2.1.3.2　Generation and regulation of pigment

Skin pigmentation is mainly due to the accumulation of melanin granules in keratinocytes.Melanocytes secrete melanin into the melanosome，which then moves into the keratinocyte and reassembles in the supranuclear area to form a melanin cap，protecting the keratinocyte nucleus from ultraviolet damage.

Skin pigmentation is a delicate and complex process，which includes many regulatory mechanisms in intracellular signalling pathways，non-coding RNAs（miRNAs and lncRNAs）and circulating exosomes.Skin pigmentation is regulated by the secretion of cytokines（such as α-MSH，SCF，KGF and bFGF）through the interaction of melanocytes and keratinocytes in the epidermis and fibroblasts in the dermis.(https://www.daowen.com)