For the past five weeks, we’ve discussed the efficacy of inorganic and organic sunscreens. Depending on a variety of factors, sunscreens contribute to the color of the skin by preventing or allowing UVB-induced tanning and/or UVA-induced delayed tanning of the skin.
But what determines a person’s skin color in the absence of UV light? In other words, what characterizes a person’s innate skin color?
Surprisingly, all skin colors ranging from fair to deep dark have the same number of melanocytes: approximately 2,000/mm2 on the head and forearm, and 1,000/mm2 on the rest of the body. To further substantiate this fact, it is known that the various types of albinism are caused by defects with the genes that code for the tyrosinase enzyme; the number of melanocytes remains the same.
DISTRIBUTION OF MELANOSOMES
Melanosomes are vesicles that carry melanin, which are made in melanocytes, along dendritic cells to be distributed to the top layer of keratinocytes, where they can better protect the nuclei from further DNA damage. It is in this distribution pathway, where black and white skins differ. The melanosomes in white skin are small and tend to clump together into complexes. The melanosomes in black skin do not aggregate and are much larger in size.
Keep in mind that these two pathways of distribution are not mutually exclusive, as lighter black skin have also been shown to exhibit smaller melanosomes that aggregate into complexes, in addition to singly dispersed ones.
Therefore, it can be said that skin color correlates with melanosomes grouping or clumping. And like with inorganic sunscreen nanoparticles, the innate size of the “particles” or melanosomes in this case, determines its tendency to form aggregates. The larger the size, the less likely it will form aggregates.
LOCATION OF MELANOSOMES
In black skin, melanosomes were shown to be present in not only the basal layer of the epidermis, but also throughout all layers of the epidermis. However, the melanosomes of white skin were limited primarily to the basal layer.
While the facts learned in this post do not really influence how you evaluate skin care, it still contains some valuable and fun (in my opinion) information that may be important in the future. For example, from a clinical point of view, the two most prominent and well-documented melanosomes-transfer inhibitors: niacinamide and soy’s protease inhibitor, can be tested to see how well they perform with lighter and darker skin types, and if there is a difference, why? I have yet to see a study elucidate this mystery, but I’m sure it’d be an interesting read (for me at least)!
I hope you enjoyed this bit of light reading, and if you’d like to nominate a topic for next week’s post, please let me know in the comments section down below!