A mole, medically known as a nevus, is a common skin growth composed of melanocytes, cells responsible for producing melanin, the skin’s natural pigment. While the perception of a mole “popping up overnight” is common, these growths typically develop gradually over time. New spots can appear, and understanding their formation, sudden appearance, and when to seek medical attention is important.
How Moles Form
Moles form when melanocytes, pigment-producing cells, cluster instead of spreading evenly, creating a visible spot. Most individuals develop between 10 and 45 moles during their lifetime, with the majority appearing during childhood and adolescence.
Genetic predisposition plays a role in the number and type of moles an individual develops. Additionally, exposure to ultraviolet (UV) radiation from the sun or tanning beds can influence mole formation and increase their number. While some moles may be present at birth, known as congenital nevi, most are acquired over time. The “overnight” appearance of a mole is often a misperception; a small, flat mole might have been present but unnoticed, only becoming visible as it grows slightly, darkens, or becomes raised.
Why New Spots Seem to Appear Suddenly
Many factors contribute to the sudden appearance of new skin spots, most of which are benign. Small, previously unnoticed moles can grow larger or darken, making them more apparent. This growth can be subtle and then seem sudden once a certain size or pigmentation threshold is reached.
Sun exposure frequently triggers new skin spots, including freckles, sunspots (lentigines), or moles. Hormonal fluctuations can also cause existing moles to darken or new benign growths to form, often seen during puberty, pregnancy, or with certain medications.
Besides true moles, other common, non-cancerous growths can emerge somewhat suddenly. Seborrheic keratoses, which are waxy, scaly, and slightly raised growths, often appear gradually but can seem to develop quickly, particularly in middle age or later. Cherry angiomas, small, bright red spots resulting from benign overgrowths of blood vessels, can also appear rapidly on the skin. Sometimes, what appears to be a new mole is actually an inflammatory reaction, such as a pimple or an insect bite, which can initially mimic the appearance of a new skin growth. While these newly appearing spots are generally harmless, any new or changing spot warrants careful observation.
When a New Spot Needs Medical Attention
While many new or changing skin spots are benign, it is important to recognize signs of more serious conditions like melanoma, a type of skin cancer. Early detection of melanoma is important for successful treatment. Dermatologists use the “ABCDE” rule as a guide to identify potentially concerning moles or new growths.
Asymmetry (A) means that one half of the mole does not match the other half if an imaginary line were drawn through it. Border (B) irregularity refers to edges that are uneven, notched, or blurred, rather than smooth. Color (C) variation within a single mole, or the presence of multiple colors like shades of brown, black, red, white, or blue, is another warning sign. Diameter (D) greater than 6 millimeters, roughly the size of a pencil eraser, raises concern, although melanomas can sometimes be smaller.
Finally, Evolving (E) refers to any change in the mole’s size, shape, color, or elevation, or the development of new symptoms such as itching, tenderness, bleeding, or crusting. Any new spot that exhibits these characteristics, or any existing mole that changes rapidly or causes new symptoms, should be evaluated by a healthcare professional, ideally a dermatologist.