There is no clear reason as to the causes of mole. However, it is thought due to be caused by the defect during the embryonic development stage. During the organ formation stage, the organogenesis, that is the first trimester or the first 12 weeks, there is a defect caused by the proliferation of pigment cell, the melanocyte. Such cell is been produced at an extremely faster rate. The resultant causing the pigment cell to form cluster instead of spreading out in the normal development. This causes abnormal clumping of cell in an area called the nevus/mole.
The genetic factor is thought to be another cause of face mole.
This is indicated in the dysplastic nevi and the atypical mole syndrome, both of which are the heredity disease, causes the patient to have a big number of moles, frequently more than 100. This greatly increased the chance of developing melanoma.
It should be noted that the dysplastic nevi/mole is extremely common. Many people have at least a few of such abnormal moles/nevi. Having more than 4 carries a significantly increased risk of getting a melanoma.
In the general population, most of the melanoma do not form from a pre-existing mole. Rather, they form from a new lesion on the skin.
The UV ray from the sun has the power to cause skin aging prematurely, and even cause melanoma. It is believed that sun exposure may cause the acquired mole.
Sunburns increases the risk factor for melanoma. The strategy is to avoid the sun between 10 am to 4 pm. Also, stay covered at all-time using broad brimmed hat, long sleeve, long trouser, and sunblock and sun glasses.
The big hormonal changes during the pregnancy and even the diabetes (insulin hormone) is thought to contribute to the mole formation.