At the bottom layer of the epidermis are melanocytes, cells that produce a brown pigment: melanin. This pigment accumulates in the keratinocytes and darkens the skin. The process of melanogenesis is responsible for long-term pigmentation that's designed to protect the epidermis from UV-B radiation damage and ensure the functionality of other organs and tissues. Researchers have found melanin also plays a role in the immune system and the ongoing health of vital systems in the body.
Skin color variations are adaptation mechanisms, according to natural history research. As humans moved around hot environments looking for food, the body had to make certain changes to cool itself. This need for thermoregulation led to an increase in the number of sweat glands and a decrease in body hair, which in turn left the skin more exposed to the intense sun, especially in locations near the equator. Darker pigmentation was a natural sunscreen. Those who lived in colder climates developed lighter skin because they had to deal with lower UV radiation and needed skin that allowed sunlight to help the body to produce vitamin D naturally.
Eumelanin is the pigment that ranges from brown to black. It's dominant in hair, eyes, and skin and offers greater protection against UV radiation damage. Pheomelanin is an orange to red pigmentation that's also present in hair and skin. Those with red hair, for example, or naturally red lips, have more concentrated doses of pheomelanin.
Neuromelanin is a dark pigment in the brain that gives color to neurotransmitting cells. The Czech anatomist Jan Evangelista Purkyne first described this pigment in the substantia nigra in 1838. No one thought it had any function until recent studies investigated how the loss of neuromelanin relates to the progression of Parkinson's disease. It's possible that just like melanin protects the skin from damage, neuromelanin protects against cell death.
Oculocutaneous albinism is an inherited disorder that results in insufficient or a complete lack of pigmentation in the skin, hair, and eyes. Albinism has a better chance of occurring when both parents have the recessive genetic disorder, and it can occur in any ethnicity, to varying degrees. Those with this kind of disorder have skin that's highly prone to sun damage and cancer, as well as vision abnormalities including involuntary eye movements and sensitivity to light. Those with albinism need to wear sunglasses to protect their eyes and sunscreen on their skin whenever they are in natural light.
When certain parts of the skin lose pigment, the result is vitiligo -- noticeable patches of white (pigment-less) skin. Vitiligo is most visible in darker-skinned people and usually manifests between the ages of 20 and 30. While the cause behind the destruction of those particular melanocytes remains unclear, there are three possible depigmentation patterns:
Another cause of hypopigmentation is skin trauma, such as burns or blisters. Depending on the degree, the loss of melanin may be severe. Treatment for this type of hypopigmentation includes the use of cosmetics to camouflage or corticosteroid creams. The good news is that pigment loss may not be permanent, but it will take time to redevelop.
Overproduction of melanin is a common condition across all skin types and can occur anywhere in the body. One way it manifests is the appearance of sun spots or liver spots on sun-exposed skin. Treatments can often reduce or remove these largely harmless spots if they make people feel self-conscious. Freckles are an inherited feature that becomes more prominent with more sun exposure during the hotter months. Melasma is the presence of brown patches on the skin, particularly on the face. It's more common in women during pregnancy, because it is triggered by hormones.
The amount of pigment in the stroma of the iris determines eye color. Those with little or no pigment tend to have blue irises. With slightly more pigment, eye color is green, and eyes with lots of melanin are brown. Lighter colored eyes tend to be more sensitive to sunlight and are at greater risk of other problems, including macular degeneration. By comparison, individuals with darker eyes may be at higher risk of cataracts or glaucoma.
For those who want to remove unwanted skin pigmentation, there are plenty of over-the-counter products, as well as skin care professionals who can prescribe the right medicines for patients. But there are also unregulated bleaching products that can damage the skin. Some contain unsafe levels of hydroquinone, which can cause ochronosis, an untreatable form of skin discoloration. Prolonged use of these bleaching creams may prematurely age skin, thin it out, or cause an allergic reaction. And, depending on where the product comes from, some bleaching creams contain toxins such as mercury.
Melanoma is cancer that begins in the melanocytes. It usually starts as a dark mole on the skin that increases in size. There are four types of melanoma. Superficial spreading is the most common. A nodular melanoma becomes red as it grows quickly on the chest, back, neck, or head. Lentigo maligna is less common and found primarily in older people with a lot of sun exposure over the years. Acral lentiginous is the rarest form, found in the nails, palms of the hands, and soles of the feet.
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