Melanoma starts in the melanocytes, the melanin-producing cells that give skin its color. In the healthy process of skin cell development, older cells die off, at the skin’s surface, and are replaced by new, healthy cells. Melanoma begins when something goes wrong in the process, causing damaged melanocytes to grow out of control, forming a cancerous mass.

According to the Mayo Clinic, “approximately 70 percent of [melanoma] cancers arise from normal-appearing skin, while the remaining 30 percent arise from an existing mole.”

While it’s still unclear what, exactly, damages DNA in skin cells, experts point to a number of factors. The leading contributor to damaged cells and melanoma development was long considered to be over-exposure to ultraviolet (UV) radiation from the sun and artificial sources, such as tanning beds and lamps. While UV radiation still poses a serious risk, UV light—alone—is no longer thought to contribute to all melanoma development. As the Mayo Clinic points out, “UV light doesn’t cause all melanomas, especially those that occur in places on your body that don’t receive exposure to sunlight” suggesting a combination of factors in melanoma development.

Other causes of melanoma may include:

  • genetics
  • environment
  • age