logo

DermNet NZ


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 Merriam-Webster free online Medical Dictionary.

Abscess
An abscess is a localised collection of pus.
Abscess
Acanthosis
Acantholysis is a histological term referring to thickening of the epidermis.
Acantholysis
Acantholysis is a histological term referring to "floating" skin cells that have lost normal cell-to-cell connections.
Darier disease pathology
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 groups of fat cells forming yellow lobules in subcutaneous adipose 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
Anterior
Anterior location means on the front surface of a body part (ventral).
ANCA
ANCA is an acronym for antineutrophil cytoplasmic antibody, found in some forms of systemic vasculitis.
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
Apoptosis
Apoptosis is the process by which a cell undergoes self destruction.
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
Asymmetrical
Asymmetrical means each side is different from the other.
Atrophie blanche
Atrophie blanchea describes atrophic porcelain-white scars.
Atrophy
Atrophy occurs when some component of the skin has shrunk.
Cutaneous atrophy
Autoimmune reaction
In an autoimmune reaction, the body may destroy its own tissue, which it perceives as foreign.
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).
Benign
Benign means mild, harmless, or having good prognosis.
Bilateral
Bilateral disorders affect both sides of the body.
Biopsy
Biopsy is a tissue sample. The histopathological examination of skin biopsies is essential for the diagnosis of many skin diseases.
Blaschko lines
Blaschko lines follow a roughly linear, segmental pattern described by Blaschko. Many birthmarks appear to be distributed within these segments.
Blaschko lines
Brachy-
Short as in brachyonychia, short nail.
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
Bull's eye
A bull's eye appearance refers to concentric red rings. Also called target or iris lesion.
Burrow
A burrow is a sign of scabies, most often found on wrists and between fingers. It is a skin coloured, snake-like, scaly line about 1 mm in width and 3 to 10 mm in length.
Cancer
A cancer is a malignant tumour, in which there is unlimited cell proliferation and destruction of local tissue. Many cancers also spread through lymphatics and blood vessels (metastasis).
Caudal
Caudal location means on or near to the tail or base of the spine.
Carcinoma
Carcinoma refers to cancer made up of malignant epithelial cells (eg basal cell carcinoma, illustrated).
Basal cell carcinoma
Catagen
Catagen is a short involutional phase of the hair cycle.
Hair cycle
Cephalic
Cephalic location means on or near to the head.
Chromonychia
Chromonychia is discolouration of the nail.
Cicatricial
Cicatricial is a term used for scarring (cicatrix, a scar).
Circumscribed
Circumscribed means well defined or that a lesion has a distinct edge.
Coalescing
Coalescing refers to two or more lesions merging into one.
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.
Comedo
Comedo has the plural "comedones", and is a plugged hair follicle, ie a blackhead or a whitehead.
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.
Confluent
Confluent refers to two or more lesions merging into one.
Connective tissue
Connective tissue of the skin refers to dermis and subcutaneous tissue.
Skin structure
Cornoid
Cornoid means like a horn.
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
Cryoglobulin
A cryoglobulin is an antibody that precipitates out the blood in the cold.
Cutaneous
Cutaneous means of the skin or relating to the skin.
Cutis
Cutis is a classical term for the skin.
Cyst
A cyst is a papule or nodule that contains fluid or semi-fluid material so is fluctuant.
Cyst
Darier sign
A positive Darier sign in mastocystosis is wealing following stroking the skin.
Dendritic cells
Dendritic cells are cells with long finger-like processes (dendrites), and include melanocytes, Langerhans cells and some tissue macrophages (immune cells).
Dermal
Dermal means of the skin or belonging to the skin, or may specifically refer to the dermis.
Dermatologist
A dermatologist is the medical or surgical specialist in diseases of skin, hair and nails. Refer to DermNet's pages, What is a Dermatologist.
Dermatology
Dermatology is the study of skin, hair and nails.
Dermatitis
Dermatitis has several meanings, including inflammation of the skin. It is often used in the context of a kind of eczema.
