Glossary of dermatological terms

If you don't find what you are looking for in this alphabetical list of dermatological terms, try DermNet's dermatopathological glossary, the A-Z page index or search box, or the Online Medical Dictionary.

Abscess An abscess is a localised collection of pus.
Acral Acral distribution of a dermatosis means it affects distal portions of limbs (hand, foot) and head (ears, nose).
Adipose cells Adipose cells or lipocytes are grroups of fat cells forming yellow lobules in subcutaneous tissue.
Anagen Anagen is the growth phase of the hair cycle. Anagen hair has a pointed tip and grows over several years.
Annular Annular distribution refers to lesions grouped in a circle.
Aplasia Aplasia refers to tissue that has failed to grow, as in aplasia cutis (illustrated).
Apocrine glands Apocrine glands are scent glands found most profusely in armpits and groins. They become active after puberty. Apocrine sweat is thick and odourless; the smell derives from bacterial colonisation.
Appendages The epidermal appendages include eccrine (sweat) glands, apocrine (scent) glands, pilosebaceous structures (hair and oil glands) and nails.
Arrector pili muscles Arrector pili muscles originate near the basement membrane zone and attach to the hair follicle near its base. They cause erection of the hairs on exposure to cold or fear (goose bumps).
Atrophy Atrophy occurs when some component of the skin has shrunk.
Basal layer The basal layer is the columnar or rectangular cells at the bottom of the epidermis from which new cells are continuously produced. Scattered melanocytes are normally found in this layer.
Basement membrane zone The basement membrane zone separates the epidermis from the dermis. Its components include the selectively permeable basal cell membrane, lamina lucida containing anchoring filaments, lamina densa and sublamina densa (bound to the dermis).
Blaschko's lines Blaschko's lines follow a roughly linear, segmental pattern described by Blaschko. Many birthmarks appear to be distributed within these segments.
Bulla A bulla is a large fluid-filled blister. It may be a single compartment or multiloculated. The adjective is ‘bullous’.
Carcinoma Carcinoma refers to cancer made up of malignant epithelial cells (e.g. basal cell carcinoma, illustrated).
Catagen Catagen is a short involutional phase of the hair cycle.
Collagen Collagen is the structural protein making up the bulk of the dermis. It is produced by fibroblasts. It is composed of a triple helix of strong fibres.
Configuration Configuration refers to the shape or outline of the skin lesions. Skin lesions are often grouped together. The pattern or shape may help in diagnosis as many skin conditions have characteristic configuration.
Connective tissue Connective tissue of the skin refers to dermis and subcutaneous tissue.
Crusting Crust occurs when plasma exudes through an eroded epidermis. It is rough on the surface and is yellow or brown in colour. Bloody crust appears red, purple or black.
Cyst A cyst is a papule or nodule that contains fluid or semi-fluid material so is fluctuant.
Dendritic cells Dendritic cells are cells with long finger-like processes (dendrites), and include melanocytes, Langerhans cells and some tissue macrophages (immune cells).
Dermatologist The medical specialist in diseases of skin, hair and nails. Refer to DermNet's pages, What is a Dermatologist.
Dermatology The study of skin, hair and nails.
Dermatomal Corresponding with nerve root distribution (dermatome), as seen with the blistering rash herpes zoster (shingles, illustrated).
Dermatosis Dermatosis is another name for for skin disease.
Dermis The dermis is the middle connective tissue layer of skin, composed of collagen and elastin fibres, blood vessels, nerves and inflammatory cells in a ground substance gel.
Desmosomes Desmosomes are the structures that stick adjacent keratinocytes tightly together, rather like cement between bricks.
Desquamation Desquamation is the term given to skin coming off in scales or peeling.
Distribution The distribution of a dermatosis refers to how the skin lesions are scattered or spread out. Skin lesions may be isolated (solitary or single) or multiple. The localisation of multiple lesions in certain regions helps diagnosis, as skin diseases tend to have characteristic distributions. What is the extent of the eruption and its pattern?
Dysplasia Dysplasia means abnormal development of a cell or tissue. ‘Dysplastic naevi’ are atypical moles (illustrated), and are variously defined.
