The color of skin and other bodily structures is influenced by a number of pigments, including melanin, hemoglobin, and carotene, among others. Differences in the color of skin can be based on genetics, disorders or conditions, nutrition, injuries, or the environment. In this lesson, you will learn about some of the different types of pigmentation in the human body.
2. Melanin
Recall that melanin is a protein pigment produced by cells called melanocytes, which are found scattered throughout the stratum basale of the epidermis. The number of melanocytes present in the skin is the same no matter a person’s skin or hair color. The difference is in how much melanin a melanocyte produces. Dark-skinned individuals produce more melanin than those with pale skin.
Skin Pigmentation—The relative coloration of the skin depends on the amount of melanin produced by melanocytes in the stratum basale and taken up by keratinocytes.
Melanin is produced by melanocytes and transferred into keratinocytes by a vesicle called a melanosome. Recall that melanin can act as a shield to protect a cell from the damaging effects of UV light which can cause DNA mutations. Exposure to the UV rays of the sun or a tanning salon causes keratinocytes to secrete chemicals that stimulate melanocytes to increase melanin production. The accumulation of melanin in keratinocytes results in the darkening of the skin, or a tan. However, it requires about 10 days after initial sun exposure for melanin synthesis to peak, which is why pale-skinned individuals tend to initially suffer sunburns of the epidermis. Dark-skinned individuals can also get sunburns but are more protected than pale-skinned individuals.
Suntans are also impermanent for two reasons. First, melanosomes are eventually destroyed by fusion with lysosomes which will break down the melanin. Second, the skin is continually renewed as the stratum corneum sloughs off.
Too much sun exposure can eventually lead to wrinkling due to the destruction of the cellular structure of the skin and, in severe cases, can cause sufficient DNA damage to result in skin cancer. When there is an irregular accumulation of melanocytes in the skin, freckles appear. Moles are larger masses of melanocytes, and although most are benign, they should be monitored for changes that might indicate the presence of cancer. You will learn more about skin cancer and associated changes in a future lesson.
Moles—Moles range from benign accumulations of melanocytes to melanomas (skin cancer). These structures populate the landscape of our skin.
While melanin can protect cells from harmful DNA damage, too much melanin can have detrimental effects. Through UV light exposure, the skin plays a role in the production of Vitamin D, an important nutrient involved in calcium absorption. Therefore, too much melanin can lower Vitamin D and calcium levels in the body. You will see in a future lesson how this can affect the structural integrity of bones and the skeletal system.
IN CONTEXT
Melanin-Associated Disorders
The first thing a clinician sees is the skin, so the examination of the skin should be part of any thorough physical examination. Most skin disorders are relatively benign, but a few, including melanomas, can be fatal if untreated. A couple of the more noticeable disorders, albinism and vitiligo, affect the appearance of the skin and its accessory organs. Although neither is fatal, it would be hard for the afflicted individuals to claim that they are benign.
Albinism is a genetic disorder that affects (completely or partially) the coloring of skin, hair, and eyes. The defect is primarily due to the inability of melanocytes to produce melanin. Individuals with albinism tend to appear white or very pale due to the lack of melanin in their skin and hair. Recall that melanin helps protect the skin from the harmful effects of UV radiation. Individuals with albinism tend to need more protection from UV radiation, as they are more prone to sunburns and skin cancer. They also tend to be more sensitive to light and have vision problems due to the lack of pigmentation on the retinal wall. Treatment of this disorder usually involves addressing the symptoms, such as limiting UV light exposure to the skin and eyes.
In vitiligo, the melanocytes in certain areas lose their ability to produce melanin, possibly due to an autoimmune reaction. This leads to a loss of color in patches (see image below).
Neither albinism nor vitiligo directly affects the lifespan of an individual.
Individuals with vitiligo experience depigmentation that results in lighter-colored patches of skin. The condition is especially noticeable on darker skin.
terms to know
Melanin
A protein pigment produced and secreted by a melanocyte.
Melanocyte
A pigment-producing cell found in the stratum basale responsible for skin and hair color.
Melanosome
A cellular vesicle that transports melanin from melanocytes into keratinocytes.
3. Hemoglobin
Hemoglobin (Hg) is the protein pigment that provides blood the ability to carry and transport oxygen throughout the body. When blood is oxygenated, hemoglobin is bright red, and the blood vessels carrying it are seen as red. When oxygen is used up, the blood is deoxygenated, hemoglobin is dark red, and the blood vessels are seen as blue (a trick your skin plays with light).