Dermatomal
Dermatomal is corresponding with nerve root distribution (dermatome), as seen with the blistering rash, herpes zoster (shingles, illustrated).
Herpes zoster
Dermatopathologist
A dermatopathologist is medical specialist in the pathology of skin diseases. Dermatopathologists may also be general pathologists or dermatologists.
Dermatopathology
Dermatopathology is the study of the microscopic appearance of skin diseases.
Dermatoscopy or dermoscopy
Dermatoscopy refers to the use of a special magnifying device (a dermatoscope) to examine the skin, hair and nails.
Dermatosis
Dermatosis is another name for skin disease.
Dermatosis
Dermis
The dermis is the middle connective tissue layer of skin, (mesoderm) underneath the dermis and above the subcutaneous layer. It is 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
Diascopy
Diascopy is a test using pressure from clear glass or plastic to see if a rash blanches or not.
Discoid
Discoid shape is round, like a disk.
Discrete
A discrete lesion is separated from other lesions by normal skin.
Disseminated
Disseminated means widespread. Lesions are scattered all over a region or all over the body.
Distal
Distal location means located away from the centre of the body.
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.
Dorsal
Dorsal location means on the upper surface or back of a body part (posterior).
Dyskeratosis
Acantholysis is a histological term referring to abnormal keratinocytes.
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.
Elastosis
Elastosis is a histological term referring to changes within the elastic tissue of the dermis.
Electrophoresis
Electrophoresis is a laboratory technique used to separate proteins by their size. The technique applies a negative charge so proteins move towards a positive charge.
Embolus
Embolus is a small particle (eg blood clot, clump of bacteria, air bubble) that has been carried through the bloodstream and block a small blood vessel. Plural is emboli.
Eosinophilia
Eosinophilia refers to many eosinophils in the blood.
Eosinophils
Eosinophils are inflammatory cells, named by their tendency to stain red with eosin. They are characteristic of some kinds of eczema and other inflammatory diseases, drug eruptions and parasitic infections.
Epidermis
The epidermis is the outer epithelial layer of the skin, and is mainly composed of keratinocytes. It overlies the dermis.
Epidermis
Epidermotropism
Epidermotropism is a histological term referring to the tendency for inflammatory cells to move towards and into the 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
Eponychium
Eponychium is the nail cuticle, the skin between the proximal nail fold and the nail plate.
Erosion
Erosion is caused by loss of the surface (epidermis) of a skin lesion; it is a shallow moist or crusted lesion.
Erosions
Erythema, erythematous
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
Eschar is dark-coloured adherent crust of dead tissue found on some ulcers.
Exanthem
An exanthem is a widespread rash that is usually accompanied by systemic symptoms such as fever, malaise and headache. It is caused by infection or drug.
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
Exocytosis
Exocytosis is a histological term referring to random passage of inflammatory cells into the epidermis.
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
Exostosis
Exostosis is a growth coming out of bone.
Exudate
Exudate is ooze from an erosion or ruptured blister.
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).
Fibrosis
The process by which the body lays down collagen or fibrous tissue.
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 means pertaining to hair follicles.
Folliculitis
Fungating
Fungating refers to a large malignant tumour that is erupting like a mushroom or fungus.
Fungating lesion
Furfuraceous
Furfuraceous is a description of scale in which is bran-like or powdery.
Furfuraceous scale
Glabrous
Glabrous skin has a smooth surface and is hairless, ie, palms, soles, lips, eyelids and genital skin.
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 referring to chronic inflammation in which there are several types of inflammatory cells including giant cells.
Granuloma annulare
Grenz zone
Grenz zone is a histological term referring to an area of uninvolved skin underneath the epidermis.
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).
Grouped
A cluster of lesions is sometimes described as grouped.
Gyrate rash
A gyrate rash appears to be whirling in a circle.
Gyrate rash
Haematoma
A haematoma is a swelling due a collection of blood.
Haemosiderin
Haemosiderin is a brown pigment containing iron and is derived from blood.
