The sudden growth of a mole on the left thumb may be caused by abnormal embryonic differentiation, or it may be caused by local stimulation by drugs, ultraviolet rays or trauma.
Many patients with congenital nevus of pigmentation are due to abnormal cell differentiation during embryonic period, which leads to local melanin accumulation and produces nevus of pigmentation, and this kind of nevus is usually present at birth or appears within a few days after birth.
The cause of acquired nevus of pigmentation is unknown at present, and many nevi are related to external stimulation of the local skin. Hands are often in contact with the outside world, and nevus of pigmented skin can be easily induced by frequent contact with chemicals such as cement, topical medicines such as glucocorticosteroids, exposure to sunlight or trauma.
The left thumb is prone to friction or extrusion due to frequent grasping of objects, and the risk of malignant transformation is relatively high, so it is necessary to go to the hospital for treatment in time.