Acne: Acne is an inflammatory skin condition affecting the hair follicle. It most commonly occurs during adolescence but can also appear in adults, in which case it is referred to as "late acne." Clinically, the first signs are seborrhea accompanied by comedones, which later develop into papules or pustules, often called "acne pimples." It is one of the most common skin problems encountered in people with black, olive, and mixed skin tones.
Cicatricial acne of the neck: Cicatricial acne is an inflammatory skin condition of the hair follicle. It is a subtype of acne. It creates pustules and nodules, but their healing results in the formation of keloid scars. These lesions most often appear on the scalp or neck. It is a common condition in people with black, olive, and mixed skin tones.
Adipocyte: Adipocytes, or fat cells, have the specific role of storing unused fats in the body. In the skin, they are located in the hypodermis and constitute the adipose tissue. There are two types: brown adipocytes, which help maintain constant body temperature, and white adipocytes, which serve as energy reserves for the body.
Ainhum: Ainhum, or spontaneous dactylosis, is a skin condition that mainly affects black, olive, and mixed skin tones. It is localized on the toes, especially the last one, and is characterized by painful constriction that can, over time, lead to amputation of the affected toe. There are two types: "true" Ainhum, whose origin is poorly understood, and pseudo-Ainhum, which originates from inflammatory restriction or the infiltration of a foreign body.
Albino: Albinism is a rare hereditary genetic disorder characterized by hypopigmentation of the skin, hair, and the pigmented structures of the eye. The absence of melanin pigment gives albinos a white complexion and hair. It is a global condition that affects individuals regardless of their gender or ethnicity. There is no treatment, but special care is needed because the skin is more sensitive.
Arteriole: An arteriole, or pre-capillary artery, is a blood vessel 40 to 110 microns in diameter that connects to an artery and leads to capillaries. The arteriole transports nutrients from the heart to the skin cells.
Langerhans cells: Langerhans cells are star-shaped epidermal cells responsible for the immune defense of our skin. They can alert immune cells if a pathogen enters the skin, activate lymphocytes by directly presenting the antigen, or sometimes eliminate the pathogen through phagocytosis.
Merkel cells: Merkel cells are epidermal cells responsible for the perception and sensation of touch. They act as mechanoreceptors due to their numerous nerve endings, which allow us to detect, locate, and appreciate the shape or texture of an object in contact with our skin. They are irregularly distributed and more abundant in areas like the lips, palms, fingers, and feet, explaining the increased sensitivity in these areas.
Keloids: Keloid scars are fibroproliferative scars characterized by an intradermal mass that is firm to the touch and may become pruritic or hypersensitive. It is an abnormal healing response caused by an overproduction of connective tissue and collagen by fibroblasts. It typically appears three to six months after a burn, injury, insect bite, or other trauma.
Collagen: Collagen is a protein produced by fibroblasts in the dermis. It consists of three protein chains that bond together to form a triple helix and thus create a collagen fiber. These fibers then assemble into a collagen network within the dermis. Collagen is crucial for the skin as it gives it tone and firmness, which is why when you pinch your skin, it returns to its original state. Its production naturally decreases with age, signaling skin aging.
Comedogenic: The term comedogenic refers to a cosmetic product that can cause comedones. It tends to block pores and promote the appearance of blackheads or acne pimples, especially if the person has combination to oily skin. Silicones, mineral oils, and certain sunscreens are considered comedogenic.
Comedones: Comedones are skin imperfections, classified into two types: "whiteheads" (closed comedones) and "blackheads" (open comedones). They are caused by an overproduction of sebum that clogs the pores, due to an accumulation of dead skin cells or impurities.
Corneocyte: Corneocytes, or cornified cells, are dead keratinocytes from the cornified layer, the outermost layer of the skin that is in direct contact with the external environment. They are the result of the maturation and terminal differentiation of keratinocytes, making them flattened cells devoid of nuclei.
