The formation of melanocytic nevi, commonly known as moles, is heavily influenced by genetic factors. If there is a family history of numerous moles, other family members are also likely to have them.
Ultraviolet (UV) exposure is a major environmental factor in the formation of moles. UV radiation can stimulate melanocytes to increase melanin production, leading to darker skin and the formation of moles.
Hormonal changes during pregnancy or from taking medications containing sex hormones can affect melanocyte activity, sometimes leading to the formation of new moles or darkening of existing ones.
After skin injury, the body may form moles as part of the healing process, in response to the damage.
As people age, they may naturally develop more moles as part of the skin's aging process.
Skin type can also influence the formation of moles. For example, individuals with lighter skin may be more prone to developing moles.