Pigmentation

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.

• 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).

Melanin pigments primarily serve to protect the skin from UV radiation.

The genome of an individual has a significant influence on the pigmentation of the skin. This is the reason for the different skin colorations in different ethnic groups.

Apparently, various photoproducts derived from the amino acid troptophan play a major role in UV-induced pigmentation via the aryl hydrocarbon receptor (AHR receptor, see AHR gene below). The receptor encoded by the AHR gene is produced 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 functions, among other things, as a sensor for UV rays.

• Change in melanocyte count
• inadequate melanin synthesis
• defects in the maturation, transport or transfer of melanosomes

A linguistic distinction must be 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 hyperpigmentation is (pathological) depigmentation, a pathological loss of pigment.