Scientific Area

Structure and chemical composition of the scalp

CATEGORIES SCIENTIFIC AREA

Scientific collaboration between Professor Marco Toscani and Dr. Pasquale Fino, Chair of Plastic, Reconstructive and Aesthetic Surgery, Umberto I Health Center – “Sapienza” University of Rome.

The scalp is an ultra-specialized area of the skin, where hair is anchored. Like other hair, also the hair on the scalp originates from a hair follicle, called a bulb.

Since it is skin (like all other areas of the body), the scalp is susceptible to problems such as imbalances, anomalies, disorders or actual illnesses. The scalp is responsible for protecting the brain, not just through the presence of hair, but also through thermoregulation of the entire head, filtering the sun’s rays and blocking excessive heat dispersion in cold environments.
The scalp is tightly bound to the galea aponeurotica, the aponeurosis that directly covers the skull, with the interposition of weak connective tissue.

The scalp is composed of: a superficial epidermis, with little pigment and well-protected from light by the hair, and a deeper area, the dermis, in which hair bulbs are densely packed.
Capillaries cross the scalp and bring nourishment to the hair through the blood. Other important functions are carried out by sebaceous glands and sweat glands that, with sebum and sweat, ensure protection and lubrification of both the scalp and hair.
Each bulb corresponds to the outlet of a sebaceous gland. A particular characteristic of the hair derives from the extent of sebaceous gland activity, and related hair problems may depend on this factor too. If the sebaceous glands are very active and secrete a lot of sebum, the hair will appear greasy, covering itself easily in the greasy secretion. If, on the other hand, the activity is reduced and produces a small quantity of sebum, the hair will be dry.
The skin or dermis is composed of two layers, a superficial layer, called the epidermis, and a deeper layer, called the dermis, under which the hypodermis or subcutaneous adipose tissue is located.
The epidermis is separate from the dermis of the basement membrane.

Immagini macro del cuoio capelluto
Immagini micro del cuoio capelluto

The epidermis or epithelial tissue is composed of 4 different types of cells, the most important of which, composed of keratinocytes, is distributed across many overlapping rows of cells divided into 5 layers: the basal layer, the spinous layer, the granular layer, the translucent layer (present only on the palm of the hand and the sole of the foot) and lastly the cornified layer. Keratinocytes are formed and reproduced in the deepest part (the basal layer), and from here, following the aging process, slowly climb towards the surface (in about 28 days), producing within them a protein called keratin, which has a particular resistance to external aggression (soap, oils, solvents, heat and cold, visible and ultraviolet radiation, germs, mold and pathogens, etc…).

The detachment of the now-dead cells from the surface is usually invisible. If, instead, for some reason, due to particular scalp problems, cellular masses form (hundreds or thousands of elements), the detachment becomes visible in the form of flakes (dandruff).
The basal layer is the only one that needs nourishment, which it receives from the underlying dermis. The epidermis is devoid of arterial or venous circulation. The basement membrane is a complex structure with an undulated shape that is responsible for both anchoring the epidermis to the dermis and for allowing and regulating the exchange of substances (nutrients and waste) between the epidermis and the dermis. In the dermis (connective tissue) the cells are scarcer and divided into various types: among these we can note the fibroblasts, mastocytes and macrophages. The most important are fibroblasts, that produce both the “fundamental” gelatinous substance, composed mostly of water, salt, sugar and protein, and various types of fibers (reticular, collagen and elastic), which take on the role of providing support, consistency and elasticity to the tissue itself. The dermis is full of blood vessels, lymphatic vessels, fibers and nerve endings. Finally, the hypodermis (subcutaneous adipose tissue) is composed mainly of interwoven fibrous bands (a direct continuation of those found in the dermis) that outline a series of spaces, called adipocytes, occupied by adipose cells. In the hypodermis there are fewer cells and nerve endings, while blood supply is more abundant. Under the hypodermis are bands of muscular tissue with the correspondent muscles.

Scalp itchiness

Scalp itchiness of varying intensity is a sensation perceived by many people of both sexes.
Itchiness is a scalp problem that leads those afflicted to scratch their skin and is often associated with pain. Many causes of this illness are recognized, which shouldn’t be underestimated as it may cause hair loss or thinning.

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Thin hair

Genetic factors influence and determine the size of the diameter in hair.
Its volume varies from person to person. This is why some individuals are born with thin hair, while others are born with thick hair.

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Hair loss (telogen effluvium)

The term Telogen Effluvium was introduced for the first time by Kligman (*) in 1961 to introduce an acute hair loss of benign origin that follows an intense and short period of stress of different types. Subsequently, Rebora (**) introduced the concept of chronic Telogen Effluvium.

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Life cycle of hair

The life cycle of hair and its subsequent growth occur at a speed of 1-1.5 cm per month. Hair is a living element that follows a follicle cycle with an average duration of 2-6 years. In humans, unlike other mammals that are subject to a periodic change, this cyclic evolution is not synchronous (therefore each hair is independent from the others).

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Grey hair

In the trichological field, with the passing of age hair whitening is seen to follow the greying process of the hair on the scalp (called grey hair). Hair becomes grey (white) following a natural biological aging process of the melanocytes, which are the cells tasked with coloring hair.
In the majority of people, the first grey hairs appear around 35/40 years of age in women and around 30/35 in men.

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Damaged hair

Changes in the hair shaft lead to deterioration with the appearance of ruined or damaged hair.
In healthy hair, the cuticle is whole, with overlapping shingles. Hair with whole ends appears shiny, elastic and brushes easily.

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