Cutaneous corpuscle: A corpuscle is a sensory receptor. Different types exist, each located at varying depths within the skin, responding to different stimuli:
- Krause corpuscle: Sensitive to cold
- Meissner corpuscles: Sensitive to light and dynamic touch (moving)
- Pacini corpuscles: Sensitive to stretching movements and heavy pressure
- Ruffini corpuscles: Sensitive to pressure and pain
Basal layer: The basal layer is the deepest layer of the epidermis, resting on the dermoepidermal junction. It contains melanocytes, Merkel cells, and stem cells of keratinocytes. These stem cells have the ability to self-renew and differentiate into keratinocytes, which is essential for epidermal regeneration.
Stratum corneum: The stratum corneum is the most superficial layer of the epidermis, in direct contact with the outside world. It consists of corneocytes and forms a protective mechanical barrier for the skin. It also plays a role in maintaining the skin's hydration.
Granular layer: The granular layer is one of the sub-layers of the epidermis, located just below the stratum corneum. It is composed of flattened keratinocytes arranged in 3 to 5 layers. These cells contain keratohyalin granules and keratinosomes, which give this layer its granular appearance.
Spiny layer: The spiny layer, or Malpighi layer, is one of the sub-layers of the epidermis, located just above the basal layer. The keratinocytes in this layer have small projections in the shape of spines, which is how this layer got its name. It also contains desmosomes.
Depigmentation: Depigmentation is characterized by the appearance of lighter spots on the skin, lighter than its natural color. It can be caused by various factors, including genetic anomalies in melanogenesis. It can also be intentionally induced by using depigmenting treatments containing hydroquinone or corticosteroids, for example. The latter case is unfortunately common and constitutes a major public health issue in Africa.
Dermatosis: Dermatosis refers to any skin condition or disease. It can have various causes, origins, or locations, and is a very general term. It includes a wide range of skin problems or conditions, such as hyperpigmentation spots, acne, eczema, or urticaria.
Ashy dermatosis: This is a type of dermatosis that is common in children but can also occasionally appear in adults. It is characterized by bluish and/or grayish spots. These spots appear as macules with erythematous borders and typically appear on the upper limbs, chest, and face.
Dermatosis papulosa nigra: This is a dermatosis characterized by the appearance of small seborrheic keratoses localized on the face. It is more commonly found in individuals with dark skin tones.
Dermis: The dermis is a sub-layer of the skin located between the epidermis and the hypodermis. It is divided into two sub-layers: the superficial dermis and the deep dermis. The dermis is composed of fibroblasts, collagen and elastic fibers, blood vessels, glycosaminoglycans, and other structural molecules. It plays a role in support, thermoregulation, wound healing, and hydration.
Eczema: Eczema, or atopic dermatitis, is a chronic inflammatory skin condition. It is characterized by dry skin associated with redness, itching, vesicles, and crusts that flare up in episodes. It typically develops 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. Notably, in black, olive, and mixed skin tones, it can lead to the appearance of hyperpigmentation spots.
Elastin: Elastin is a protein secreted by fibroblasts in the dermis. It forms fibers that assemble into a network. Elastin is partly responsible for the skin's elasticity and extensibility. This is why the skin returns to its original shape after being pinched or stretched. Elastin production occurs during growth and decreases with age, which is a sign of skin aging.
Erythema: Erythema is a dermal lesion characterized by localized or diffuse redness, which varies in intensity and disappears after applying pressure to the area. It is caused by vasodilation of superficial skin blood vessels. Erythema can be triggered by conditions like erythrosis, burns, sunburns, viral or bacterial infections, or insect bites.
Exfoliation: Exfoliation is a key step in skin regeneration. It is a physiological process that allows the skin to remove dead cells from the epidermis. It is worth noting that black, olive, and mixed skin exfoliate 2.5 times more slowly than Caucasian skin. Exfoliation can be done mechanically using scrubs with micrograins or chemically with peels.
