How the tan is made
The tan MT-II produces is not a stain or a dye.
From receptor to pigment: how MT-II darkens skin
The tan MT-II produces is not a stain or a dye. It is the end of a real biological cascade: MT-II switches on MC1R, and in the relay described for the natural hormone, a messenger surge activates a master pigment gene that ramps up the enzymes that build melanin inside skin cells.
This unit follows that chain link by link, explains the crucial difference between protective and damaging melanin, and confronts the most dangerous myth around MT-II: that a chemical tan protects you from the sun.
Key terms
The melanin cascade
MC1R on a melanocyte sits at the top of a defined relay that ends in pigment. The relay below is the one described for the natural hormone alpha-MSH, and MT-II is a cyclic analogue of that hormone, so this is the route it is understood to take. Be clear about the limit: none of the MT-II study abstracts in this course reports a messenger, a gene or an enzyme measured after a dose; the human pilot measured skin colour. This is the best-characterised biology in the course and it is still borrowed from the natural ligand.
Follow the logic and the tan demystifies itself. The receptor surge does not "make pigment" directly; it flips a master gene (MITF), which switches on the enzyme genes, and tyrosinase then builds melanin from a common amino acid. The pigment is handed from melanocytes to surrounding keratinocytes inside melanosomes, carried along the melanocyte dendrites, where it builds up as visible darkening; the pilot measured it a week after dosing ended.
AdvancedWhy the tan appears gradually and outlasts the dose
Because the effect runs through gene transcription and enzyme synthesis, it cannot be instant. New enzyme has to be made, melanin has to accumulate, and pigment has to transfer to keratinocytes. That fits the original trial, where visible tanning followed about five doses over two weeks, and it fits colour outlasting dosing: the pilot measured increased pigmentation by reflectance and by eye one week after dosing ended. How much longer than that it lasts, the pilot's abstract does not say.