What is the Biology of Skin Color?

Does President Barack Obama have a different number of melanocytes than his predecessors? Nope!

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?

MELANOCYTE COUNT

The tyrosinase enzyme. A mutation of the corresponding gene is what’s responsible for albinism, not a lack of melanocytes!

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 are distributed throughout the epidermis (the dark berry areas). In white skin, they are limited primarily to the second to last layer in the picture: the basal layer.

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.

BOTTOM LINE

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!

by Nicki Zevola

5 thoughts on “What is the Biology of Skin Color?

  1. janine says:

    As ordinary and overdone as it might sound, I would relish a post dedicated to the topic of exfoliation. What are the best vehicles and why? What ingredients, substance and tools to avoid? Frequency required for efficacy? Can one safely exfoliate the decollate? And I would love to know if the Clarisonic is really an “exfoliator” or just an effective cleaning tool…….
    The word exfoliation has been crammed down the throats of all us forty-something year olds and I demand clarity!
    Just sayin’……….

  2. John Su says:

    @janine

    It’s not ordinary at all because the science behind exfoliation is complicated! I’m not sure if you saw my 4-part series on hydroxy acids, but that might give you an idea of how confusing exfoliation can be.

    I already have an exfoliation series on my “to-do” list haha! It’s going to be either 4-5 parts. I just don’t plan to do it too soon since I just finished the 5-part sunscreen series. I just don’t want people to be overwhelmed, so I plan to do some shorter singlular posts for now.

    To give you an idea of what’s in the works, I also have a 3-5 series planned on what exactly occurs in when our favorite ingredients “oxidize” either by air of sun exposure, etc… Another series on natural vs synthetic or in other words, distilled vs wholly ingredients…. Another series on microemulsions, DIY treatments, etc… it kind of goes on and on. :) So yeah. I’m just trying to find interesting posts to fill in the gaps between these larger series.

    In the meantime, if you haven’t already, check out the hydroxy acids series that I wrote a few months ago!

    Thanks for the suggestion!

    And yes, the Clarisonic is an exfoliator, albeit a physical or manual one. An exfoliator is anything that takes away a meaningful amount of the dead skin cells or non-nucleated corneocytes of the stratum corneum.

  3. janine says:

    wow- a 4 part series on hydroxy acids! I’ll be all over that. Under what rock (link) has this little gem been hiding?
    I eagerly await all those pending multi-part posts.
    As always: thank you.

  4. Pingback: Why Does It Take So Long to Treat Hyperpigmentation? | FutureDerm - Skin Care - Retinol - Beauty Blog

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