UNDERSTANDING YOUR SKIN
It is our external barrier, and its essential function is to protect the body from the environment. It is considered a single organ, because it functions systematically. It is very large, with a surface area of approximately 2 m2 and it weighs 4 kg, accounting for about 16 % of your total body weight. The skin is constantly replenishing itself and changing.
COMPOSITION OF THE SKIN
WHAT IS THE STRUCTURE OF SKIN?
The epidermis
Cell types
The epidermis is divided into layers or strata

Basal layer
Where the keratinocytes are produced.
Spinous layer
The keratinocytes are spindle shaped, and start producing keratin fibres.
Granular layer
The cells produce keratohyalin granules (the precursor of keratin) and these go into the extracellular matrix.
Clear layer or stratum lucidum
Cells have been flattened to confer a greater degree of structure.
Horney layer
This is the outermost layer, which contains many layers of dead cells that offer protection. These cells come loose, through a process called scaling. The sebaceous and sweat glands empty into this layer.
Subcutaneous tissue (hypodermis or subcutis)
The dermis or chorion
The extracellular matrix contains a high proportion of fibres, loosely compacted, collagen (> 75%), reticulin and elastin. It is vascularised tissue that supports and nourishes the epidermis. It accounts for the largest mass of skin and has a maximum thickness of about 5 mm.
This is where the nerve endings responsible for touch and pressure are found, as well as skin appendages:
Piloerector muscle, hair follicle, sebaceous glands, and sweat glands, and blood and lymphatic vessels.
SKIN TYPES
SKIN CONDITIONS
Aging (types of aging)
The epidermis becomes thinner and less efficient at regeneration. The dermis produces less collagen, which causes greater flaccidity. Fat cells are lost from the subcutaneous tissue, decreasing its volume and elasticity.
This happens naturally and the visible effects are the wrinkles and expression lines that gradually appear. The skin loses volume and firmness (lower tissue density).

Blotches

Melanin is the substance that gives skin its colour. Melanin build-up (hyperpigmentation) or lack of melanin (hypopigmentation) causes different types of marks:
Hyperpigmented spots (hyperchromia)
Hypopigmented spots (Hypochromia)
Acne

There are different types of skin lesions (comedones, papules, pustules and nodules).
It is characterised by follicular epidermal hyperproliferation (the cells do not flake off), excess sebum production that blocks the pores, and lesions that cause inflammation and increase in the activity of Propionibacterium acnes.
There are several clinical forms, such as excoriated acne, acne caused by cortisone and acne conblobata.
Excessive Sweating

It affects 2 % of the general population, and there are different therapeutic alternatives, such as topical antiperspirants, botulinum toxin infiltration, iontophoresis, anticholinergics, beta-blockers, antidepressants and even endoscopic sympathectomy.
Rosacea or couperosis

It can cause vascular dilatations (telangiectasisas), papules-pustules (lesions containing pus), flushing, ocular symptoms (itching or blepharitis) or thickening of the surface of the skin that affects the nose (rhinophyma), forehead, cheeks, chin, ears or eyelids.
This treatment is based on skin protection (before exposure to ultraviolet radiation, the cold, etc.), skincare (hypo-allergenic soap) and oral treatments (tetracycline, isotretinoin, sulfones) and topical products (metronidazole, ivermectin, azelaic acid).
In many cases, rosacea can be mistaken for other skin conditions, such as atopic dermatitis or acne, because the symptoms can appear similar to the naked eye.
Bruising

Their frequency depends on capillary fragility.
Their clinical evolution starts with a bright red appearance with inflammation, which turns purple. This happens because the blood starts to coagulate and is then absorbed.
The blood may accumulate within the skin tissue as petechiae (red dots), purple bruises (larger flat areas) or ecchymosis (areas of large haematomas).
This is not to be confused with an erythema, which is a reddening of the skin that becomes paler when pressed.
In many cases, rosacea can be mistaken for other skin conditions, such as atopic dermatitis or acne, because the symptoms can appear similar to the naked eye.
Dehydration

This happens when the layers of skin are unable to hold the necessary ambient moisture or water molecules. Starved of water, the cells die more quickly and the skin flakes because we lose cells that through a hydration structure in deep and surface layers could be maintained.
By adding emollients, this structure is preserved, because water molecules remain in the skin, which can continue to perform its barrier functions. In addition, if we reduce the adverse conditions (ultraviolet radiation, cold, heat, humidity, etc.), we can make skin firm and bright again.
Sensitive Skin

This is usually due to an underlying skin disease such as rosacea, dermatitis (atopic dermatitis or seborrheic dermatitis) or contact eczema.
The strategy for treating sensitive skin is to prevent contact with these irritants, and daily care with hypo-allergenic and non-irritant substances.
SCALP CONDITIONS
Hair
Hair follicle
Each hair grows from a follicle and each follicle has its own cycle, which is independent from those surrounding it. That is why each hair on your head is in a different phase of its life cycle, at any given time. There are between 100,000 and 150,000 hairs on the head of a person without alopecia, of which 85%-90% are in the anagen phase or growth period, 1-2 % in the catagen or resting phase, while 13-14 % are in the telogen or fall phase.
Hair loss
On average, in one day around 70-100 hairs are lost. In normal conditions, these are replaced by new ones generated by the hair follicle.
Eight in ten people who believe that they have alopecia,do notpathological substrate. All that is happening is that we are losing hair randomly and this is not replaced immediately. Therefore, the concept is based on renewal of the hair follicles rather than hair loss. This process, called telogen effluvium, is often seasonal and depends on various factors (the environment or food).
However, there are also genetic factors that affect the speed at which the renewal process occurs, which means that hair falls out at a different speed to the natural renewal process.
Types of hair loss

Diffuse alopecia | Non-scarring alopecia

Alopecia areata | Non-scarring alopecia

Traumatic or drug-induced alopecia | Non-scarring alopecia

Androgenetic alopecia | Scarring alopecia
Hereditary diseases: Ichthyosis, Darier disease, etc.
Infectious diseases: Fungal, bacterial.
Neoplastic diseases: Lymphomas, metastases, etc.
Dermatosis: Lichen planus, systemic lupus erythematosus, sarcoidosis, etc.