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Facts about the skin from DermNet New Zealand Trust. Topic index: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z


Glossary of dermatological terms

If you don't find what you are looking for in this alphabetical list of dermatological terms, try DermNet NZ'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.
Abscess
Acral
Acral distribution of a dermatosis means it affects distal portions of limbs (hand, foot) and head (ears, nose).
Erythema multiforme
Adipose cells
Adipose cells or lipocytes are grroups of fat cells forming yellow lobules in subcutaneous tissue.
Skin structure
Anagen
Anagen is the growth phase of the hair cycle. Anagen hair has a pointed tip and grows over several years.
Hair cycle
Annular
Annular distribution refers to lesions grouped in a circle.
Annular eruption
Aplasia
Aplasia refers to tissue that has failed to grow, as in aplasia cutis (illustrated).
Aplasia cutis
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.
Fox-Fordyce disease
Appendages
The epidermal appendages include eccrine (sweat) glands, apocrine (scent) glands, pilosebaceous structures (hair and oil glands) and nails.
Skin structure
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).
Goose bumps
Atrophy
Atrophy occurs when some component of the skin has shrunk.
Cutaneous atrophy
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.
Epidermis
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 lines
Blaschko lines follow a roughly linear, segmental pattern described by Blaschko. Many birthmarks appear to be distributed within these segments.
Blaschko lines
Bulla
A bulla is a large fluid-filled blister greater than 1 cm in diameter. It may be a single compartment or multiloculated. The adjective is ‘bullous’.
Bulla
Carcinoma
Carcinoma refers to cancer made up of malignant epithelial cells (e.g. basal cell carcinoma, illustrated).
Basal cell carcinoma
Catagen
Catagen is a short involutional phase of the hair cycle.
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.
Skin structure
Crusting
Crust occurs when plasma exudes through an eroded epidermis and dries on the skin surface. It is rough on the surface and is yellow or brown in colour. Bloody crust appears red, purple or black.
Crusting
Cyst
A cyst is a papule or nodule that contains fluid or semi-fluid material so is fluctuant.
Cyst
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).
Herpes zoster
Dermatosis
Dermatosis is another name for for skin disease.
Dermatosis
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.
Skin structure
Desmosomes
Desmosomes are the structures that stick adjacent keratinocytes tightly together, rather like cement between bricks.
Epidermis
Desquamation
Desquamation is the term given to skin coming off in scales or peeling.
Exfoliation
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.
Dysplastic naevi
Dystrophy
Dystrophy refers to degeneration or abnormal formation of the skin. It is often used to refer to nail diseases.
Nail dystrophy
Ecchymoses
Ecchymoses are bruises.
Ecchymoses
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).
Hyperhidrosis
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.
Epidermis
Epithelium
Epithelium is a tissue composed of packed cells that line a body surface internally (e.g. mouth) or externally (e.g. skin).
Epithelium
Erosion
Erosion is caused by loss of the surface (epidermis) of a skin lesion; it is a shallow moist or crusted lesion.
Erosions
Erythema
Erythema is the name given to red skin due to increased blood supply and may be applied to any red coloured dermatosis.
Erythema
Erythroderma
Erythroderma occurs when a skin condition affects the whole body or nearly the whole body, which is red all over.
Erythroderma
Eschar
Dark-coloured adherent crust of dead tissue found on some ulcers.
Excoriation
An excoriation is a scratch mark or surface injury penetrating the dermis. It may be linear or a picked scratch (prurigo). Excoriations may occur in the absence of a primary dermatosis.
Excoriations
Exfoliation
Exfoliation refers to peeling skin.
Exfoliation
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.
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).
Filiform wart
Fissure
A fissure is a thin crack within epidermis or epithelium, and is due to excessive dryness.
Fissures
Flexural distribution
Flexural distribution of a dermatosis involves the flexures, i.e. the body folds. This is also known as intertriginous distribution.