Dystrophy Dystrophy refers to degeneration or abnormal formation of the skin. It is often used to refer to nail diseases.
Ecchymoses Ecchymoses are bruises.
Eccrine glands Eccrine glands are found deep in the dermis. They produce sweat, a weak solution of water, salt and waste products, which is excreted into a coiled duct that opens directly onto the skin surface. They are most dense on palms, soles, armpits and forehead. Excessive sweating is known as hyperhidrosis (illustrated).
Elastin Elastin is the protein making up thin elastic fibres. These are produced by fibroblasts. They return deformed skin to its resting position.
Epidermis The epidermis is the outer epithelial layer of the skin, and is mainly composed of keratinocytes.
Epithelium Epithelium is a tissue composed of packed cells that line a body surface internally (e.g. mouth) or externally (e.g. skin).
Erosion Erosion is caused by loss of the surface of a skin lesion; it is a shallow moist or crusted lesion.
Erythema Erythema is the name given to red skin due to increased blood supply and may be applied to any red coloured dermatosis.
Erythroderma Erythroderma occurs when a skin condition affects the whole body or nearly the whole body, which is red all over.
Excoriation An excoriation is a scratch mark. It may be linear or a picked scratch (prurigo). Excoriations may occur in the absence of a primary dermatosis.
Exfoliation Exfoliation refers to peeling skin.
Extensor distribution Extensor distribution of a dermatosis involves the extensor surfaces of limbs, i.e. the outer arm or the front of the leg, as is often the case with psoriasis.
Felon A felon is an abscess in the pulp of any digit.
Fibroblasts Fibroblasts are cells found in the dermis that produce collagen, elastin, ground substance and fibronectin (a glycoprotein).
Filiform Filiform means thread-like as in ‘filiform wart’ (illustrated).
Fissure A fissure is a thin crack within epidermis or epithelium, and is due to excessive dryness.
Flexural distribution Flexural distribution of a dermatosis involves the flexures, i.e. the body folds. This is also known as intertriginous distribution.
Follicular Follicular distribution of a dermatosis refers to individual lesions arisin from hair follicles, e.g. acne. These may be grouped into confluent plaques.
Fungating Refers to a large malignant tumour that is erupting like a mushroom or fungus.
Granular layer The granular layer of the epidermis (stratum granulosum) is characterised by flattened cells filled with dark granules containing keratohyaline protein.
Granulation tissue Granulation tissue is a made of a mass of new capillaries and fibrous tissue in a healing wound.
Granuloma A granuloma is a histological (pathological) term refering to chronic inflammation in which there are several types of inflammatory cells including giant cells. Granulomas form in response to foreign bodies, certain infections (tuberculosis, leprosy) and inflammatory skin diseases (granuloma annulare [illustrated], granuloma faciale, sarcoidosis).
Ground substance Ground substance is the gel component of the dermis. It contains hyaluronic acid, dermatan sulphate, & chondroitin-6-sulphate (these are anionic polysaccharides or glycosaminoglycans).
Gyrate rash A rash that appears to be whirling in a circle.
Hair A specialised epidermal product of the pilosebaceous structure. Terminal hair is found on the scalp and vellus hair on body surface (short, thin, light coloured). Structure of the hair bulb is illustrated.
Hair cycle The hair cycle has a growth phase (anagen) when the hair has a pointed tip, which lasts several years; a short involutional phase (catagen); and a resting phase with clubbed or bulbous tip (telogen), which lasts for several months.
Hemidesmosomes Hemidesmosomes are the structures that stick basal keratinocytes tightly to the dermis via the basement membrane.
Herpetiform A herpetiform eruption means it looks like a herpes infection, with grouped umbilicated vesicles.
Horny layer The horny layer of the epidermis (stratum corneum) consists of stacks of dead cells without nuclei make up the dry or keratinised stratum corneum. The top layer of cells loosens and falls off.
Hyperkeratosis Hyperkeratosis or scaling is an increase in the dead cells on the surface of the skin (stratum corneum).
Hyperpigmentation Hyperpigmentation may be due to hypermelanosis or haemosiderin deposits that result in skin colour that is darker than normal.
Hyperplasia Hyperplasia is the enlargement of a tissue by an increase in cell numbers.
