The Influence of Hormones on Melanogenesis

The contribution of melanin to the colour of the skin is subject to hormonal regulation. Hormones influence the amount and the distribution of melanin in the epidermis. One mechanism by which hormones can influence the amount of melanin involves changes in the activity of the enzyme tyrosinase in the melanoblasts which synthesize the pigment. A second mechanism may involve changes in the activity of keratinocytes which engulf the melanin discharged from melanoblasts. Hormones can also influence the dispersion of melanin. Interstitial cell-stimulating hormone, oestrogens, melanocyte-stimulating hormone and adrenocorticotrophin appear to increase epidermal melanin by enhancing the activity of tyrosinase. Hormones probably exert other effects on epidermal melanin which are less clearly understood. An attempt is made to point out the immediate limitations in our present understanding of the contribution of melanin to the colour of the skin and directions of future investigations are suggested.