Infantile seborrhoeic dermatitis
Follicular
Follicular distribution of a dermatosis refers to individual lesions arisin from hair follicles, e.g. acne. These may be grouped into confluent plaques.
Folliculitis
Fungating
Refers to a large malignant tumour that is erupting like a mushroom or fungus.
Fungating lesion
Furfuraceous
Description of scale in which is is bran-like or powdery.
Furfuraceous scale
Granular layer
The granular layer of the epidermis (stratum granulosum) is characterised by flattened cells filled with dark granules containing keratohyaline protein.
Epidermis
Granulation tissue
Granulation tissue is a made of a mass of new capillaries and fibrous tissue in a healing wound.
Granulation tissue
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).
Granuloma annulare
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.
Gyrate rash
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 bulb
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.
Hair cycle
Hemidesmosomes
Hemidesmosomes are the structures that stick basal keratinocytes tightly to the dermis via the basement membrane.
Epidermis
Herpetiform
A herpetiform eruption means it looks like a herpes infection, with grouped umbilicated vesicles.
Herpes zoster
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.
Epidermis
Hyperkeratosis
Hyperkeratosis or scaling is an increase in the dead cells on the surface of the skin (stratum corneum).
Psoriasis
Hyperpigmentation
Hyperpigmentation may be due to hypermelanosis or haemosiderin deposits that result in skin colour that is darker than normal.
Melasma
Hyperplasia
Hyperplasia is the enlargement of a tissue by an increase in cell numbers.
Pseudoepitheliomatous hyperplasia
Hypertrophy
Some component of the skin such as a scar is enlarged or has grown excessively.
Keloid
Hypopigmentation
Hypopigmentation refers to skin colour that is paler than normal.
Pityriasis versicolor
Iatrogenic
Iatrogenic illness is caused by a doctor's actions, for example a rash due to prescription of a medicine.
Drug rash
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.
Induration due to cancer
Infarcts
Infarcts are due to interrupted blood supply and result in black areas of necrotic (dead) tissue or dry gangrene.
Isomorphic phenomenon
The isomorphic or Koebner phenomenon refers to the tendency of several skin conditions to affect areas subjected to injury.
Psoriasis
Keratin
The protein produced by keratinocytes, forming the bulk of epidermis, hair and nails.
Fingernail
Keratinocytes
Keratinocytes are the cells that make up the ‘brick wall’ of the epidermis. They produce a protein called keratin.
Epidermis
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.
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.
Epidermis
Lesion
A lesion is any single area of altered skin. It may be solitary or multiple.
Lesion
Leukoderma
Leukoderma means white skin. Also known as achromia.
Vitiligo
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.
Lichenification
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).
Lichen planus
Linear lesion
A linear shape to a lesion often occurs for some external reason such as scratching. Also striate.
Linear lesion
Lipocytes
Lipocytes or adipose cells are groups of fat cells forming yellow lobules in subcutaneous tissue.
Skin structure
Maceration
Maceration describes moist peeling skin.
Athlete's foot
Macule
A macule is a small area of colour change, often defined as less than 1.5 cm diameter.
The surface is smooth.
Macule
Melanin
Melanin is the brown coloured protein made by melanocytes.
Melanoma
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.
Epidermis
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.
Mucosa
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.
Normal nail
Nikolsky sign
Nikolsky sign is positive when slight rubbing of the skin results in exfoliation of the skin's outermost layer.
Positive Nikolsky sign
Nodule
A nodule is an enlargement of a papule in three dimensions (height, width, length). It is a solid lesion more than 1 cm in diameter.
Nodule
Nummular lesion
Round (coin-shaped) lesions. Also known as discoid.
Nummular lesion
Oedema
Oedema refers to tissue swelling (American spelling ‘edema’)
Oedema
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.
Skin structure
Papule
Papules are small palpable lesions. The usual definition is that they are less than 1 cm diameter. They are raised above the skin surface, and may be solitary or multiple.
Papule
Patch
A patch refers to a large area of colour change, with smooth surface.