Hypertrophy Some component of the skin such as a scar is enlarged or has grown excessively.
Hypopigmentation Hypopigmentation refers to skin colour that is paler than normal.
Iatrogenic Iatrogenic illness is caused by a doctor's actions, for example a rash due to prescription of a medicine.
Immune cells Immune cells found in the skin include Langerhans cells in the epidermis. Dermal immune cells are composed of lymphocytes, neutrophils, monocytes (histiocytes & activated macrophages) and mast cells. They are most often found around blood vessels. Immune cells are recruited in great numbers to heal wounds and fight infection. Many skin diseases are characterised by specific patterns of these cells.
Induration Induration is skin that feels hard and thickened.
Infarcts Infarcts are due to interrupted blood supply and result in black areas of necrotic (dead) tissue or dry gangrene.
Isomorphic phenomenon The isomorphic phenomenon refers to the tendency of several skin conditions to affect areas subjected to injury.
Keratin The protein produced by keratinocytes, forming the bulk of epidermis, hair and nails.
Keratinocytes Keratinocytes are the cells that make up the ‘brick wall’ of the epidermis. They produce a protein called keratin.
Koebner phenomenon The Koebner or isomorphic phenomenon refers to the tendency of several skin conditions to affect areas subjected to injury. Koebnerised lesions are often linear in shape. The illustration is of koebnerised psoriasis.
Langerhans cells Langerhans cells are dendritic cells that present antigens to the immune system. They are found in the prickle cell layer of the epidermis.
Lesion A lesion is any single area of altered skin. It may be solitary or multiple.
Leukoderma Leukoderma means white skin. Also known as achromia.
Lichenification Lichenification is caused by chronic rubbing, which results in palpably thickened skin with increased skin markings and lichenoid scale. It occurs in chronic atopic eczema and lichen simplex.
Lichenoid A lichenoid skin eruption is one that resembles lichen planus. It usually has a tight adherent scale. This term also refers to a particular pattern of inflammation seen on histology (pathological examination).
Linear lesion A linear shape to a lesion often occurs for some external reason such as scratching. Also striate.
Lipocytes Lipocytes or adipose cells are groups of fat cells forming yellow lobules in subcutaneous tissue.
Maceration Maceration describes moist peeling skin.
Macule A macule is a small area of colour change, often defined as less than 1.5 cm diameter. The surface is smooth.
Melanin Melanin is the brown coloured protein made by melanocytes.
Melanocytes Pigment cells normally found in the basal layer of the epidermis. They produce a protein called melanin that protects the skin from damage due to ultraviolet radiation. Benign melanocytic tumours are often called moles. Cancerous melanocytic tumours are called malignant melanoma.
Merkel cells Merkel cells are sensory cells found in the epidermis. Their exact function is uncertain. The Merkel cell carcinoma is a rare form of skin cancer.
Metaplasia Metaplasia is a condition where one type of cell transforms into another type of cell, because of a changed environment.
Morphology Morphology is the form or structure of an individual skin lesion.
Mucosa The mucosa or mucous membrane is a moist lining of internal areas that opens onto the skin surface, e.g. mouth, nose, eyes, genital tissues.
Nails The nail plate is composed of horny cells containing keratin and is produced by nail matrix. Fingernails grow 0.1mm per day; toenails 0.03mm per day.
Nodule A nodule is an enlargement of a papule in three dimensions (height, width, length). It is a solid lesion.
Nummular lesion Round (coin-shaped) lesions. Also known as discoid.
Oedema Oedema refers to tissue swelling (American spelling ‘edema’)
Papillary dermis The papillary dermis is the upper portion of the dermis just beneath the epidermis. It is characterised by thin haphazardly arranged collagen fibres, thin elastic fibres and ground substance.
Papule Papules are small palpable lesions. The usual definition is that they are less than 0.5 cm diameter, although some authors allow up to 1.5 cm. They are raised above the skin surface, and may be solitary or multiple.
Patch A patch refers to a large area of colour change, with smooth surface.
Pathergy The isomorphic phenomenon resulting in ulceration i.e. ulcers appearing at the sites of minor trauma such as venepuncture (blood test).
