A mole, also known as a nevus, is a common skin growth. These spots form when pigment-producing cells, called melanocytes, cluster together on the skin. While some moles are present at birth, most develop throughout childhood and adolescence. The idea that moles simply “appear out of nowhere” is a common misunderstanding; they develop over time or become more noticeable due to various factors.
The Biology of Mole Formation
Moles form when melanocytes, the cells responsible for producing melanin, the pigment that gives skin its color, grow in groups instead of spreading evenly across the skin. These clusters of melanocytes create the visible spots we recognize as moles. Melanin also plays a role in protecting the skin from ultraviolet (UV) radiation.
Genetic factors influence the number of moles an individual may develop. Sun exposure also plays a role in their formation by stimulating melanocytes to produce more melanin and cluster together. While moles can appear anywhere on the body, they are frequently found on areas exposed to the sun, such as the face, arms, neck, and back.
Why Moles Seem to Emerge Suddenly
The perception of moles “appearing suddenly” often arises because tiny, previously unnoticed moles can slowly grow or darken over time, becoming more visible. Hormonal changes are a factor in this phenomenon. Fluctuations during puberty, pregnancy, and menopause can stimulate melanocytes, leading to the formation of new moles or changes in existing ones. For instance, pregnancy hormones can cause existing moles to darken.
Accumulated sun exposure throughout life can also cause moles to become more prominent. UV radiation from the sun can trigger the growth of melanocytes, leading to the development of new moles even in adulthood. Therefore, while a mole may seem to appear spontaneously, it is often a result of gradual biological processes.
When to Monitor New or Changing Moles
It is helpful to regularly examine your skin for any new moles or changes in existing ones. A widely used guideline for identifying potentially concerning moles is the ABCDE rule. This acronym stands for Asymmetry, Border irregularity, Color variation, Diameter, and Evolving.
- Asymmetry: One half of the mole does not match the other.
- Border irregularity: Edges are uneven, ragged, notched, or blurred.
- Color variation: Multiple shades within the same mole (e.g., browns, blacks, red, white, or blue).
- Diameter: Moles larger than 6 millimeters (about the size of a pencil eraser).
- Evolving: The mole has changed in size, shape, color, or elevation, or if it starts to itch, bleed, or become tender.
Any mole exhibiting these characteristics or any “ugly duckling” mole that looks different from others on your skin should be evaluated by a healthcare professional.