Terminology of Skin Disorders

Terms to describe skin disorders are split into macroscopic and microscopic.

Macroscopic appearances

Macule
A flat, circumscribed lesion; an area of color or textural change. Macules are seen in vitiligo (hypopigmentation), freckles (hyperpigmentation) and capillary haemangioma (red/purple).

Papule
A solid, circumscribed, palpable elevation of skin less than 5 mm in diameter. They can appear in various forms: e.g. dome shaped (xanthomas), flat topped (lichen planus).

Nodule
An elevation more than 5 mm in diameter that may be either solid or edematous. Nodules are seen in rheumatoid arthritis, and a dermatofibroma is another example of this type of lesion.

Plaque
A plaque is an extended, flat-topped lesion, a palpable elevation of skin (measuring no more than 5 mm in elevation but generally more than 2 cm in diameter). Plaques are commonly seen in psoriasis and mycosis fungoides (cutaneous T-cell lymphoma).

Blister
A lesion of any size, filled with clear fluid, that forms because of cleavage of the epidermis. It may be a result of constant abrasion of the skin, or as part of a pathological process. The cleavage may be intraepidermal or at the dermoepidermal junction.

Vesicle
Less than 5 mm in diameter, a vesicle is a skin blister filled with clear fluid. Vesicles may be subepidermal or intraepidermal, and may be single or grouped.

Pustule
Similar to a vesicle, a pustule is filled with a visible collection of yellowish pus. This may indicate infection. A furuncle is an example of an infected pustule; the pustules that appear in psoriasis are sterile.

Bulla
A bulla is a large, fluid-filled blister more than 5 mm in diameter. They occur typically in primary blistering disorders such as bullous pemphigoid, and sometimes in cardiac failure (oedema blisters).

Wheal
Wheals are transitory, itchy, raised, discoloured papules or plaques of oedema. They are usually a sign of urticaria or angio-oedema.

Wheal
Scales are abnormal flat flakes on the skin surface that indicate disordered keratinocyte maturation and keratinization. They vary in appearance, from large white or brown polygonal, like fish scales in ichthyosis, to thick silvery layers in psoriasis.

Lichenification
This is chronic thickening of the epidermis with prominent skin markings, caused by continual rubbing or scratching.

Excoriation
Superficial scratch marks.

Onycholysis
Onycholysis is the separation of the nail plate from the nail bed. Subungual hyperkeratosis subsequently occurs, with the nail plate becoming thickened, crumbly and yellow. It is a feature of many disorders, including psoriasis, fungal infections and trauma.

Petechiae
Petechiae are small, round, flat red spots caused by haemorrhage into the skin or the mucous membranes. They can coalesce to form a purpuric rash.

Purpura
This is a skin rash caused by haemorrhage into the skin from capillaries. It can develop as a result of fragility or damage of the capillaries or an abnormally low blood platelet count.

Microscopic appearances

Hyperkeratosis
This is thickening (hypertrophy) of the surface layer of the epidermis (stratum corneum).

Parakeratosis
Parakeratosis is a pathological process where the nuclei of the cells in the stratum corneum persist. It is seen in disease states such as psoriasis.

Acanthosis
This is thickening (hypertrophy) of the stratum spinosum of the epidermis. It can be regular or irregular.

Dyskeratosis
This term describes a process in which keratinocytes mature early, becoming keratinized before they reach the surface of the skin.

Acantholysis
This is a pathological process where the prickle cells of the stratum spinosum separate, leading to atrophy of the epidermis. Acantholysis is seen in diseases such as pemphigus vulgaris and keratosis follicularis.

Papillomatosis
Accentuated undulating configuration of the demoepidermal junction often seen in psoriasis. Spongiosis This is an inflammatory intercellular oedema of the epidermis.

Erosion
A destructive lesion of the skin that causes a superficial discontinuity confined to the epidermis, and that heals without scarring.

Exocytosis
This term is used in pathology to describe the migration of inflammatory cells into the epidermis.

Ulceration
The formation of a surface defect of the skin (by sloughing of inflammatory, necrotic tissue or trauma).