New moles appearing: is this normal?

The moles, or nevi, can form on any part of the body and take on different sizes, shapes, and colors. Their appearance is caused by an abnormal grouping of melanocytes, the cells that synthesize melanin during the melanogenesis process to help the skin protect itself from the sun. This cluster of melanocytes in a localized area of the skin is responsible for the pigmented nature of moles. Even though most nevi are benign, some can evolve and pose a risk of melanoma. That's why it's essential to monitor their appearance and be attentive to their evolution.

It is uncommon to be born with moles: the majority form during childhood. Therefore, it is entirely normal to notice new nevi during this period.

The emergence of new skin spots is primarily due to repeated exposure to UV rays from the sun. Indeed, these rays stimulate the differentiation and proliferation of melanocytes, thereby increasing the risk of nevi. It is thus normal for children to notice new skin spots on parts of the body often exposed to the sun, such as the face, arms, and legs. This is particularly the case for individuals with light skin, eyes, and hair, who are naturally less protected due to producing less melanin.

Besides sun exposure, certain hormonal changes can also promote the appearance of new moles. This is particularly the case during puberty, a period when hormones influence the activity of melanocytes and can induce the formation of new nevi or alter the appearance of those already present. Pregnancy is another life stage rich in hormonal upheavals, marked among other things by an increase in estrogen levels in the body. Indeed, estrogens act by increasing the release of the α-MSH hormone by the pituitary gland, a peptide involved in stimulating melanocytes through their MC1R receptor. This activation leads to an intensification of melanin synthesis and can result in the appearance of new moles or changes in existing nevi. A study involving 100 pregnant women recently showed that during their pregnancy, 35% of them had observed changes in their moles or the formation of new ones.

Apart from these specific situations, new moles in adulthood are rare and it is recommended to have them examined to rule out any risk of melanoma.

This is particularly true for moles that are atypical, meaning those that have an irregular shape, poorly defined edges, uneven color, or a diameter larger than 6 mm, as well as those that change over time in appearance, size, or texture. To identify moles that should raise concern, it is helpful to refer to the ABCDE method (A for Asymmetry, B for Borders, C for Color, D for Diameter, and E for Evolution).