Dandruff (squama; skin scales; ICD-10 R23.4: changes in skin relief) occurs when cells of the uppermost skin layer, the keratinocytes (horny cells), die and consequently separate from the other skin layers. This is a physiological (natural, normal) process and serves to regenerate the skin.
Normally, these skin scales are not visible. Only from an aggregation (clustering of individual cells into associations) of 500 and more cells do the skin scales become visible to the human eye. The cause lies in a disturbance of the coordination of the exfoliation, as it occurs in the context of different diseases of the skin (e.g. psoriasis or seborrheic dermatitis).
A plaque (French: plaque; German: Platte) is a “plate-like” proliferation of skin substance that rises above the level of the skin.
A plaque develops from papules that have moved together and fused to form a (plate-like) plateau or from a centrifugally growing papule (nodule-like change on skin or mucous membrane).
Substantial proliferation of the skin manifests as a solid elevation of the skin:
- Plaque: planar increase > 1.0 cm in diameter.
- Papules: circumscribed skin elevation < 1.0 cm in diameter
- Nodus (node): circumscribed in or above the skin protruding tissue consolidation > 1.0 cm
Typical examples of plaque occurrence include psoriasis plaque, senile wart (synonyms: seborrheic keratosis; verruca seborrhoica; seborrheic wart), and cutaneous T-cell lymphoma.
Scales and plaques can be a symptom of many diseases (see under “Differential Diagnoses”).
Course and prognosis: In most cases, the noticeable scaling of the skin is harmless and transient. If additional signs of inflammation of the skin such as rubor (redness), tumor (swelling), calor (hyperthermia), or dolor (pain) occur, these indicate an underlying disease.
