Melanins are a group of pigments that give rise to the color in our skin, in our hair and in our eyes. While melanins have several functions in our bodies, probably the most important function is to protect our skin from the harmful effects of sunlight.

There are two basic classes of melanins:

Pheomelanin is a melanin that is found in smaller amounts in skin and hair. Light-skinned people have more pheomelanin than dark-skinned people. Pheomelanin contains the amino acid cysteine ​​which gives red/yellow color tones, and pheoalanine is very abundant in large quantities in red hair and also contributes to the reddish color of freckles.

Eumelanin is the most common melanin in human skin and hair, and dark-skinned people have more eumelanin. Eumelanin colors hair from brown to black, and eumelanin is also the form of melanin that is usually missing in albinism.

All melanins are produced by melanocytes, which are a type of cell in our outermost skin layer (epidermis). Specifically, the 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, i.e. to the keratinocytes, these keratinocytes are the dominant cell type in our outermost skin layer.

Why is melanin so important?

Melanin's essential function is to protect our skin from harmful UV rays from sunlight. UV exposure is the biggest cause of skin cancer.

What is the difference between UVA and UVB rays?

You've probably heard of UVA and UVB rays, but here's a quick reminder of how different they are. UVA rays are the longer wavelength rays and represent the majority of UV radiation that reaches the atmosphere. UVB rays have shorter wavelengths and make up only a minority of UV radiation.

As the ozone layer is getting thinner, more and more UVB rays reach us, which is worrying considering that UVB rays are the most harmful and mutagenic (can cause mutations). UVA rays are also harmful to our genes, and UVA rays reach us even when we are sitting in the shade. The UVA rays penetrate deeper into the skin than the UVB rays do, and can have mutagenic effects in the dermis, i.e. the second layer of our skin that lies below the epidermis (the outermost skin layer).

Can UVA and UVB rays cause mutations in our DNA?

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 is not detected and repaired, the mutation multiplies as the cell divides. And if the mutation is in certain genes, it can lead to cancer.

In the two most common types of skin cancer, mutations associated with UVB damage are found in over 50% of patients.

How does melanin protect against UV rays and skin cancer?

Melanin protects our skin from light in several ways. It absorbs and redistributes the light energy from the UV rays, and it protects our genetic material (DNA) stored in the cell nucleus from the rays.

How are skin color, melanin and skin cancer connected?

Light-skinned people are about 70 times more likely to develop skin cancer than dark-skinned individuals, suggesting that pigmentation is a key factor in skin cancer. The difference is not in the number of melanin-producing melanocytes, but in the amount of melanin produced. Asian individuals have, on average, twice as much melanin as Caucasians, while Africans have about three to six times more melanin. Since the rate of skin cancer in light-skinned and dark-skinned people differs by a factor of 70, factors other than the amount of melanin are clearly contributing factors.

Another contributing factor may have to do with the lifespan of the melanosome. One study showed that melanosomes in dark-skinned people are more resistant to cell breakdown (when cells become too unstable in an organism, resulting in its eventual death) than in light-skinned individuals.

Is melanin a good sun protection factor?

Melanin, as sun protection has an SPF or sun protection factor. Scientists debate exactly how much SPF melanin has, but it's around SPF 1.5 - 2 and can be as high as 4. That might not sound like much, but an SPF 2 represents doubling the amount of protection from the sun. If you think about it another way, melanin absorbs around half of the UV light we are exposed to.

How does UV light affect skin pigmentation?

After DNA damage or repair from UV light exposure, the production of melanin is increased and this creates a tanned skin. How skin pigmentation is regulated is not well understood but will likely be the subject of future research. In mammals, more than 120 genes are known to have a role in pigmentation.

In other words; when the skin is exposed to the sun's UVB radiation, it gradually forms a pigment - melanin - which protects against mainly UVB radiation, and causes the skin to tan. This production of melanin is called melanogenesis. The increased production of melanin is a reaction to the DNA damage caused by UV radiation. Melanogenesis leads to delayed tanning, which typically becomes visible two or three days after exposure.

UVA radiation does not cause sunburn, but reaches deeper into the skin and can break down the connective tissue protein collagen , which among other things accelerates skin aging, and makes the skin wrinkled and inelastic.