A mole (nevus) is a common skin growth resulting from a cluster of pigment-producing cells called melanocytes. Most people will develop between 10 and 40 moles over their lifetime, and the majority of these growths are entirely harmless. New moles can and often do continue to form after youth, although the rate of appearance is much slower than in childhood. While the appearance of a new spot in adulthood is usually benign, it warrants close attention because new growths are more likely to be cancerous than older, long-established moles.
The Typical Timeline of Mole Formation
Most common moles appear during childhood and adolescence. Most people will have acquired their full complement of moles by the time they reach their early twenties, though development can continue up to about age 40.
A mole’s existence follows a natural life cycle that can last around 50 years. Initially, a mole may appear flat and dark, but over decades, it may enlarge, become raised, lighten in color, and even develop hairs. Eventually, many moles will slowly fade away or disappear entirely as a person ages into their later years.
Triggers for New Moles in Adulthood
Even after the peak formation years have passed, several factors can stimulate the melanocytes to form new moles in adulthood. One of the most significant influences is cumulative ultraviolet (UV) exposure from the sun or tanning beds. The interaction of UV light with the skin’s DNA causes damage that can trigger the development of new moles, sometimes years after the exposure occurred.
Hormonal fluctuations are another common trigger for late-onset moles, often seen in women. New moles may appear or existing ones may darken and enlarge during times of major hormonal change, such as pregnancy. Certain medications can also affect the immune system or hormone levels, sometimes leading to the unexpected development of new skin spots.
Genetics play a determining role in a person’s overall predisposition to forming moles throughout life. Individuals with a family history of numerous or atypical moles may be more likely to see new growths even as adults. These late-appearing moles result from an interplay between inherited traits and lifetime environmental exposures.
Identifying Moles That Need Medical Attention
While most new moles in adulthood are not cancerous, any new growth or change in an existing one after the age of 20 should prompt closer monitoring. Self-examination should be performed monthly to track any changes or new lesions. A helpful guide for assessing any suspicious spot is the ABCDE method, which identifies five characteristics associated with melanoma.
- Asymmetry: One half of the mole does not match the other half in shape.
- Border irregularity: The edges are uneven, notched, or blurred instead of smooth and well-defined.
- Color variation: The mole contains multiple shades of color, such as different tones of brown, black, white, red, or blue.
- Diameter: The mole is larger than 6 millimeters, roughly the size of a pencil eraser.
- Evolving: Any change over time in the mole’s size, shape, color, or height, or the onset of new symptoms like itching, bleeding, or crusting.
It is important to contact a dermatologist if you notice any of the ABCDE warning signs, or if a new lesion appears that looks significantly different from your other established moles. Even if a new mole does not fit the classic ABCDE criteria, any new growth that develops after age 50 or any mole that begins to bleed or itch must be evaluated immediately. Early detection of melanoma, which can arise from a new mole, significantly improves the chances of successful treatment.