GLOSSARY

* Acne : Acne is an inflammatory dermatosis of the pilosebaceous follicle. It most often appears in adolescence but it can also appear in adults, it is then called "late acne". Clinically, the first signs are hyperseborrhea accompanied by comedones which then evolve into papules or pustules characterized by “acne pimples”. This is one of the first skin problems encountered in black, dark and mixed skin. Keloid acne of the neck: Keloid acne is an inflammatory dermatosis of the pilosebaceous follicle. It is a sub-specificity of acne. It creates pustules, nodules but their scars form a keloid scar. These lesions most often appear on the scalp or the back of the neck. It is a dermatosis frequently encountered in black, matt and mixed skin.

* Adipocyte : Adipocytes or adipose cells have the specific role of storing fat not used by our body. In the skin, they are located in the hypodermis and constitute the adipose tissue. There are types, brown which helps maintain constant body heat and white which serves as an energy reserve for the body.

*Aïnhum : Aïnhum disease or Dactylosis spontana is a skin condition that mainly affects black, dark and mixed skin. Located on the toes and more particularly on the last, it is characterized by a painful constriction which over the long term can lead to amputation of the latter. There are two types: the “true” Ainhum, whose origin is poorly known. The others are pseudo-ainhum which have either an origin of inflammatory restriction or infiltration of a foreign body.

* Albinos : Albinism is an inherited and rare genetic disease that is characterized by hypopigmentation of the white skin, hair, hair and pigmented structures of the eye. This lack of melanin pigment gives albinos a white complexion and hair. It is a global disease and affects everyone regardless of gender or ethnicity. There is no treatment but it requires special monitoring because the skin is more sensitive.

* Alopecia : Alopecia is the abnormal loss of hair and / or hair related to poor renewal which is caused by a depletion of keratin. Several causes are possible: genetics, stress, hormones, mechanical tensions (braids or bun too tight), or even the use of chemical care (bleaching, straightening)

* Arteriole : An arteriole or precapillary artery is a blood vessel 40 to 110 µm in diameter which connects to the start of an artery and leads to capillaries. The arteriole carries nutrients from the heart to the skin cells.

* LANGERHANS cells : Langerhans cells are star-shaped epidermal cells. They are responsible for the immune defense of our skin. Indeed, they have the ability to alert the immune cells if an external pathogen penetrates the skin, to activate the lymphocytes by presenting them directly with the antigen of the latter or even sometimes to eliminate it directly by phagocytosis.

* Merkel cells : Merkel cells are the epidermal cells responsible for perception and sensations to touch. It plays the role of mechanoreceptor thanks to their many nerve endings and this is what allows us to detect, locate and appreciate the shape or texture of an object in contact with our skin. They are irregularly distributed and are more abundant in the lips, palms, fingers and feet, which explains this greater sensitivity in these areas.

* Keloids : Keloid scars are so-called fibroproliferative scars which are characterized by an intradermal mass, firm on palpation that can become itchy and/or hypersensitive. It is a healing anomaly that is caused by an abnormal proliferation of connective tissue linked to an overproduction of collagen by fibroblasts. It can appear after a burn, wound, bite or scar but generally three to six months after the trauma.

* Collagen : Collagen is a protein made by fibroblasts in the dermis. Composed of three protein chains, they bind together to form a triple helix and thus become a collagen fiber. They then combine to form a veritable dermal collagen network. It is essential to the skin because it gives it its tone and firmness. This is why when you pinch the skin it returns to its original state. Its production naturally decreases with age, a sign of skin aging.

* Comedogenic : The term comedogenic refers to a cosmetic treatment that can cause comedones. It will tend to clog pores and promote the appearance of blackheads or acne pimples if the person using this treatment has combination to oily skin. Silicones, mineral oils or certain sunscreens, for example, are considered comedogenic.

* Comedones : Comedones are skin imperfections. There are two types, better known as the "whitehead" (closed comedone) and "blackhead" (open comedone). They are due to an overproduction of clogged sebum in the skin pores due to an accumulation of dead cells or impurities on the surface of it.

* Corneocyte : Corneocytes, horny cells, or even dead cells are keratinocytes of the stratum corneum, the most superficial cutaneous sub-layer of the skin and in direct contact with the outside world. They result from the maturation and terminal differentiation of keratinocytes. Thus, they are flattened cells and devoid of nuclei.