Haemorrhage
A haemorrhage is a bleed.
Haemorrhagic
Haemorrhagic refers to blood, eg haemorrhagic bulla is a blood-filled blister.
Hair
Hair is a specialised epidermal product of the pilosebaceous structure, and is made of keratin. 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
Hamartoma
A hamartoma is a benign malformation within the tissue of origin. It grows at the same rate as the surrounding tissues. It is composed of a disorganised mass of tissue elements normally found at that site. In the skin, it presents as a birthmark.
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
Histology
Histology is the study of the microscopic appearance of biological tissues.
Histopathology
Histopathology is the study of the microscopic appearance of diseasesd biological tissues.
Horn
An accumulation of hard keratin layer on the skin surface is called a cutaneous horn.
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
Hyalinisation
Hyalinisation is a histological term referring to a ground-glass appearance of the dermis.
Hypergranulosis
Hypergranulosis is a histological term referring to an increased numbers of granules within the granular layer of the epidermis compared to normal.
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
Hypertrophy explains that some component of the skin such as a scar is enlarged or has grown excessively.
Keloid
Hyponychium
Hyponychium is the skin under the distal end of the nail plate.
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.
Immunofluorescence
Immunofluorescence refers to laboratory tests that reveal immune cells by tagging them with a fluorescent marker.
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.
Infection
Infection is illness caused by pathogenic organism (viruses, bacteria, fungi, parasites).
Inferior
Inferior location means on the lower surface of a body part or closer to the feet.
Infestation
Infestation is illness caused by parasitic invasion, eg scabies mite, human fleas.
Inflammation
Inflammation in the skin is its response to injury or disease. It is recognised by redness, often accompanied by swelling, heat and pain and/or itch.
Integument
The integument is an enveloping layer, ie the skin and outer mucosal surfaces of a human.
Interface dermatitis
Interface dermatitis is a histological term referring to mild lichenoid-like reaction in the interface between epidermis and dermis.
Intertrigo
Intertrigo is a rash affecting body folds.
Iris lesion
An iris lesion refers to concentric red rings. Also called target lesion or bull's eye appearance.
Isomorphic phenomenon
The isomorphic or Koebner phenomenon refers to the tendency of several skin conditions to affect areas subjected to injury.
Psoriasis
Keratin
Keratin is the protein produced by keratinocytes, forming the bulk of epidermis, hair and nails.
Fingernail
Keratinisation
Keratinisation is the process by which skin cells mature and produce the protein keratin.
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
Koilocyte
A koilocyte is a pale cell with a dark nucleus as observed on histology.
Koilonychia
Koilonychia is a concave or spoon-shaped nail.
Koilonychia
Lamella
Lamella is a layer.
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
Lateral
Lateral location means on or towards the side of a body part.
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
Leukonychia
Leukonychia means completely or partially white nail.
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
Lunula
Lunula is moon or crescent-shaped whitish area at the base of a nail and is the visible part of the nail matrix.
Lymphocytes
Lymphocytes are important cells in acquired immune defence. B cells produce antibodies. T cells bind antigens. They are often found in biopsies of chronic inflammatory skin diseases.
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
Madarosis
Madarosis (baldness) usually refers to loss of eyelashes.
Malignant
The term malignant is usually used in reference to a cancer. Malignant means the lesion or disease has a poor prognosis if left untreated.
Matrix of nail
The nail matrix is the tissue from which the nail is formed. The ventral nail plate is formed from the nail bed and dorsal nail plate is formed from the proximal nail matrix under the nail fold.
Medial
Medial means on or towards the middle of the trunk (the median axis of the body).
Median canaliform dystrophy
Median canaliform dystrophy results in a longitudinal groove in a nail plate.
Nail groove due to myxoid cyst
Melanin
Melanin is the brown coloured protein made by melanocytes.
Melanoma
Melanocytes
Melanocytes are pigment cells 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, which can arise from the epidermis, the dermis or both. Cancerous melanocytic tumours are called malignant melanoma.
