Factors that Effect Skin Color
The major effector of human skin color (and hair color) is the pigment melanin. Melanin is produced by melanocytes and transferred to keratinocytes. There are several types of melanin, but here are the major three types. The type of melanin people make along with the amount they make gives them a base skin color.
- Black eumelanin — has a darker color. People with very dark skin produce this type of melanin in larger quantities. Very protective against UV radiation.
- Brown eumelanin — a bit lighter in color than black eumelanin. Good protection against UV radiation.
- Phoemelanin — this melanin gives us red hair and very light skin. Does not protect from UV radiation, in fact it appears to increase the effects of UV radiation.
Melanocytes are the cells that make melanin, and we all basically have the same number of melanocytes. The differences in base skin color that we see are mostly due to different types of melanin, how much melanin is produced, and how fast the melanin is broken down. In many of us some melanocytes are more active than others… this is the source of freckles. Exposure to UV radiation also makes melanocytes more active, that is why tanning works.
Albinism is caused by a lack of melanin production.
So, why do humans have so many different shades of skin color? It has to do with our need for UV radiation to make vitamin D verses the damage that UV radiation can do to our skin. If your ancestors lived in an area near the equator where UV exposure is the greatest then they had more than enough UV radiation for vitamin D production and would need darker pigmentation to protect their skin from excess UV radiation. If your ancestors lived in an area further away from the equator with less UV exposure then darker pigmentation would have been lost in order make enough vitamin D with little UV radiation. Because there is a gradient of UV radiation hitting our planet’s surface as we move from the equator towards the poles there is also a gradient of human skin color. That variation also increases as peoples of different skin colors meet, mingle, and reproduce together.
When we study skin color and melanin ideas of human “races” often come up. Here is a short blog about human “races” from a scientific and anthropological perspective. Race is a cultural construct
Comparing the effects of UV radiation on different skin colors:
(images from Pixabay.com)
The young girl pictured above has darkly pigmented skin probably due to lots of black eumelanin pigments. This puts her at low risk for sunburn, skin cancer, and other damage that UV radiation can do to our skin, including fewer wrinkles and skin sagging as she gets old. The only downside to this pigmentation would be if her family moved to an area with less UV exposure and no vitamin D supplementation, in that case she could have problems with bone development due to lower calcium levels.
The above little girl has pigmentation that is a bit lighter probably due to a lower amount of brown melanin production. She would still be pretty well protected from UV radiation, but a bit more susceptible to sunburn, skin cancer, and skin aging due to UV radiation. If she lived in an area with little UV exposure she would probably need vitamin D supplements.
The lighter skinned girl above would be at low risk for vitamin D deficiency but at much higher risk for sunburn, skin cancer, and sagging/wrinkling skin with aging. Assuming her hair pigmentation is natural she is likely capable of tanning which would give her more protection from UV radiation. However, exposing herself to UV radiation in order to get the tan would cause UV damage to her skin.
The boy above has very pale pheomelanin pigmentation. His pheomelanin pigmentation puts him at even higher risk for UV damage, but if he lived in an area with very little UV radiation exposure he would still be able to make plenty of vitamin D. People with this pigmentation should really avoid UV radiation exposure.
Sunblock pros and cons:
Sunblocks can of course helps decrease the dangers of UV exposure, but they tend to make us think we can stay out in the sun— our time in the sun should still be limited. The lowest risks for skin cancer involve zero exposure to UV radiation. That of course is near impossible, so instead I advocate a thoughtful approach to the risks involved. Above all, make sure that children do not get severe sunburns as this leaves them at very high risk for skin cancer in their later years.
Other factors that effect skin color
- Blood: Skin is a bit see through and we can see the blood inside of a person’s skin as a pinkish or reddish color depending on how dilated the blood vessels under the skin are. Blushing is probably the most obvious example of how blood effects skin color. Cyanosis: Blood becomes a brighter red with more oxygen and darker red when oxygen levels are lower (blood is never blue). This difference in blood color can change our skin color as well. When a person’s blood oxygen level drops their skin can appear a bit blue… often appears in lips and nailbeds first. Cyanosis can also occur when we get cold, due to a decrease in blood flow to the skin.
- Bilirubin: Bilirubin is a pigment produced when red blood cells are broken down (think of the yellowing that occurs during the healing of a bruise). It is the job of the liver to eliminate this pigment and if the liver is not able to eliminate enough bilirubin a person may appear yellowish or jaundiced… this yellow coloration is often most visible in the whites of the eyes. Yellowing of the skin due to bilirubin is called jaundice.
- Carotene pigments: Carotene pigments are made by plants and have an orange or yellow color (carrots are orange due to carotene). It is rare, but it is possible that a person can eat a lot of carotene and cause themselves to have an orange or yellow color. I once knew a body builder who was taking “tanning pills” that contained carotene pigments and it turned his skin orange.