Blood—Blood changes color depending on how much oxygen is bound to hemoglobin. Oxygenated blood is bright red (left), while deoxygenated blood is dark red (right).
did you know
When the body sends additional oxygenated blood to an area of skin, it adds red to its natural color. This occurs during blushing, embarrassment, or inflammation. When blood is moved out of a region of the body, it takes away the red, causing a pale-skinned person to turn white. This occurs with very low blood pressure, poor peripheral circulation such as Reynauds, or when a person is “scared white.” Lastly, if the blood in a region of the body turns from oxygenated to deoxygenated, the skin will turn bluish, a condition called cyanosis. This occurs when blood is not allowed to leave an area, such as a tourniquet or bruise.
Blood and Skin Color—The blood present underneath the skin plays a role in its color. (a) The presence of extra oxygenated blood can turn the skin red, such as when you blush. (b) The lack of blood can turn the skin white, such as during poor peripheral circulation. (c) The presence of deoxygenated blood can turn the skin blue.
When hemoglobin is broken down, it changes colors. This can occur naturally in the body or underneath the skin in a bruise. Below is a quick list of the colors hemoglobin can cause in a bruise (and the body).
Red = oxygenated hemoglobin
Blue = deoxygenated hemoglobin
Purple = mixed oxygenated and deoxygenated blood
Yellow = hemoglobin broken down (bilirubin, urobilin), makes urine yellow
Brown = hemoglobin broken down (stercobilin), makes feces (poop) brown
Green = hemoglobin broken down (bile), makes bile green
Hemoglobin‘s Many Colors—Hemoglobin can provide a variety of colors depending on its oxygen status or breakdown status. All of these colors are naturally found in the body in blood, bile, urine, or feces but can also be found in a bruise.
term to know
Hemoglobin
A red protein pigment in the blood that binds oxygen.
4. Other Pigments
Other changes in the appearance of skin coloration can be indicative of dietary practices or diseases associated with other body systems.
Carotene, a green, yellow, orange, or red pigment in many vegetables, can be stored in adipose tissue. Excessive consumption of these pigments can alter skin tone.
Liver disease or liver cancer can cause the accumulation of bile and the yellow pigment bilirubin (a breakdown product of hemoglobin), leading to the skin appearing yellow or jaundiced (jaune is the French word for “yellow”).
Tumors of the pituitary gland can result in the secretion of large amounts of melanocyte-stimulating hormone (MSH), which results in a darkening of the skin.
Addison’s disease can stimulate the release of excess amounts of adrenocorticotropic hormone (ACTH), which can give the skin a deep bronze color.
did you know
Many additional substances, if consumed or applied topically, can have an effect on the color of your skin, including silver. Start by looking up the condition of argyria. You can also look up a photo of Paul Karason, who went by “Blue Man” or “Real Papa Smurf.”
Paul Karason had what he described as a bad case of dermatitis, inflammation of the dermis in his skin that affected his face. After many different treatments that didn’t work, Paul decided to try his own remedy, silver. Silver has some antimicrobial properties that some claim to be beneficial to the body. He began applying silver to his skin as a topical agent. Over time, he found that his dermatitis improved. He eventually began making a solution of silver and water that he drank as well. While the treatment seemed to help his skin as well as other ailments (arthritis, acid reflux, etc.), his skin began to turn blue.
We think of silver as a silver color. However, when a silver salt (an ionically bonded compound) has light applied to it, it turns into a bluish hue. This is a known process used in photography but also seems to be how the body processes silver when taken into the body. Silver is converted into a salt when absorbed, but when stored in the adipose tissue of the hypodermis, it is converted back to elemental silver by light, giving off its blue tint.
For people who turn blue due to silver, it is a condition called argyria. This condition is permanent and cannot be reversed. In 1999, the Food and Drug Administration (FDA) made a ruling stating that “all over-the-counter (OTC) drug products containing colloidal silver ingredients or silver salts for internal or external use are not generally recognized as safe and effective.”
summary
In this lesson, you learned about pigmentation in the human body. Specifically, you learned about how melanin is a pigment that produces the pigmentation of human skin, hair, and eyes. You then learned that hemoglobin is red protein pigment that provides blood the ability to carry and transport oxygen throughout the body, and you learned about the color changes that occur when hemoglobin is broken down. Finally, you learned about the effects of other pigments that can result in changes in the appearance of skin coloration.
