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What changes in melanocytes cause skin to tan after sunlight exposure?

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Learn how regenerative properties of the skin helps to protect the human body from the external environment — human skin Human skin, whose cells are generated continuously by the body, serves as a protective barrier between the inside of the human body and the environment.

When skin is exposed to sunlight, the process of tanning occurs through changes in the activity of melanocytes rather than an increase in their number.1

These specialized cells, located in the epidermis, respond to ultraviolet radiation by increasing their production of melanin, the pigment responsible for skin darkening. This process is often stimulated by the release of melanocyte-stimulating hormone (MSH), which binds to receptors on the melanocytes to trigger increased pigment synthesis.213

Once produced, the melanin granules are transferred via the melanocytes' branching dendrites to neighboring keratinocytes. Inside these cells, the pigment granules orient themselves above the nucleus to form a protective shroud, which helps shield the cell's DNA from further damage caused by ultraviolet rays. This natural defense mechanism is a temporary response; as the cells containing the pigment migrate to the surface and eventually die, the tan fades.214