*Skin corpuscle : A corpuscle is a sensory receptor. There are different types, each one is located more or less deep in the skin and responds to different stimuli: - Krause corpuscle: sensitive to cold - Meissner's corpuscles: sensitive to light and dynamic contacts (in motion) - Pacini's corpuscles: sensitive to stretching movements as well as to strong pressures. - Ruffini's corpuscles: sensitive to pressure and pain.

* Basal layer : The basal layer is the deepest layer of the epidermis and rests on the dermal-epidermal junction. It is made up of melanocytes, Merkel cells and keratinocyte stem cells. These stem cells have the capacity for self-renewal but also to differentiate and develop into keratinocytes. Thus, this cutaneous sub-layer is essential for epidermal regeneration.

* Corneal layer : The horny layer or "stratum corneum" is the most superficial epidermal sub-layer, the one in direct contact with the outside world. Made up of corneocyte cells, it constitutes a mechanical protective barrier for the skin and also participates in maintaining constant skin hydration.

* Granular layer : The granular layer is one of the sub-layers of the epidermis, it is located just below the stratum corneum. Composed of flattened keratinoytes, it is divided between 3 and 5 layers. They contain keratothyaline grains and keratinosomes which give this layer its grainy appearance.

* Spiny layer  : The spiny layer or Malpighian layer is one of the sub-layers of the epidermis, it is located just above the base layer or lamina. The keratinocytes present have small thorn-like projections which gave the name of this layer. It also contains desmosomes.

* Depigmentation: Depigmentation is characterized by the appearance of spots on the skin with a lighter complexion than its natural shade. It can be caused by various factors. Genetics, linked to an anomaly of melanogenesis. Or be voluntary and provoked by the use of depigmenting treatments based on hydroquinone or glucocorticoids, for example. This second case is unfortunately very common and constitutes a major public health problem in Africa.

* Dermatosis : Dermatosis means a condition or disease of the skin. It can have several causes, origins or location, it is a very general term. It thus includes various pathologies or skin problems such as hyperpigmentation spots, acne, eczema or urticaria for example.

* Ashy dermatosis : This is a dermatosis that is common in children, even if it sometimes appears in adults. It is characterized by the appearance of bluish and / or gray spots. These spots appear as macules with erythematous edges and appear on the upper limbs, chest and face.

* Dermatosis papulosa nigra : This is a dermatosis characterized by the appearance of small seborrhoeic keratosis located on the face. It affects more frequently subjects with dark skin.

* Dermis : The dermis is a sub-layer of the skin located between the epidermis and the hypodermis. It is subdivided into two sub-layers: the superficial dermis and the deep dermis. The whole is composed of fibroblasts, collagen and elastic fibers, blood vessels, gyco-amino-glycans and other structural molecules. It has a role of support, thermoregulation, healing and hydration.

* Eczema : Eczema or atopic dermatitis is a chronic inflammatory disease of the skin. It is characterized by skin dryness associated with redness, itching, vesicles and scabs that evolve in flare-ups. It develops preferentially in children but can also appear in adults. There is a genetic predisposition but it can also be associated with other factors such as allergies, rhinitis or asthma attacks. Namely, in black, matte and mixed skin it can cause the appearance of hyperpigmentation spots.

* Elastin : Elastin is a protein secreted by fibroblasts in the dermis. It associates in the form of fibers to form a network. They are partly responsible for the elasticity and extensibility of the skin. This is why after pinching or stretching the skin returns to its original shape. Their synthesis takes place during growth and then decreases with age, a sign of skin aging.

* Epidermis : The epidermis is the most superficial layer of the skin, the one in contact with the outside world. It is composed of 90% keratinocyte cells but also Langerhans, Merkel cells and melanocytes. The skin flora is also found there. It is organized in the form of 4 sub-layers (more superficial to deeper): The horny layer, the granular layer, the Malpighian layer and finally the dermo-epidermal junction where the epidermal ridges and dermal papillae are located in order to link the epidermis to dermis. Indeed, the epidermis has no blood vessels, its cells are nourished by the diffusion of nutrients from the dermis.

* Erythema : An erythema is a dermal lesion manifested by localized or diffuse redness, more or less intense, which disappears after applying pressure to the area. It is caused by vasodilation of superficial skin vessels. It can be caused by erythrosis, a burn, a sunburn, a viral or bacterial infection or an insect bite.

