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23

The blue colour is an example of structural colour, caused by light interacting physically with something. Some examples of structural colour are the iridescence of insect wings and body surfaces (usually caused by repeating chitinous structures), and of certain birds feathers, as well as the non-iridescent colours of the blue and yellow macaw. In the case ...


17

The generation of iris color is quite complex and the exact color of the eyes depends upon many different factors, not just melanin. In fact, blue coloration does not depend on a specific chemical, but on the structure of the eye itself. This very nice review (free) summarizes our current understanding: Genetics of human iris colour and patterns - Sturm and ...


6

Surprisingly, it is indeed possible! But, the fact is that the actual process is a bit more complex and might actually require more compounds along with cysteine to give such effects in living beings. First of all, see this image1: As is clear from the diagram, GSH (glutathione) is also a factor for pheomelanin production, along with cysteine. Another ...


3

The answer to this question has its reason in the hair cycle. Our hair goes through a cycle of growth. At the end of this cycle, the cells in the hair follicle die and have to be replenished before a new hair cycle starts, also the hair falls out eventually. See the figure from reference 1: The replenishment process is done by to two cell types: Epithelial ...


3

Let's have a look at the pathway first (this figure is figure 2 from reference 1), which shows the basic pathway of pigment biosynthesis: The first important step, the oxidation of the amino acid tyrosine to Dopaquinone (DOPA) by the tyrosinase is the same for both pathways (eumelanin and pheomelanin production) and rate limiting. The important step is ...


3

Since Eumelanin is the protective form of melanin and there is some research available that Pheomelanin contributes to the generation of reactive oxygen species which are harmful to the cell (see reference 1, which contains a lot of further references on this topic), I don't see any reason to do so, but ok. Additionally removing Eumelanin from your skin will ...


2

The upper layer of the skin (or the epidermis) is formed mostly by keratinocytes and some melanocytes (about 30-40 times more keratinocytes) and also fibroblasts (although they are not shown here). The melanocytes are found in the basal cell layer at the border between epidermis and dermis as shown in the figure below (from here): The melanocytes spread out ...


2

The tanning response to UV occurs in two phases: The immediate response begins at exposure to UV-A, reaches a max at 1-2 hours, and fades between 3 and 24 hours. This article speculates that this is due to the redistribution of melanosomes rather than additional melanin production. The delayed response is more durable, occurring by repeated exposure to UV-B,...


1

The absorption of gamma and x-ray radiation by skin is negligible, so the amount of melanin present is irrelevant. Stopping high energy photons requires a lot of mass, not a few microns of melanin.


1

Pheomelanin is associated with paler skin, while eumelanin predomominates in people with darker skin — this is influenced by alleles of the MC1R gene Swope and Abdel-Malek, 2018, NIH article on MC1R.


1

The actual coat color is determined by the ratio of the products of two genes: Tyr and TyrP1. The first oxidizes DHI to Indole-5,6-quinone and forms brown pigment, TyrP1 on the other hand oxidizes DHICA to Indole-5,6-quinone carbolic acid, which forms black pigment. See this pathway diagram (from here): So loss of TyrP1 activity is not harmful to general ...


1

Mammals are born with blue eyes because the melanin level has not yet been established to give brown/yellow. Blue is the absence of melanin, so that eyes reflect outside light which is seen as blue. Melanocyte cells respond to light and will start to make melanin in the first few weeks after birth. Melanocyte cells have a range of activity and will produce ...


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