Facial Afro-Caribbean Childhood Eruption: This is a granulomatous perioral dermatitis in black children. It is characterized by the appearance of multiple papules on the face. These papules are lupoid to the touch and contain lymphatic fluid.
Fibroblast: Fibroblasts are dermal cells responsible for secreting elastic fibers, collagen fibers, glycosaminoglycans, and growth factors. Their presence is essential because they give the skin its elasticity, firmness, and hydration. As fibroblast activity decreases with age, this contributes to the appearance of skin aging.
Hydrolipidic film: The hydrolipidic film is a superficial layer that covers the entire skin. It is composed of sweat, sebum, and water, and it protects the skin from bacteria and other external aggressions. It serves as a protective barrier for the skin.
Cutaneous flora: Cutaneous flora or skin microbiota refers to the collection of bacteria, viruses, and fungi living in symbiosis on our skin. Found on the epidermis or in the upper part of hair follicles, it forms one of the skin's protective barriers. It helps protect the skin from external threats, bacteria, and other pathogens, and also plays a role in skin regeneration.
Pilosebaceous follicle: The pilosebaceous follicle is the combination of the hair follicle and the sebaceous gland (which secretes sebum). The sebaceous gland is attached to the hair sheath.
Dissecting folliculitis of the scalp: This is a rare and chronic skin condition of the scalp that primarily affects black men. It is characterized by painful inflammatory nodules, pustules, and abscesses, which often lead to the development of scarring alopecia. The causes of this dermatitis are still unknown.
Hair sheath: The hair sheath is an invagination of the epidermis that contains the hair. It consists of the external epithelial sheath, which is an extension of the epidermis made up of epidermal cells that extend into the dermis, and the internal epithelial sheath, which develops from the base of the hair and extends to the sebaceous orifice.
Sebaceous gland: The sebaceous gland is responsible for secreting sebum, which is activated by hormones. It is attached to the hair, and together they form the pilosebaceous follicle.
Hydration: Skin hydration is a key aspect of its functioning, as it constitutes 70% of its composition. Water ingested through drinks enters the bloodstream, diffuses from the dermis to the epidermis, and helps minimize daily water loss, maintaining a constant hydration level. Water also contributes to the composition of the hydrolipidic film, which helps protect the skin from external aggressions.
Acral focal hyperkeratosis: Hyperkeratosis refers to the abnormal and spontaneous thickening of the epidermis. It can occur due to eczema, psoriasis, or repeated localized friction. It is caused by a dysfunction in the regeneration of skin cells.
Hyperpigmentation: Hyperpigmentation is a disorder of melanogenesis. It leads to an overproduction of melanin, resulting in darker skin spots that can be localized or diffuse on the face or body. It can be caused by various factors, including genetics, hormones, UV rays, and can also be post-inflammatory (such as after a pimple or friction). Hyperpigmentation is the most common skin issue encountered in black, olive, and mixed skin tones.
Hypoallergenic: The term hypoallergenic found in many cosmetic products refers to a formulation designed to minimize the risk of allergic reactions when used. This is ensured through pre-clinical and clinical testing.
Hypodermis: The hypodermis is the deepest layer of the skin. It serves as an interface between the dermis and the mobile structures (muscles and tendons). It consists of a rich vascular network, connective and adipose tissues, and protects the body from shocks while maintaining a constant skin temperature.
Ichthyosis: Ichthyosis is a rare, genetically inherited chronic dermatological condition. It is characterized by very dry skin with excessive scales, which may be accompanied by redness, skin cracks, or painful blisters. The name "ichthyosis" comes from the Greek word for fish, as the skin takes on a "fish scale" appearance.
Dermoepidermal junction: The dermoepidermal junction separates the dermis and the epidermis. It contains plaques, proteins, and anchoring filaments that help maintain the cohesion between the dermis and epidermis and act as a barrier and filter for the flow of nutrients between these two layers.
