Melanin and Melatonin shouldn’t be confused; despite their similar sounding names. Think of it like this: former colors your outside (skin, hair, eyes) while later regulates your inside (sleep, body clock)

Many people will tell you that genetics play a huge role in skin color, and that the sun can influence how much pigment the skin produces. But what layer specifically is responsible for skin pigment, and what are some of the differences you might see in the skin of someone with lighter skin versus someone with darker skin, and everywhere in between? The answer might surprise you.

Why do some people tan easily, while others burn? You also may have noticed that those with darker skin have a greater difference in the pigment of the palm of their hand compared to the dorsal aspect of their hand. These questions all revolve around melanin.

So let’s jump right into this!

What Is Melanin?

Melanin is a natural pigment found in the skin, hair, and eyes of humans and other animals. It’s produced by cells called melanocytes, which are located in the bottom layer of the skin’s epidermis. These melanocytes produce melanin through a complex chemical process called melanogenesis.

There are two main types of melanin:

• Eumelanin: This type of melanin is responsible for brown and black hues in skin, hair, and eyes. It’s the more protective form of melanin, offering better defense against UV radiation.
  
  
• Pheomelanin: This form gives rise to reddish and yellow hues, and is less effective at providing UV protection. People with lighter skin often have higher levels of pheomelanin, which is why they are more prone to sunburn.
  

Skin Structure

To fully appreciate skin color, we must explore the structure of the skin, which is part of the integumentary system. This system includes three main layers; the epidermis, dermis, and hypodermis (also known as the subcutaneous layer).

The Epidermis

The epidermis as in Epi” means upon, and “dermis” means skin is the thin, outermost layer of skin, measuring only about 0.1 to 0.15 mm thick—comparable to the thickness of a sheet of paper. However, in areas like the palms of the hands and soles of the feet, it can be much thicker, up to 4.5 mm. Despite its thinness, the epidermis plays a critical role in protecting the body and producing skin pigment.

The Dermis

Beneath the epidermis lies the dermis, which forms the majority of the skin’s thickness. The dermis is composed of dense connective tissue, giving the skin its strength and elasticity. This layer houses important structures such as hair follicles, glands, and blood vessels.

The Hypodermis

The hypodermis, or subcutaneous layer, consists mainly of adipose tissue (fat), which serves as an energy reserve and insulates the body. Although this layer is not considered part of the “true skin” (which includes only the epidermis and dermis), it plays an important role in the skin’s overall function.

Melanocytes: The Cells Behind Skin Pigment

In the epidermis, the key cells responsible for skin pigment are melanocytes, found in the stratum basale, the deepest layer of the epidermis. These cells produce melanin, the pigment that determines skin color, and interact with keratinocytes, which make up about 90% of the epidermis. Melanin not only gives skin its color but also helps protect against UV radiation.

Melanocytes distribute melanin to surrounding keratinocytes, and as the keratinocytes move upward through the layers of the epidermis from basale to corneum (the outermost layer of epidermis) they carry this pigment with them.

This process continues until the cells reach the skin’s surface and eventually shed, a cycle that contributes to the appearance and maintenance of skin pigment.

The Melanogenesis Process

The process of melanin production, or melanogenesis, is triggered by getting exposed to UV radiation. Here’s how it works:

• When the skin is exposed to the sun, UV radiation penetrates the epidermis and damages the DNA in skin cells. This damage triggers a protective response from melanocytes.
  
• In response to UV exposure, melanocytes produce melanin. The production process involves an enzyme called tyrosinase, which converts the amino acid tyrosine into melanin. The melanin is then transported into the skin cells, where it forms a protective shield around the nucleus to protect the DNA from further UV damage.
  
• In addition to protecting DNA, melanin also plays a role in skin repair. After sun exposure, melanin helps the body manage the damage by absorbing free radicals (unstable molecules that can cause cell damage) produced by UV radiation.
  

The Role of Genetics

Various genes influence skin color by regulating melanin production and distribution. For example, a gene called MC1R plays a crucial role in determining whether someone produces more eumelanin (darker pigmentation) or pheomelanin (lighter pigmentation).

Mutations in this gene can lead to red hair and fair skin, both of which are associated with higher levels of pheomelanin.

How Melanocytes Change Skin Color

As we have established by now, Melanocytes are the key cells responsible for giving our skin its color. They are found in the basal layer of the epidermis and interact with cells in the stratum spinosum, a layer above the basal that can be 8 to 10 cell layers thick.

Melanocytes have cytoplasmic extensions (like arms) that can contact up to 30 nearby keratinocytes, the primary cells of the epidermis. Through these extensions, melanocytes transfer melanin into the keratinocytes in both the stratum basale and stratum spinosum. The amount of melanin deposited into these cells is basically what determines the darkness of the skin.

Interestingly, although everyone has roughly the same number of melanocytes (about 8% of epidermal cells), the activity level of these cells varies.

People with darker skin have melanocytes that are more active, producing more melanin at a baseline level, while people with lighter skin have less melanin production.

Why The Palms and Soles Are Lighter in Color.

Well, the answer to that lies in the additional sublayers of the epidermis. Now, remember, we already talked about two sublayers of the epidermis: the stratum basale and the stratum spinosum. We’re going to add a couple more to help us understand these differences in form and function.

But let me mention one thing about the epidermis. The epidermis is an avascular tissue, meaning it doesn’t have a blood supply. There’s no room for blood vessels to penetrate between those cells.

Typically, we like cells to have a blood supply in order for them to stay alive. However, the dermis underneath the epidermis is where the epidermis sits on top of. It doesn’t have a blood supply.

