Melanins are a diverse group of pigments that give rise to color in our skin, hair, and eyes. While melanins serve multiple functions in our bodies, arguably the most important one is protecting our skin from the harmful effects of sunlight.1
Two basic classes of melanins
There are two basic classes of melanins – eumelanins, that are the dominant type found in skin and are black/brown pigments, and pheomelanins are yellow/red/brown.1 All melanins are produced by melanocytes, which are a rare cell type in our outermost layer of skin, called the epidermis. Specifically, melanocytes are located at the bottom of the epidermis and they generate melanin inside membrane-bound structures called melanosomes. Melanocytes transfer melanosomes to the cells above, called keratinocytes, and keratinocytes are the dominant cell type in our outermost layer of skin.
You’ve probably heard of UVA and UVB rays, but here’s a quick reminder of how they are different. UVA rays are the longer wavelength rays and represent the majority of UV radiation that reaches the atmosphere. UVB rays are shorter wavelength and comprise only a minority of UV radiation. As the ozone layer is increasingly depleted, we experience more UVB rays, which is concerning given that UVB rays are the rays that are the most damaging and mutagenic (capable of causing mutations). UVA rays are also damaging to our genetic material, and you experience UVA rays even while sitting in the shade.2 UVA rays penetrate deeper into our skin than UVB rays do, and can have mutagenic effects in the dermis, the second layer of our skin that is located below the epidermis.
Both UVA and UVB rays can cause genetic mutations in our DNA. Fortunately, we have proteins to detect and repair DNA mutations. If a mutation fails to be detected and repaired, the mutation multiplies when the cell divides. And if that mutation is located within certain genes, it may lead to cancer.
In BCC, the most common skin cancer, and in SCC, the second most common skin cancer, mutations associated with UVB damage are found in over 50% of patients.2-4
How does melanin protect us from UV rays?
Melanin protects our skin from light in several ways. It absorbs and re-distributes the light energy from UV rays, and it shields our genetic material stored in nuclei from the rays.
How are race, melanin, and skin cancer connected?
White skinned people are about 70 times more likely to develop skin cancer than individuals with black skin, which suggests that pigmentation is a key risk factor in skin cancer.1 The difference lies not in the number of melanin-producing melanocytes, but in the amount of melanin produced. Asian individuals have, on average, two-fold more melanin than Caucasian people, while Africans have around three to six-fold more melanin. Since the frequency of skin cancer in white and black skinned people differs by a factor of 70, clearly other factors besides melanin quantity are contributing factors.
Another contributing factor may have to do with the longevity of the melanosomes. A study found that melanosomes in dark-skinned people are more resistant to cellular degradation (when cells become too unstable in an organism, resulting in its ultimate death) than they are in white-skinned individuals.2
Melanin, like sunscreen, has an SPF or sun protective factor. Scientists debate exactly how much SPF melanin has, but it’s around SPF 1.5 – 2 and could be as high as 4. That might not sound like very much, but an SPF 2 represents doubling the amount of protection from the sun. If you think of this another way, melanin absorbs or re-distributes around half of the UV light we’re exposed to.
You may wonder whether different ratios of eumelanin to pheomelanin exist in different races. Eumelanin is the type of melanin that dark-skinned individuals have more of, while no differences have been detected for pheomelanin (all races have it). Intriguingly, melanosomes are physically longer in black-skinned individuals than they are in white-skinned ones. Scientists are currently interested in the idea that black skin is more protected from the harmful effects of light in part because melanin is better distributed in these elongated melanosomes, while melanosomes in white skinned people are shorter and more clustered.2
How does UV light impact skin pigmentation?
Following DNA damage or repair from UV light exposure, we increase production of melanin and this creates a tanning effect.2 How pigmentation of the skin is regulated is not well understood but will likely be the subject of future investigation. In mammals, it is known that more than 120 genes have a role in pigmentation.2
Is more melanin always better?
There is evidence that in addition to its photoprotective qualities, melanin can also be toxic to cells grown in culture dishes after UV exposure. Specifically, melanin can produce reactive oxygen compounds that can lead to a break in a single strand of DNA, and pheomelanin can generate hydrogen peroxide which may cause mutations. Whether this happens in human skin and whether it impacts cancer is unknown at this time.
What’s on the horizon in melanin research?
In recent years, melanin research has expanded from studies aimed at understanding how melanin protects us from UV light to a variety of applied disciplines including materials science, drug delivery, and electronics.1 This surge of interest in melanin pigments may yield new discoveries that are relevant to understanding the role of melanin in skin cancer.
d’Ischia M, Wakamatsu K, Cicoria F et al. Melanins and melanogenesis: from pigment cells to human health and technological applications. Pigment Cell Melanoma Res, 2015; 28(5): 520-544.
Brenner M, Hearing V. The protective role of melanin against UV damage in human skin. Photochem Photobiol, 2008; 84(3): 539-549.
Skincancer.org. Available at: https://www.skincancer.org/skin-cancer-information/squamous-cell-carcinoma. Accessed July 29, 2018.
Skincancer.org. Available at: https://www.skincancer.org/skin-cancer-information/basal-cell-carcinoma. Accessed July 29, 2018.