Keratin: Keratin is a fibrous protein rich in sulfur amino acids, insoluble in water, and highly resistant. It is produced by keratinocytes during keratinization. Found in the epidermis, hair, nails, and other appendages, it forms fibers and acts as an intercellular cement, contributing to the protection of the skin against external aggressions by ensuring strong cellular cohesion.
Keratinocytes: Keratinocytes make up 90% of epidermal cells. They originate at the base of the epidermis from stem cells, then migrate and specialize until they reach the stratum corneum and become corneocytes. They are responsible for synthesizing keratin, essential lipids, and NMF (Natural Moisturizing Factor). Their presence is essential for the proper functioning of the skin, as they form a protective barrier that shields it from external threats.
Keratinosome: Keratinosomes, or Odland bodies, are small oval organelles found in keratinocytes of the Malpighi layer. They synthesize keratin, which is essential for the skin.
Palmoplantar keratoderma: Palmoplantar keratoderma is a rare hereditary dermatological condition characterized by hyperkeratosis (thickening of the skin) localized to the palms of the hands and soles of the feet. Other causes may include endocrinological disorders or infections.
Pilar keratosis: Pilar keratosis, or follicular keratosis, is a genetic dermatitis. It is characterized by thick, rough skin with the presence of small bumps, primarily on the arms, thighs, and buttocks. It results from an overproduction of keratin that blocks hair follicles, and no specific treatment is currently available. It most commonly appears during childhood and adolescence and may naturally disappear or persist with age.
Lentigo: Lentigo, or age spots, is a small brown spot, sometimes raised, commonly found on the face, hands, and neck. There are different types: senile lentigo (due to aging) or actinic lentigo (due to sun exposure).
Lichen planus: Lichen planus is a chronic inflammatory dermatological condition that tends to affect adults. It is characterized by purple, scaly skin lesions that are itchy, mainly located on the wrists and ankles. The exact cause is unknown, but it can sometimes appear as a side effect of treatments for conditions such as diabetes or hypertension.
Actinic lichen planus: Actinic lichen planus is a subtype of lichen planus. It appears exclusively on sun-exposed areas such as the face, neck, and backs of the hands. This dermatological condition is more common in hot countries like India, the Maghreb, or East Africa.
Systemic lupus erythematosus (SLE): Lupus erythematosus is a chronic autoimmune dermatitis. It is termed "systemic" when it affects a range of organs, such as the skin, kidneys, heart, etc. It can be triggered by a combination of environmental, genetic, or hormonal factors. Clinically, on the skin, it appears as red patches, predominantly on sun-exposed areas like the nose, around the eyes, and the cheeks, forming a butterfly-shaped mask.
Skin demarcation line or Futcher–Voigt line: These are more or less distinct lines that separate two skin areas with different pigmentation intensities. They are located both on the face and the body and are more visible on black, olive, and mixed skin tones.
Extracellular matrix: The extracellular matrix is a collection of extracellular macromolecules such as collagen and elastin fibers, structural glycoproteins, etc. It is primarily secreted by fibroblasts.
Melanin: Melanin is the natural pigment that gives the skin, hair, and eyes their color. In the skin, it is synthesized by melanocytes in the melanosomes, and there are two types: pheomelanin (a red, carcinogenic and yellow pigment) and eumelanin (a black and brown pigment with photo-protective properties).
Melanocyte: Melanocytes are epidermal cells responsible for synthesizing melanin. Once synthesized, they transfer melanosomes filled with melanin to keratinocytes through their filaments. Present in the epidermis, as well as in hair follicles and the eye, melanocytes give each person their natural skin color.
Melanogenesis: Melanogenesis is the process of melanin synthesis. It occurs in melanocytes, particularly in their organelles called melanosomes. The synthesis begins with Dopaquinone, creating two types of melanin: pheomelanin and eumelanin. Once formed, melanosomes are transferred to keratinocytes to provide the skin with its natural color. Any disruption in this process can lead to hypopigmentation (white spots) or hyperpigmentation (dark spots).
