Skin Pigmentation: Melanin, Carotene, Hemoglobin (OpenStax Anatomy and Physiology)
The color of skin is influenced by a number of pigments, including melanin, carotene, and hemoglobin. Melanin is produced by cells called melanocytes, which are found scattered throughout the stratum basale of the epidermis. The melanin is transferred into the keratinocytes via a cellular vesicle called a melanosome.
- Keratinocyte are one of the major cell types of the epidermis that help to maintain a mechanical barrier and are actively involved in all phases of the autoimmune response in the skin.
- Melanosomes are lysosome-related organelles within which melanin-producing enzymes are present and where melanin is produced.
Melanin occurs in two primary forms. Eumelanin exists as black and brown, whereas pheomelanin provides a red color. Dark-skinned individuals produce more melanin than those with pale skin. Exposure to the UV rays of the sun or a tanning salon causes melanin to be manufactured and built up in keratinocytes, as sun exposure stimulates keratinocytes to secrete chemicals that stimulate melanocytes. The accumulation of melanin in keratinocytes results in the darkening of the skin, or a tan. This increased melanin accumulation protects the DNA of epidermal cells from UV ray damage and the breakdown of folic acid, a nutrient necessary for our health and well-being. In contrast, too much melanin can interfere with the production of vitamin D, an important nutrient involved in calcium absorption. Thus, the amount of melanin present in our skin is dependent on a balance between available sunlight and folic acid destruction, and protection from UV radiation and vitamin D production.
It requires about 10 days after initial sun exposure for melanin synthesis to peak, which is why pale-skinned individuals tend to suffer sunburns of the epidermis initially. Dark-skinned individuals can also get sunburns, but are more protected than are pale-skinned individuals. Melanosomes are temporary structures that are eventually destroyed by fusion with lysosomes; this fact, along with melanin-filled keratinocytes in the stratum corneum sloughing off, makes tanning impermanent.
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.
Betts, J. G., Young, K. A., Wise, J. A., Johnson, E., Poe, B., Kruse, D. H., … DeSaix, P. (n.d.). Anatomy and Physiology. Houston, Texas: OpenStax. Access for free at: https://openstax.org/details/books/anatomy-and-physiology
Related External Link: Genetic ancestry, skin color and social attainment: The four cities study
Research Article: Key Regulatory Role of Dermal Fibroblasts in Pigmentation as Demonstrated Using a Reconstructed Skin Model: Impact of Photo-Aging
Date Published: December 9, 2014 Publisher: Public Library of Science Author(s): Christine Duval, Catherine Cohen, Corinne Chagnoleau, Virginie Flouret, Emilie Bourreau, Françoise Bernerd, Andrzej T. Slominski. http://doi.org/10.1371/journal.pone.0114182 Abstract: To study cutaneous pigmentation in a physiological context, we have previously developed a functional pigmented reconstructed skin model composed of a melanocyte-containing epidermis grown on a dermal … Continue reading
Research Article: Genome-Wide Association Studies of Quantitatively Measured Skin, Hair, and Eye Pigmentation in Four European Populations
Date Published: October 31, 2012 Publisher: Public Library of Science Author(s): Sophie I. Candille, Devin M. Absher, Sandra Beleza, Marc Bauchet, Brian McEvoy, Nanibaa’ A. Garrison, Jun Z. Li, Richard M. Myers, Gregory S. Barsh, Hua Tang, Mark D. Shriver, Nicholas John Timpson. http://doi.org/10.1371/journal.pone.0048294 Abstract: Pigmentation of the skin, hair, and eyes varies both within and … Continue reading
Research Article: Coordinated Regulation of Chromatophore Differentiation and Melanogenesis during the Ontogeny of Skin Pigmentation of Solea senegalensis (Kaup, 1858)
Date Published: May 9, 2013 Publisher: Public Library of Science Author(s): Maria J. Darias, Karl B. Andree, Anaïs Boglino, Ignacio Fernández, Alicia Estévez, Enric Gisbert, Andre van Wijnen. http://doi.org/10.1371/journal.pone.0063005 Abstract: Abnormal pigmentation of Senegalese sole has been described as one problem facing the full exploitation of its commercial production. To improve our understanding of flatfish pigmentation … Continue reading