* Exfoliation : Exfoliation is a key step in skin regeneration. It is a physiological process that allows it to eliminate dead cells from the epidermis. Note that black, matte and mixed skin exfoliate 2.5 times more slowly than Caucasian skin. It is possible to exfoliate your skin mechanically using scrubs made up of micrograins or chemically using peels.

* Facial Afro-Caribbean Childhood Erutption : It is a granulomatous perioral dermatitis in black children. It is manifested by the appearance of multiple papules on the face. The papules are lupoid on pressure and contain lymphatic fluid.  Fibroblast: Fibroblasts are dermal cells. They are responsible for the secretion of elastin fibers, collagen, glycosaminoglycans and growth factors. Their presence is therefore essential because they give the skin its elasticity, firmness and hydration. Less productive with age, they lead to the appearance of skin aging.

* Hydrolipidic film : The hydrolipidic film is a superficial layer that covers the entire skin. Made up of sweat, sebum and water, it protects the skin and defends it against bacteria. It is therefore a protective barrier.

* Sunscreen : The sunscreens used in the formulation of sunscreens are intended to limit the penetration of the sun's ultraviolet rays. There are: mineral filters, they act like a mirror and reflect UV rays. Chemical filters that absorb them.  Cutaneous flora: The cutaneous flora or cutaneous microbiota brings together all the bacteria, viruses and fungi living in symbiosis on our skin. Present on the epidermis or in the upper part of the hair follicles, it constitutes one of the protective barriers of the skin. They protect it from external attacks and from surrounding bacteria or other pathogens. They also play a role in skin regeneration.

* Pilosebaceous follicle : The pilosebaceous follicle is the association of the hair (hair follicle) and the sebaceous gland (responsible for the secretion of sebum). This is attached to the hair sheath.

* Folliculitis dissectant of the scalp : It is a chronic and rare dermatosis of the scalp affecting mainly black men. It is characterized by the appearance of painful inflammatory nodules, pustules and abscesses which most often lead to the appearance of cicatricial alopecia. The causes of this dermatitis are not yet known.

* Hair sheath : It is an invagination of the epidermis enclosing the hair. We distinguish the external epithelial sheath, which is an extension of the epidermis and which is formed of epidermal cells which extends to the dermis, and the internal epithelial sheath which develops from the base of the hair to the sebaceous orifice.

* Sebaceous gland : The sebaceous gland is responsible for the secretion of sebum which is activated by hormones. Attached to the hair, together it constitutes the pilosebaceous follicle.

* Sweat Gland : Sweat or sweat glands are specialized glands that secrete sweat. There are two types: Eccrines, which produce sweat composed of 90% odorless and colorless water directly on the surface of the skin. The apocrines are very localized (armpits or genitals). They have a very limited flow and are activated by emotions or stress. Their sweat first flows into the sheath of the hair and then the surface of the skin.

* Hypodermis : The hypodermis is the last layer of the skin, the deepest. It serves as an interface between the dermis and the mobile structures (muscles and tendons). Consisting of a rich vascular network, connective and adipose tissue, it protects the body from shocks and ensures the maintenance of a constant skin temperature.

* Ichthyosis : This is a genetically rare chronic dermatosis. It is characterized by very dry skin with an excessive presence of scales and can be accompanied by redness, skin cracks or painful bubbles. Its name means fish in Greek because the skin would then have a "fish scales" appearance.

* Dermo-epidermal junction : The dermo-epidermal junction separates the dermis and the epidermis. It contains plaques, proteins and anchoring filaments that allow it to ensure dermo-epidermal cohesion and play a role of barrier and filter (flow of nutrients) between these two skin layers.

* Keratin : Keratin is a fibrous protein, rich in sulfur amino acids, insoluble in water and very resistant. It is created by keratinocytes during keratinization. Present in the epidermis, hair, hair and appendages, it is organized in the form of fibers and plays the role of intercellular cement. It therefore participates in part in the protection of the skin against external aggressions by ensuring strong cellular cohesion.

* Keratinocytes : Keratinocytes make up 90% of epidermal cells. They are born at the base of the epidermis thanks to stem cells then they migrate and become specific until they reach the stratum corneum and become corneocytes. They are responsible for the synthesis of keratin, essential lipids, and NMF. Their presence is essential for the proper functioning of the skin, especially since it forms a protective barrier, thus protecting it from external aggressions.