Melanoma: Melanoma, or malignant melanoma, is a type of skin cancer that develops from melanocytes. It presents as pigmented spots that transform into nodules or moles. Factors that contribute to its development include genetics, sun exposure, skin phototype, and the presence of pre-existing moles. Timely treatment is important to prevent the spread of cancerous cells to distant organs, such as the lungs or liver.
Transient neonatal pustular melanosis: This is a benign dermatological condition that primarily affects black skin. It is characterized by the appearance of pustular vesicles that rapidly evolve into small pigmented macules that persist for a few weeks to months.
Melasma: Melasma, also known as the "pregnancy mask," is a dermatological condition that typically affects pregnant women but can also occur with contraception. It is characterized by hyperpigmentation of the skin, especially on areas exposed to the sun, such as the cheeks, forehead, and nose. It is partly caused by overproduction of endogenous hormones related to pregnancy or contraception, excessive sun exposure without protection, or an adverse reaction to medication.
Arrector pili muscle: The arrector pili muscle is a smooth muscle in the skin. It is attached to the base of the hair follicle and extends to the epidermis. It responds to various stimuli and causes the hair to stand upright during contraction.
NMF (Natural Moisturizing Factor): The Natural Moisturizing Factor is composed of amino acids, lactic acid, urea, sugars, minerals, and other skin elements. Present in the stratum corneum, it helps maintain hydration in the epidermis. Thanks to its hygroscopic and hydrosoluble properties, it can capture and retain water in the skin.
Ochronosis: Ochronosis is a skin complication related to the long-term use of depigmenting treatments containing hydroquinone or corticosteroids. It results in the appearance of diffuse hyperpigmented spots on the face or body, which may become raised and granulose.
Dermal papilla: Dermal papillae are extensions of dermal cells that interlock with the epidermal ridges at the dermoepidermal junction. In contact with the dermal capillaries, they facilitate the transfer of nutrients and oxygen to the epidermis via diffusion.
Skin: The skin is an organ that functions to cover the entire body, protecting it from external threats and pathogens, maintaining a constant body temperature, and producing vitamin D. Its size and thickness vary from one individual to another and from one body area to another (e.g., eyelids and palms). The skin is divided into layers: the epidermis (the outermost), the dermoepidermal junction, the dermis, and the hypodermis (the deepest).
Photosensitization: Photosensitizing refers to the formulation of cosmetic products, medications, or other substances that increase the skin's sensitivity to UV rays from the sun. This heightened sensitivity leads to skin issues (such as burns or spots) more rapidly.
Phototype: Phototype is a classification used to assess the risk of a skin reaction when exposed to sunlight, depending on the individual's skin sensitivity. It takes into account four factors: skin color, tanning type, frequency of sunburn, and hair color. There are six phototypes, ranging from fair to dark skin. Knowing your phototype is important for adopting a skincare routine suited to your skin’s needs and risks.
Anchoring plaques: Anchoring plaques are a set of anchoring fibers made of type VII collagen. Positioned in the fibrillar zone of the dermis, they are part of the dermoepidermal junction. Their presence is crucial for ensuring good cohesion between the dermis and epidermis.
Ingrown hair: An ingrown hair, or beard folliculitis, occurs when a hair that should grow out of the skin continues to grow beneath the skin. This leads to the formation of inflamed and painful pimples. This skin condition is common among people with black skin because of the curly nature of their hair (which may grow in a "corkscrew" pattern) and slightly thicker skin. However, it can be exacerbated by improper shaving or waxing.
Pores: Pores are small openings in the skin’s surface that are connected to the pilosebaceous follicles (the hair follicle and sebaceous glands). Through these pores, hair grows, and sebum, sweat, dead skin cells, and other substances are released.
Prurigo: Prurigo is a dermatological condition characterized by the appearance of pruritic lesions (papules, nodules, plaques, etc.) that cause intense itching. These can be acute (lasting less than six weeks) or chronic. It most often affects children and can result from allergic reactions, insect bites, or other causes.
