How Moles Develop

Layers of the Skin


The First Layer: Epidermis

The thin top layer of skin we can see with the naked eye. A waterproof barrier that protects us from bacteria and other microscopic organisms in the environment.

Cells within the epidermis:

  • Keratinocytes are specialized skin cells that make up most of the epidermis. The outermost part of the epidermis is made up of keratinocytes that have lost their nucleus, are full of a protein called keratin that makes them hard, and link together to form a waterproof barrier. Keratinocytes are constantly shed and replaced by squamous cells that turn into keratinocytes as they migrate up to the top of the skin.
  • Squamous cells are live keratinocytes that make keratin, an important skin protein.
  • Basal cells make up most of the basal layer, the innermost layer of the epidermis. They are the only cells in the epidermis that divide and create new cells called keratinocytes.
  • Melanocytes are located in the basal layer of the epidermis. They are interspersed regularly between the basal cells. Melanocytes produce melanin, a pigmented protein that gives us our skin and hair color and provides protection against the damaging effects of ultraviolet radiation.

The Second Layer: Dermis

The thicker, second layer of skin located beneath the epidermis. Contains blood and lymph vessels, nerve endings, muscle fibers, oil and sweat glands, and hair follicles

There are 2 layers within the Dermis:

  • Papillary dermis, the upper layer
    • Made of loose connective tissue, blood vessels, and nerves. Fingerlike projections called papillae connect the dermis to the epidermis and provide the epidermis with vital nutrients.
  • Reticular dermis, the thicker lower layer
    • A network of collagen fibers, dense connective tissue that gives skin its elasticity and strength
    • Contains a rich supply of blood vessels and nerves, as well as lymph vessels, glands, and hair follicles

The Bottom Layer: Subcutaneous Layer or Subcutis

A thick layer of fat and connective tissue beneath the dermis

  • Like the dermis, it contains a rich supply of blood and lymph vessels.
  • It insulates and saves your body heat, acts as a shock absorber to protect your underlying tissues and organs from injury, and is a source of reserve energy.

Melanocytes and Melanin

Melanocytes are cells located in the lower part of the epidermis, just above the dermis. They make the pigment called melanin, which gives color to the skin, hair, and parts of the eye.

Melanin protects the skin from ultraviolet (UV) radiation, the harmful rays of the sun.

benign-lesions-(lesions-that-are-not-cancerous)-melanocytes-and-melanin-melanin-protects-the-skin-from-uv-radiationMoles or Clusters of Melanocytes

A mole is a cluster of melanocytes that appears as a pigmented spot on the skin.

  • Moles can be either flat or raised, round or oval, and are usually smaller than a pencil eraser.
  • Although generally benign and unchanging, moles can sometimes become cancerous.
  • The first sign of melanoma is often a change in the size, shape, or color of an existing mole or the appearance of a new mole in adulthood. (See Moles and Other Lesions for more information.)

Both light- and dark-skinned people have the same number of melanocytes. The differences in skin color are the result of differences in the amount of melanin and the size of the melanin “packets” that each melanocyte makes.

  • Pheomelanin is a red-yellow pigment most often found in fair-skinned people with red hair. Some red-haired people appear to not have any moles, because theirs are pink to red, not brown.
    • People with more eumelanin are more likely to tan and to
      be protected from UV radiation.
    • People with less eumelanin are more likely to freckle or burn.
  • Eumelanin, the most plentiful of human melanin, is found in brown and black skin and hair.
  • Albinos are unable to produce normal quantities of melanin and so have reduced levels or an absence of pigment in their skin, hair, and eyes.

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