Patch
Pathergy
The isomorphic phenomenon resulting in ulceration i.e. ulcers appearing at the sites of minor trauma such as venepuncture (blood test).
Pathergy in Behcet syndrome
Pedunculated
Pedunculated means a lesion has a peduncle or is on a stalk.
Skin tag
Perioral
Perioral distribution means the dermatosis is around the mouth. Also ‘periocular’, ‘perianal’ and so forth.
Perioral dermatitis
Petechiae
Petechiae are small red, purple or brown spots - a form of purpura.
Petechiae
Pilosebaceous structures
The pilosebaceous structures contain hair and sebaceous glands (oil glands).
Skin structure
Pityriasis
Pityriasis refers to a skin condition with a bran-like powdery scale.
Pityriasis
Plaque
A plaque is a palpable flat lesion usually greater than 1 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. The name 'plaque' is derived from the French word for plate.
Plaque
Poikiloderma
Poikiloderma is skin with a variegated appearance, usually mixed pallor, telangiectasia & pigmentation.
Poikiloderma
Polygonal
A polygonal skin lesion means it has a non-geometric shape.
Erythema
Polymorphic
A polymorphic eruption means the lesions may have varied shapes.
Lichen planus
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.
Epidermis
Purpura
Purpura is bleeding into the skin. This may be as petechiae or ecchymoses. Purpura does not blanch with pressure (diascopy).
Purpura
Pustule
A pustule is a collection of pus. It is filled with neutrophils, and may be white, or yellow. Not all pustules are infected.
Pustule
Rash
A rash is a widespread eruption of lesions.
Rash
Reticular dermis
The reticular dermis is the lower portion of the dermis. It is composed of coarse elastic fibres and thick collagen bundles parallel to the skin surface.
Skin structure
Scaling
Scaling or hyperkeratosis is an increase in the dead cells on the surface of the skin (stratum corneum). Scale can be described as furfuraceous or pityriasiform (bran-like), psoriasiform (psoriasis-like), hyperkeratotic (thick), adherent or minimal.
Scaling
Sclerosis
Hardened scar-like or indurated tissue as in localised scleroderma.
Generalised morphoea
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.
Skin structure
Serpiginous
A serpignous lesion is in the shape of a snake or serpent.
Larva migrans
Sessile
Sessile skin lesions appear to be stuck directly onto the skin surface without a stalk.
Seborrhoeic keratosis
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.
Epidermis
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.
Epidermis
Stratum granulosum
This is the granular layer of the epidermis is characterised by flattened cells filled with dark granules containing keratohyaline protein.
Epidermis
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.
Epidermis
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.
Skin structure
Target lesion
Concentric rings like a dartboard. Also known as iris lesion.
Target lesions
Telangiectasia
Telangiectasia is the name given to prominent cutaneous blood vessels. They are red or purple in colour.
Telangiectasia
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).
Hair cycle
Ulcer
An ulcer is full thickness loss of epidermis or epithelium and dermis and may involve subcutaneous tissue. An ulcer heals with a scar. It may be covered with an eschar.
Ulcers
Umbilicated
Umbilicated papules or vesicles have a central dell, such as is seen with molluscum contagiosum or herpes simplex infections.
Molluscum contagiosum
Venulectasia
Venulectasia is the name given to prominent venules, blue in colour and often on the lower legs.
Venulectasia
Verrucous
Verrucous means wart-like, ie. thickened and scaly.
Viral warts
Vesicle
Vesicles are small fluid-filled blisters less than 1cm in diameter. They may be single or multiple. The fluid may be clear or blood-stained.
Vesicles
Weal
A weal, also spelled ‘wheal’ is an oedematous papule or plaque caused by swelling in the dermis. Wealing indicates urticaria or an urticaria-like condition.
Weal
Wood light
Wood lamp emits long wavelength UVA used to examine the skin pigmentary changes and fluorescent infections such as cat ringworm.
Wood's light

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