The cells at the bottom, like those in the stratum Basale, which are the most mitotically active, are close enough to the blood to continue dividing and receiving nutrients. But as the cells get pushed further and further away from the blood supply, they start to flatten out.

That’s exactly what happens in the next sublayer we’re going to discuss, called the stratum granulosum. Yes, these cells are flattening out, but they’re also releasing little granules outside of themselves, essentially coating the cells in oil.

Now, why would these cells do that? Well, if you think about the mortal enemy of oil, it’s water. So, we’re creating a waterproofing barrier in the epidermis, preventing water from passing in and out. Kind of cool, right?

However, there’s no significant difference between them at this stage. The cells that have moved through the body shift into the typical granulosum layer. But when we reach the topmost layer, called the stratum corneum, those cells have fully flattened out and are completely dead.

You’ll have a stratum corneum layer all over your body. In some areas, it might be just a few cell layers thick, but on the soles of your feet, it can be up to 80 cell layers thick, contributing to that extra thickness. Now, imagine light trying to penetrate through those multiple layers.

I didn’t mention another sublayer called the stratum lucidum earlier. The stratum lucidum lies between the granulosum and corneum. The reason I didn’t bring it up initially is because it’s only found on the palms of the hands and the soles of the feet, nowhere else on the body.

“Lucidum” refers to being lucid, transparent, or full of light, and it adds additional thickness to the palms and soles. This extra thickness makes it harder for light to penetrate through, which makes sense when you look at your palms or the bottoms of your feet.

Fun Fact

Most of us don’t expose our palms to the sun very often. It’s just a natural position of how we hold our hands. They don’t get as much sun exposure as other parts of the body, which is why this thick layer on the palms doesn’t need to protect from UV rays as much.

It’s the same with most people—those with lighter skin might not notice the difference as much, but for people with darker pigments, the thicker areas on the palms and soles are more noticeable.

What is Tanning

Back to getting exposed to UV radiation, melanocytes ramp up melanin production as a defense mechanism. This increase in melanin helps protect the skin from harmful UV rays by absorbing them.

Over time, repeated sun exposure can lead to a darker skin tone, or tanning, as melanocytes respond by producing even more pigment to safeguard the skin.

However, this process is gradual, and the protection it offers is not immediate, which is why initial sun exposure often leads to burning before the skin tans.

Why Skin Tans Don’t Last

When we discuss tanning, whether viewed positively or negatively, it’s well-documented that fair-skinned individuals exposed to UV light are at greater risk of skin cancer. But why doesn’t a tan last?

After our beach day, where we soaked up the sun, our skin received temporary UV stimulation. Only the cells in the stratum spinosum and stratum basale received extra melanin deposits. As new cells are generated in the basal layer, they gradually push out the darker-pigmented cells responsible for the tan.

Eventually, these darker cells flake off. For those who prefer a lasting tan, consistent UV exposure is necessary to maintain it, those cautious of sun exposure, like myself, opt for high SPF sunscreen to avoid overstimulating melanocytes.

Conditions Affecting Melanin Production

While melanin production is generally stable, certain conditions can disrupt the normal function of melanocytes, leading to changes in skin pigmentation.

Albinism

Albinism is a genetic condition in which the body produces little to no melanin. This results in very light skin, hair, and eyes, and makes individuals with albinism highly sensitive to sun exposure.

Without melanin, they have almost no natural protection against UV radiation, which increases their risk of skin damage and cancer.

Vitiligo

Vitiligo is a condition where melanocytes are destroyed, leading to patches of skin that lose their pigment. The exact cause of vitiligo isn’t fully understood, but it’s believed to be an autoimmune disorder in which the body attacks its own melanocytes.

Freckles

Freckles and age spots are caused by the uneven distribution of melanin in the skin.

Types of Freckles

Ephelides

They typically inherited and more common in light-skinned individuals, appearing as small, light-brown spot.

Lentigines

Lentigines, on the other hand, are often related to sun exposure and can appear as larger, darker spots on the skin due to localized melanin build.

Protecting Your Skin: Tips for All Skin Types

No matter your skin tone, protecting your skin from the harmful effects of the sun is crucial. While melanin provides some defense against UV radiation, it’s not enough on its own, especially with prolonged exposure.

Here are some practical tips for protecting your skin:

1. Use Sunscreen: Apply broad-spectrum sunscreen with an SPF of at least 30 whenever you’re outdoors. Reapply every two hours, especially if you’re swimming or sweating.
   
   
2. Wear Protective Clothing: Long sleeves, hats, and sunglasses can provide additional protection, especially during peak sun hours.
   
   
3. Seek Shade: Avoid direct sun exposure between 10 a.m. and 4 p.m., when UV rays are strongest.
   
   
4. Check Your Skin Regularly: Be aware of any changes in your skin, such as new moles, spots, or areas of discoloration. Early detection of skin cancer significantly increases the chances of successful treatment.
   
   
5. Moisturize and Hydrate: Keeping your skin hydrated helps maintain its barrier function, which is essential for overall skin health.
   

Conclusion

Melanin is far more than just a pigment—it’s a vital part of our body’s defense system. By understanding how melanin works, we gain insights into the biology of skin color, the importance of sun protection, and the role this incredible molecule plays in our health.

Whether you’re light-skinned, dark-skinned, or somewhere in between, melanin is working behind the scenes to protect your skin and body from the harmful effects of the sun.

So, next time you think about your skin color, remember the amazing science behind it. Melanin is not just a pigment—it’s a powerful protector that has evolved over millennia to help us survive in the environments we live in today.