Abstract
Melanocytes are highly specialised dendritic cells that transfer melanin to keratinocytes in subcellular lysosome-like organelles called melanosomes, where melanin is synthesised and stored. Melanin is a complex pigment that provides colour and photoprotection to the skin, hair, and eyes of mammals. The regulation of melanogenesis includes various mechanisms and factors including genetic, environmental, and endocrine factors. Knowledge of the pigmentation process is important not only to understand hyperpigmentation but also to design treatments and therapies to treat them. Whitening cosmetics with anti-melanogenesis activity are very popular. In the present manuscript, we review the mechanisms and the signalling pathways involved in skin pigmentation and we specifically focus on the alteration of melanogenesis that leads to melasma and results in hyperpigmentation. Finally, current therapies and treatments including topical, oral, and phototherapies are discussed and described, with a special emphasis on the cosmetics’ action.
Highlights
Melanin is a complex pigment that provides colour and photoprotection to the skin, hair, and eyes of mammals
Stem cell factor (SCF), a paracrine factor located in fibroblasts, binds to its tyrosine kinase receptor c-KIT, which is produced by melanocytes, leads to the activation of the Ras-MAP
microphthalmia-associated transcription factor (MITF) regulation is the key factor in melanogenesis and is the main target for the induction of pigmentation in melasma
Summary
Melanin is a complex pigment that provides colour and photoprotection to the skin, hair, and eyes of mammals. Melanogenesis, the process through which melanocytes synthesise melanin, can be altered, producing pigmentary skin disorders such as melasma which result in hyperpigmentation. Melanocytes are highly specialised dendritic cells that transfer melanin to keratinocytes in subcellular lysosome-like organelles called melanosomes, where melanin is synthesised and stored. Fitzpatrick and Breathnach proposed in 1963 the “epidermal melanin unit”. This concept consisted of the interaction of 1 melanocyte and approximately 36 keratinocytes to produce pigmentation. Langerhans–melanocyte (KLM) unit has been proposed, which does not exclude the possibility of including other epidermal cells [1]. Knowledge of the pigmentation process is important for designing bleaching products to treat skin hyperpigmentation
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