The skin is a fundamental organ for our life. It acts as the body’s first defensive barrier against bacteria and viruses, and healthy skin maintains water balance and helps regulate body temperature. It is very sensitive and recognizes the slightest touch and pain. It is the most visible and extended organ, covers an area of about 1.8 square meters and constitutes about 16% of our body weight, has a variable thickness depending on the areas, sex, and age, and mostly in the back, hands, plant of the feet and nape of the neck.
The skin has different colors that vary about ethnicity and areas of the body, the color depends on three factors: the blood vessels, the type of skin, and the pigments.
The skin is made up of 3 layers with different functions, from the outside to the inside:
Let’s look at them in more depth.
It is the outermost layer of the skin and is continually renewed, it is made up of 5 superimposed cell layers, it does not have its own blood circulation and depends on the underlying dermis. It acts as the first barrier against external agents and damage and controls the aggression of bacteria and dehydration.
The most important cell layer is the stratum corneum, impermeable to water and with a high regenerative capacity, and it is here that dead cells are regularly eliminated.
The skin is the only body tissue to have permanent growth and renews its surface layer every 20-30 days, this also explains the phenomenon of spontaneous healing.
Most importantly, the stratum corneum, together with sweat and sebaceous secretion, forms a hydrolipidic film on the epidermis that acts as a protective emulsion.
Skin annexes are the sweat glands that produce sweat, essential for thermoregulation, and the sebaceous glands that produce sebum, lubricate, and protect the skin from the aggression of microbes.
It is the intermediate layer of the skin, which serves for nourishment and support and therefore is rich in vessels that carry the penetrated substances into the bloodstream.
It is made up of collagen fibers that give compactness and cohesion to the skin, while the elastic fibers resist traction and deformability.
Inside the dermis, we find fibroblasts, which produce collagen and elastin, and protein-sugar molecules, capable of retaining large amounts of water and swelling, forming a gel that turgor the skin, the most important being hyaluronic acid.
They are fibers that intertwine in bundles, forming a network of extraordinary compactness. They have high tensile strength and a remarkable cellular turnover capacity. After thirty years of age, they begin to degrade and the skin begins to yield and age.
Unlike collagen, it has remarkable elastic properties and its fibers branch out forming a lattice. By intertwining with the collagen fibers, they give elasticity to the entire structure and give the connective tissue strength, support, elasticity, and resistance.
It is the substance in the form of a gel that is found throughout the dermis and vital processes take place in it, such as allowing the passage of oxygen and nutrients, or conversely, carbon dioxide and metabolic waste.
Hyaluronic acid is one of the major constituents, which has the ability to bind large quantities of water, and the elasticity, tone, softness, and firmness of the skin largely depend on the amount of hyaluronic acid present in the dermis.
It is the deepest skin layer and through its spongy structure, it cushions and supports external trauma and also isolates the skin from the underlying organs. It is rich in hypo-soluble substances such as lipids, vitamin A, etc.)
It has various functions:
Energy reserve for drawing in emergency conditions
Through a continuous production of heat due to the fatty acids present, it isolates the underlying tissues from the cold.
Protects and cushions underlying tissues and organs.
Furthermore, the conformation of the adipose tissue is of fundamental importance for the aesthetic aspect.
GLANDS, PILIFERAL FORMATIONS, AND NAILS
The sweat glands are divided into eccrine glands and apocrine glands.
The former produce eccrine sweat which is essential for thermoregulation, as evaporating helps to maintain a constant body temperature. It is composed of water, mineral salts, acids, traces of fats, and carbohydrates. It is clear and has an acid reaction. Sweating is also stimulated by situations of fear or anxiety especially in the palms of the hands and the soles of the feet.
The apocrine glands, on the other hand, are important for carrying the pheromones, they are present to a greater extent in the armpit area and in general where there are hairs, their sweat has acid Ph and if it were not diluted by eccrine sweat it would tend to dry out like glue. The bacteria present on the skin attack and decompose it, forming the characteristic bad smell.
They produce sebum and are found throughout the dermis apart from the palms of the hands and the soles of the feet, and mostly on the forehead, cheeks, chin, chest, and back. The sebaceous gland is constantly renewed and the sebum, rich in fatty substances, mixes with the sweat secretion forming a film that keeps the skin soft and well-hydrated, furthermore its acidity helps to keep aggressive agents such as bacteria and fungi away.
FUNCTIONS OF THE SKIN
The skin is the only organ with an internal and an external front. Internally the function is like the other organs: metabolic exchanges, circulation, and metabolism. Externally, it has functions of defense, separation, protection but also of communication between the person and the outside world.
Functions that need characteristics, such as permeability but also waterproofness, resistance, elasticity, and compactness. But in all this, he must also maintain a great sensitivity that allows us to receive the most subtle stimuli from the outside.
The protection acts against external agents such as viruses, bacteria, and fungi but also against physical, mechanical, and chemical agents.
For example, an acidic substance, if placed on the skin, is neutralized both by the hydrolipidic film and by the stratum corneum, the outermost layer of our skin.
But also the defense against solar radiation is an important feature thanks to melanin, which attenuates the harmful effect.
The skin also regulates and controls the water content of our body, functioning as a semi-waterproof barrier through:
a membrane where the nourishing liquids that come from the underlying dermis pass
Intercellular lipids and natural moisturizing substances – NMF Natural Moisturizing Factor, which help retain water
The surface acidic hydrolipidic film, with a PH between 4 and 6.5
ABSORPTION AND BIOAVAILABILITY
By skin absorption, we mean the passage of a substance through the various layers of the skin until it reaches the capillaries.
An effect this which however does not fall within the cosmetic functions, cosmetics should not reach the bloodstream.
The penetration into the skin and therefore the effectiveness of a cosmetic product depends on various factors:
- Size of the molecule
- State of skin hydration
- The thickness of the stratum corneum
- The residence time of the molecules on the skin
- Molecule delivery
- Age of the person
- Amount of product applied
Bioavailability indicates the amount of cosmetic product that is absorbed through the skin and which can therefore carry out its activities.
The penetration of substances and their presence in the deeper layers of the skin is essential to make the results effective, especially concerning skin aging, thus acting on the cause of the problem and not on the external effect.
In fact, we must say that the skin naturally constitutes a chemical and physical barrier and opposes the passage of these substances, so the more the product is good, the more it is available to perform its function.
It is also important to know that penetration is influenced by the hydration state of the epidermis, the more this layer is hydrated, the more easily the molecules can penetrate the deeper layers.
Once the various molecules have reached their destination, they perform their specific function by improving the bioavailability of the active substances and consequently the positive aspects.
The skin is also considered an organ of sense, as it allows us to relate to the outside.
It has two types of terminations:
Free, which collect the sensations of pain, are located in the dermis and reach the epidermis
Corpuscular, consisting of the termination of the nerve fiber
The skin reacts to the following stimuli:
To maintain a constant temperature, metabolic heat that exceeds the normal threshold must be dispersed. At this point, the skin comes into action, which regulates the body’s temperature also towards the external temperature, and through the vegetative nervous system makes more blood flow by dilating the blood vessels, at the same time it also acts on the sweat glands by increasing sweating, all this determines heat loss.
On the contrary, when it is cold you sweat much less and the contraction of blood vessels restricts blood circulation in the skin, favoring less heat loss.
DEPOSIT AND ACCUMULATION FUNCTIONS
The skin also acts as a deposit of blood which it directs to other organs as needed. The adipose tissue present in the hypodermis also has a fundamental function that guarantees energy nourishment and its protection.