Black spots growing on the skin may be caused by sunburn, nevus melanoma, acanthosis nigricans and other diseases. 1. Sunburn: i.e. solar dermatitis, if you are usually exposed to the sun for a long time, this will make the ultraviolet rays damage the local skin and stimulate the melanocytes to secrete a large number of melanin particles, which will make the black spots grow on the skin symptoms. 2. Melanotic nevus: when suffering from melanotic nevus, it will also make black spots grow on the skin, which is mainly caused by the melanocytes staying on the skin surface when they move from the neural crest to the surface skin during the embryonic development period. It also has a certain relationship with hormone level, immunosuppression, and heredity. 3. Acanthosis nigricans: If the patient’s body type is too obese, or the body’s androgen secretion is more vigorous, this will promote the local melanocyte enhancement, which will cause the situation of black spots on the skin. When black spots on the skin may also be related to other diseases, it is recommended to go to the regular hospital in time, after a clear diagnosis by a specialist, early targeted formal treatment.