Epidermis
Melanonychia
Melanonychia is a band of brown or black discolouration on a nail plate.
Melanonychia
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.
Metastasis/es
Metastasis means spread of disease to another part of the body. It is usually used in the context of a cancer, when it may also be called a secondary tumour.
Morbidity
Morbidity is the state of being unwell.
Morphology
Morphology is the form or structure of an individual skin lesion.
Mucous
Mucous is the adjective belonging to mucus, as in mucous membrane.
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
Mucus
Mucus is secretion from mucous membrane, eg nasal mucus.
Myxoid
Myxoid means derived from mucus or other secretion.
Mucosa
Myxomatous
Myxomatous is a histological term referring to deposition of extra ground substance within the dermis.
Nails
The nail plate is composed of horny cells containing keratin and is produced by nail matrix. Healthy fingernails grow 0.1 mm per day; toenails grow 0.03 mm per day.
Normal nail
Necrobiosis
Necrobiosis is a histological term referring to accumulation of mucopolyusaccharides in dermal collagen that alters its appearance.
Neoplasm
Neoplasm is an abnormal proliferation of cells; it can be benign (harmless) or malignant (cancer).
Neutrophils
Neutrophils are inflammatory cells that act quickly to help heal an injury or clear infection.
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
NSAID
NSAID is an acronym for nonsteroidal anti-inflammatory drugs.
Nummular lesion
Round (coin-shaped) lesions. Also known as discoid.
Nummular lesion
Oedema
Oedema (American spelling ‘edema’) refers to tissue swelling.
Oedema
Oil drop
An oil drop is an orange or brown streak on a nail plate, found proximal to onycholysis
Psoriatic nail dystrophy
Onychauxis
Onychauxis is a thick nail plate.
Longitudinal nail ridging
Onychia
Onychia is inflammation of the nail matrix.
Onychocryptosis
Onychocryptosis is an in-growing nail.
Ingrowing nail
Onychogryphosis
Onychogryphosis is a thick hard curved nail plate in the shape of a ram's horn.
Longitudinal nail ridging
Onycholysis
Onycholysis is a whhite or yellow apparing part of a nail plate, where it has lifted off the nail bed.
Onycholysis
Onychomadesis
Onychomadesis means loss of nail.
Nail shedding due to lichen planus
Onychorrhexis
Onychorrhexis is longitudinal ridging affecting a nail plate.
Onychogryphosis
Onychoschizia
Onychoschizia is distal lamellar splitting/brittle nails due to water/detergent damage
Nail splitting: onychoschizia
Orthokeratosis
Orthokeratosis is normal stratum corneum, ie surface keratinised cells of the skin that do not contain nuclei.
Pachyonychia
Pachyonychia is a wedge-shaped nail.
Pachyonychia
Panniculitis
Panniculitis is inflammation of the pannus, or subcutaneous fat.
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
Papillomatosis
Papillomatosis is a histological term referring to an undulating appearance of the epidermis.
Papillomatous
A papillomatous lesion has a bumpy and elevated surface.
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
Parakeratosis
Parkaeratosis is abnormal stratum corneum, in which surface keratinised cells of the skin retain nuclei.
Paraneoplastic
A paraneoplastic sign indicates the presence of an internal cancer.
Paronychia
Paronychia means around the nail, and usually implies an inflammatory process.
Acute herpetic paronychia
Pathogen
A pathogen is a specific infective organism (type of bacteria, fungus, virus, or parasite).
Pathology
Pathology is the study of the causes of disease, often used to describe medical science undertaken in a laboratory.
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
Perivascular
Perivascular is a histological term meaning around blood vessels.
Petechiae
Petechiae are pinpoint < 3 mm, red, purple or brown spots — a form of purpura.
Petechiae
Petechial haemorrhages
Petechial haemorrhages are pinpoint < 3 mm, red, purple or brown spots — a form of purpura.
Petechiae
Pigment
Pigment is colour, as in colour of the skin.
Pilosebaceous structures
The pilosebaceous structures contain hair and sebaceous glands (oil glands).
