Figure 2: Melanin Biosynthesis. Melanins are large bioaggregates composed of pigmented precursors originally derived from the amino acid tyrosine. Epidermal melanins are present in two major forms: (1) eumelanin, an effective UV-blocking brown/black pigment and (2) pheomelanin, a sulfur-containing red/blonde pigment less able to absorb UV photons. The melanocyte stimulating hormone (MSH) - melanocortin 1 receptor (Mc1r) signaling axis is a major determinant of the type and amount of melanin produced by melanocytes in the skin.