* Keratinosomes : Keratinosomes or Oadland bodies are small oval organelles present in the keratinocytes of the Malpighian layer. They synthesize keratin, an essential element for the skin

* Palmoplantar keratoderma : Palmoplantar keratoderma is a rare hereditary dermatosis characterized by hyperkeratosis (thickening of the skin) localized on the palms of the hands and soles of the feet. Other causes are possible such as an endocrinology disorder or an infection for example.

* Keratosis pilaris : Keratosis pilaris or keratosis follicularis is a genetic dermatitis. Characterized by thicker, rough skin with the presence of small pimples mainly on the arms, thighs and buttocks; it is a real skin problem. Indeed, it is caused by an overproduction of keratin which blocks the hair follicles and there is currently no specific treatment. It appears mainly during childhood and adolescence and disappears definitively or not naturally with age.

* Lentigo : The lentigo or mole is a small brown spot that can sometimes be raised. It is particularly noticeable when present on the face, hands and neck. There are different types: Lentigo senile (old age) or actinic (solar)

* Lichen planus : This is a chronic and recurrent inflammatory dermatosis that preferentially affects adults. It is characterized by itchy purplish scaly skin elevations that are mostly located on the wrists and ankles. The real cause is unknown but we know that it can appear as a side effect to certain treatments such as diabetes or hypertension.

* Actinic Lichen Planus : Actinic lichen planus is a sub-specificity of Lichen Planus. It appears exclusively on photo-exposed areas such as the face, neck and the back of the hands, for example. This dermatosis is more common in hot countries such as India, the Maghreb or East Africa.

*Extracellular matrix : The extracellular matrix corresponds to a set of extracellular macromolecules such as collagen and elastin fibers, structural glycoproteins, etc. It is mainly secreted by fibroblasts.

* Melanin : Melanin is the natural pigment that gives skin, hair and eyes their colors. In the skin, it is synthesized by melanocytes in melanosomes and there are two types: pheomelanin (carcinogenic red and yellow pigment) and eumelanin (black, brown and photoprotective pigment).

* Melanocyten : Melanocytes are the epidermal cells responsible for the synthesis of melanin. Once carried out, they transmit the melanosomes charged with melanin to the keratinocytes thanks to their filaments. Present in the epidermis but also in the hair follicles and the eye, they give everyone their natural colors.

* Melanogenesis : Melanogenesis is the term for the synthesis of melanin. It takes place in the melanocytes and more particularly in its organelles called melanosomes. The synthesis is specified from Dopaquinone thus creating two types of melanin: Pheomelanin and eumelanin. Once done, the melanosomes diffuse to the keratinocytes to give the skin its natural color. A disruption of this causes hypopigmentation (white) or hyperpigmentation (brown) spots

* Melanoma : Melanoma or malignant melanoma is a skin cancer that develops from melanocytes. It comes in the form of pigmented spots that turn into nodules or moles. The factors favoring its appearance are genetics, sun exposure, phototype and the initial presence of moles. It is important to treat it in time to prevent skin cancer cells from reaching distant organs such as the lungs or the liver.

* Transient neonatal pustular melanosis : Neonatal pustular melanosis is a benign dermatosis most often affecting black skin. It is characterized by the appearance of pustular vesicles rapidly evolving into small persistent pigmented macules between a few weeks and months.

* Melasma : Melasma or pregnancy mask is a dermatosis that occurs in particular in pregnant women but also under contraception. It is characterized by hyperpigmentation of the skin on the areas most exposed to the sun such as the cheeks, forehead and nose. This is caused in part by the overproduction of endogenous hormones related to pregnancy or contraception, overexposure to the sun without protection or the adverse effect of a drug.

* Arrector muscle : The arrector muscle of the hair is a smooth muscle of the skin. It is attached to the pilosebaceous follicle (base of the hair) and extends to the epidermis (surface of the skin). It reacts to various stimuli and creates during its contraction the straightening of the hair. It participates in the thermoregulation of the body when the stimulus is cold and it generates shivers.

* NMF (Natural Moisturizing Factor) or Natural Hydration Factor : The Natural Moisturizing Factor is composed of amino acid, lactic acid, urea, sugar, minerals and other various skin elements. Present in the stratum corneum, it maintains hydration in the epidermis. Indeed, thanks to their hygroscopic and water-soluble properties, they have the ability to capture and retain water in the skin.