Skin structure
Pitting
Pitting refers to tiny depressions in a nail plate.
Nail psoriasis pitting
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 and pigmentation.
Poikiloderma
Polygonal
A polygonal skin lesion means it has a non-geometric shape.
Erythema
Polymorphic
A polymorphic or polymorphous eruption means the lesions may have varied shapes.
Lichen planus
Posterior
Posterior location means behind, or on the back of a body part (dorsal).
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
Prognosis
The prognosis means the likely course of a condition.
Proximal
Proximal site means located close to the centre of the body.
Pruritic
Pruritic is a descriptive term meaning itchy.
Pruritus
Pruritus means itch.
Pseudocyst
Pseudocyst differs from true cyst because it lacks a capsule.
Pseudoepitheliomatous
Pseudoepitheliomatous is a histological term referring to harmless thickening of all layers of the epidermis that resembles squamous cell carcinoma.
Psoriasiform
Psoriasiform means resembles psoriasis.
Pterygium
A pterygium is a wing of extra tissue.
Pterygium of nail due to lichen planus
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
Pyknosis-
Pyknosis refers to a darkly-staining, small, dying cell on histology.
Pyo-
Pyo- refers to pus.
Pyogenic
Pyogenic means producing pus.
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
Scale, scaling, scaly
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
Scar
A scar is a healed lesion following injury to the dermis or subcutaneous tissue, leading to new collagen formation. Usually permanent.
Sclerosis
Sclerosis is 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 and 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
Sinus
A sinus is a tunnel or cavity leading to skin surface, eg from an abscess.
Slough
Slough is the surface material on an ulcer, made up of exudate and necrotic tissue.
Spongiosis
Spongiosis is a histological term referring to intercellular swelling of the epidermis, which resembles a sponge.
Squamous
Squamous is a histological term referring to the cells that produce scale.
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
Stomatitis
Stomatitis is a general term for inflammation of the mucous membrane of the mouth.
Stratum corneum
The stratum corneum is the surface horny layer consisting of stacks of dead cells without nuclei.
Epidermis
Stratum granulosum
The stratum granulosum is the layer of the epidermis under the stratum corneum, and is characterised by flattened cells filled with dark granules containing keratohyaline protein.
Epidermis
Stratum spinosum
The stratum spinosum or prickle cell layer of the epidermis 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. It is also called subcutis.
Skin structure
Superior
Superior location means on the upper surface of a body part or closer to the head.
Subungal
Subungual means underneath the nail plate.
Symmetrical
Symmetrical means both sides are the same or similar.
Target lesion
A target lesion has concentric rings like a dartboard. Also known as bull's eye or 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
Thromboembolism
Thromboembolism refers to a blood clot that has broken off and is carried in the blood stream to occlude a smaller blood vessel.
Thrombus
Thrombus is a blood clot that has formed within a blood vessel. Plural is thrombi.
Toxic erythema
Toxic erythema is an acute rash with fever, caused by infection or drug.
Trachyonychia
Trachyonychia means rough nails.
Twenty nail dystrophy trachyonychia
Transepidermal
Transepidermal means across the epidermis.
Transudate
A transudate refers to a watery fluid extruded from tissue, eg saliva.
Tumour
A tumour is a benign or malignant growth of tissue.
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
Unilateral
A unilateral condition affects one side only.
Urticarial
An urticarial condition is characterised by wheals, like urticaria.
Vacuolar
Vacuolar is a histological term referring to the presence within a cell of empty-appearing, membrane-bound cavities.
Vacuole
Vacuole is a histological term referring to an empty-appearing, membrane-bound component of a cell.
Vasculitis
Inflamed blood vessels.
Ventral
Ventral location means on the lower surface or front of a body part (anterior).
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
Warty
A warty lesion is elevated with hard bumps on the skin surface.
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
Well-defined
A well-defined lesion has a clear border separating it from surrounding skin.
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


DermNet NZ does not provide an online consultation service.
If you have any concerns with your skin or its treatment, see a dermatologist for advice.