Psoriasis: Psoriasis is a chronic dermatological condition characterized by red patches covered with scales. It most often develops on the elbows, knees, and scalp. It can be genetically related to an abnormally fast turnover of skin cells, but it can also be triggered by stress, hormones, or certain medications.
Skin regeneration: Skin regeneration, or cellular turnover, refers to the process by which the skin renews itself. It eliminates dead or damaged cells due to external aggressions and synthesizes new cells in a continuous 28-day cycle. Additionally, it rehydrates, reoxygenates, and nourishes itself.
Wrinkle: A wrinkle is a more or less deep groove on the surface of the skin. There are different types based on their causes:
- Dehydration wrinkles are reversible and appear when the skin is dehydrated.
- Expression wrinkles are caused by repeated muscle contractions responsible for facial expressions.
- Age-related wrinkles are a sign of skin aging, associated with loss of elasticity and firmness.
Rosacea: Rosacea is a chronic dermatological condition that causes vasodilation of small blood vessels in the face. It most commonly affects the cheeks, forehead, or nose and results in redness or couperose. It may be triggered by thermal changes (seasonal changes, hot-cold alternations, hot baths, etc.), inflammatory reactions, or genetic predisposition.
Sarcoidosis: Sarcoidosis is a lung condition that can also affect the skin. It appears as painful, red, subcutaneous nodules, often accompanied by a persistent fever.
Sebum: Sebum is a greasy substance made of lipids. It is secreted by the sebaceous glands at the base of the hair follicle and flows to the surface of the skin through pores. It is vital for the skin's function as it forms part of the hydrolipidic film. It helps the skin defend against external threats and maintain constant hydration levels. It is important to know your sebum levels to determine your skin type and create a skincare routine that meets your skin's needs.
Skin sensitivity: The skin contains a significant nervous system that enables it to react to various stimuli such as cold, heat, pain, etc. Sensitivity thresholds vary between individuals, explaining why skin reactions to these stimuli can differ from one person to another.
Scales: Scales refer to thin flakes of corneocytes (skin cells) that detach from the epidermis. Naturally, they are eliminated daily through desquamation and are invisible. However, excessive elimination, such as after significant sun exposure or a dermatological condition like psoriasis, can make them visible, forming a white "peeling" layer on the skin.
Hives: Hives (urticaria) is an inflammatory skin condition characterized by red papules or edema, causing intense itching. Depending on its duration, it can be acute or chronic. It is often caused by allergies (to food, medications, dust, etc.), insect bites, or diseases such as rheumatoid arthritis.
Chickenpox: Chickenpox is a highly contagious viral disease (varicella-zoster virus, VZV). It is characterized by the appearance of vesicular rashes, itching, and redness. It primarily affects children but can also affect adults. It usually heals in about 10 days unless complications arise (such as pulmonary involvement, secondary bacterial infections, or Reye’s syndrome).
Venule: A venule is a small visible vein under the skin that carries waste products from the skin back to the heart.
Skin aging: Skin aging is clinically characterized by thinner, softer, duller, rougher, drier skin with wrinkles and age spots. It is inevitable as it is determined by our genetics from birth, but it can be accelerated by environmental factors, sun exposure, smoking, hormonal deficiencies, and inappropriate skincare.
Vitiligo: Vitiligo is a benign, acquired skin condition characterized by the appearance of white patches on the skin. It is caused by the progressive loss of melanocytes that normally synthesize melanin (the pigment responsible for skin color). Their destruction is believed to be an autoimmune process. This condition is particularly noticeable on ethnic skin due to the stark contrast between the white patches and natural skin color, which can cause significant psychological impact.
Xerosis: Xerosis refers to excessive skin dryness. It is characterized by the appearance of scales, often described as "crocodile skin" or "fish scales," and is accompanied by tightness and/or itching. It occurs when the skin is dehydrated and lacks lipids. It can be genetic or caused by the use of skincare products that do not meet the skin's needs, or after prolonged exposure to cold, heat, or wind.