all women have cellulite, which is far more common in women than in men. Estrogen is thought to be a strong contributory factor to this and moreover, men’s thicker skin conceals any cellulite they may have. The structure of hypodermic tissue also differs in men and women. Men’s hypodermic tissue displays a horizontal crosslinked pattern which squeezes fat together, whereas the connective tissue in women’s skin has a honeycomb pattern, making cellulite more visible. It might seem unjust, but the cellulite are there for a good reason – if a woman gets pregnant, her body needs to be able to form a reserve layer of fat and in order to do so, the skin structure women have is needed.