Pigmentation

Author: Prof. Dr. med. Peter Altmeyer

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Last updated on: 29.10.2020

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Definition
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In a broader sense, skin/mucosa pigmentation refers to the storage of pigments (pigmentum = colour, dye) in the skin, skin appendages (hair, nails), eyes and mucous membrane. In humans, the most important pigments are melanin, oxidised haemoglobin and its derivatives haemosiderin, carotenoids and bile dyes. Their composition and density define the skin colour.

In a narrower sense, pigmentation is understood to be melanotic pigmentation (see also Pigment), i.e. the incorporation of the " melanocyte product" melanin into human cells.

Classification
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A distinction must be made:
  • immediate pigmentation (pigmentation immediately after irradiation in the UVA range).
  • Late pigmentation (skin tanning 24-72 hours after exposure to sunlight or UVB radiation; persists for weeks to months).

General information
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Melanin pigments primarily protect the skin against UV radiation. Classification. The genome of an individual has a significant influence on the pigmentation of the skin. This is the reason for the different skin colouring in different ethnic groups. Apparently, various photo products originating from the amino acid troptophane via the aryl hydrocarbon receptor (AhR) play a major role in UV-induced pigmentation. AhR is formed by all cells of the epidermis (keratinocytes, Langerhans cells, melanocytes) and can activate a number of genes (CYP450; COX-2 - see below cyclooxygenase-2). In the skin, AhR acts as a sensor for UV rays, among other things.

Etiology
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More than 150 genes are involved in the melanocytic (melanocytic) pigment formation. Gene defects can cause disturbances at any point of the cascade. Pigmentation disorders are caused by:
  • Change in melanocyte count
  • inadequate melanin synthesis
  • defects in the maturation, transport or transfer of melanosomes
Increased skin tanning is the physiological response of the pigment system to UV radiation. Pigmentation protects against a number of UV-induced biological effects, particularly photocarcinogenesis.

Note(s)
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A linguistic distinction is made between physiological pigmentation (normal skin tanning) and pathological pigmentation(hyperpigmentation), which can be caused by numerous influences (physical, inflammatory, hormonal, chemical). The opposite of a hyperpigmentation is a (pathological) depigmentation.

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Last updated on: 29.10.2020