Pedunculated Pedunculated means a lesion has a peduncle or is on a stalk.
Perioral Perioral distribution means the dermatosis is around the mouth. Also ‘periocular’, ‘perianal’ and so forth.
Petechiae Petechiae are small red, purple or brown spots - a form of purpura.
Pilosebaceous structures The pilosebaceous structures contain hair and sebaceous glands (oil glands).
Pityriasis Pityriasis refers to a skin condition with a bran-like powdery scale.
Plaque A plaque is a palpable flat lesion greater than 0.5 cm diameter. Most plaques are elevated, but a plaque can also be a thickened area without being visibly raised above the skin surface. They may have well-defined or ill-defined borders.
Poikiloderma Poikiloderma is skin with a variegated appearance, usually mixed pallor, telangiectasia & pigmentation.
Polygonal A polygonal skin lesion means it has a non-geometric shape.
Polymorphic A polymorphic eruption means the lesions may have varied shapes.
Prickle cell layer The prickle cell layer of the epidermis (stratum spinosum or spinous cell layer) is so-called because prominent adherence plates (desmosomes) look spiny. The keratinocytes become increasingly flat as they mature and move upwards towards the skin surface.
Purpura Purpura is bleeding into the skin. This may be as petechiae or ecchymoses. Purpura does not blanch with pressure (diascopy).
Pustule A pustule is a purulent vesicle. It is filled with neutrophils, and may be white, or yellow. Not all pustules are infected.
Rash A rash is a widespread eruption of lesions.
Reticular dermis The papillary dermis is the lower portion of the dermis. It is composed of coarse elastic fibres and thick collagen bundles parallel to the skin surface.
Scaling Scaling or hyperkeratosis is an increase in the dead cells on the surface of the skin (stratum corneum).
Sclerosis Hardened scar-like tissue.
Sebaceous glands Sebaceous glands produce an oily substance known as sebum. They are most concentrated on scalp & face where circulating androgens induce increased secretion at puberty. They mostly open into the outer portion of hair follicle and directly onto skin surface on breast and genitals.
Serpiginous A serpignous lesion is in the shape of a snake or serpent.
Sessile Sessile skin lesions appear to be stuck directly onto the skin surface without a stalk.
Squamous cells Squamous cells are flat epithelial cells found on the skin surface. The structure of skin is described as a stratified squamous epithelium, referring to the way the cells are built up in layers.
Stratum corneum The horny layer consisting of stacks of dead cells without nuclei make up the dry or keratinised stratum corneum. The top layer of cells loosens and falls off.
Stratum granulosum This is the granular layer of the epidermis is characterised by flattened cells filled with dark granules containing keratohyaline protein.
Stratum spinosum This is the prickle cell layer of the epidermis, which contains increasingly flat keratinocytes that arise as the epidermal cells mature and move upwards towards the skin surface. They are also called spinous cells.
Subcutaneous tissue Subcutaneous tissue or subcutis is the bottom layer of he skin and is composed of fat cells (adipose cells or lipocytes), connective tissue, blood vessels and nerves.
Target lesion Concentric rings like a dartboard. Also known as iris lesion.
Telangiectasia Telangiectasia is the name given to prominent cutaneous blood vessels. They are red or purple in colour.
Telogen Telogen is the resting phase of the hair cycle. Telogen hairs have a clubbed or bulbous tip and last for several months before falling out (shedding).
Ulcer An ulcer is full thickness loss of epidermis or epithelium. It may be covered with a dark-coloured crust called an eschar.
Umbilicated Umbilicated papules or vesicles have a central dell, such as is seen with molluscum contagiosum or herpes simplex infections.
Venulectasia Venulectasia is the name given to prominent venules, blue in colour and often on the lower legs.
Verrucous Verrucous means wart-like, ie. thickened and scaly.
Vesicle Vesicles are small fluid-filled blisters less than 0.5cm diameter. They may be single or multiple.
Weal A weal, also spelled ‘wheal’ is an oedematous papule or plaque caused by swelling in the dermis. Wealing often indicates urticaria.
Wood's light Wood's light is a lamp emitting long wave UVA used to examine the skin pigmentary changes and fluorescent infections such as cat ringworm.