Melanogenesis is the biological mechanism that the body has to defend itself from the potential damage that solar radiation can cause to the cell's DNA. It consists in the production of melanin by the melanocyte, which is the innermost layer of the epidermis, and its subsequent transfer to the epidermis' keratinocytes, which are cells subject to greater exposure to solar radiation due to their superficial location. This is a complex mechanism, in which several exogenous and endogenous factors intervene (physical, biochemical and morphological factors of the skin), and the ultimate objective of which is to create a UV protective barrier in the cell nucleus.
Melanin is produced in the melanosomes (the vesicles that are transferred from the melanocyte to the keratinocyte) from the amino acid tyrosine. The enzyme tyrosinase catalyses a sequential oxidation process by means of which tyrosine transforms into the intermediate DOPA, which in turn is transformed into dopaquinone.
Sometimes, an excess of melanin can be produced due to external factors (solar radiation, certain medications, exposure to some chemicals, etc.) and internal factors (hormone levels, genetic predisposition, ageing, inflammatory processes, etc.) that give rise to different clinical manifestations:
• Melasma is the most severe and resistant hyperpigmentation, and it is mainly associated with hormonal factors. It can appear following pregnancy or hormone treatments, such as contraceptives or hormone replacement therapy.
• Solar and senile lentigo is the hyperpigmentation associated with photoageing. They increase with age and usually appear in areas of the skin exposed to the sun, such as the face, neck and hands.
• Post-inflammatory hyperpigmentation (PIH) are injuries caused by inflammation, such as scarring, acne marks, or after applying certain therapeutic procedures.
• Ephelides or freckles are small brown hyperpigmentations that appear on the skin exposed to the sun, which darkens it. They have a genetic component and mainly affect people with clear phototype.