The sudden growth of brown spots on the soles of the feet may be caused by plantar warts, moles, melanoma and other factors. 1. metatarsal warts: the disease is caused by human papilloma virus infection, usually in the soles of the feet appear flat-like papules or plaques, the color is mostly gray-brown, yellow-brown and so on. The warts may be accompanied by a slight pain when they are pressed. 2. Nevus: This disease may be related to developmental defects, heredity, genetic mutations and other factors, and may appear on the soles of the feet brown, black patches or plaques. 3. Melanoma: this disease is due to the malignant transformation of melanocytes, which is more common on the soles of the feet, usually the original mole rapidly increases in size, bulges, and itches and bleeds and other symptoms. When the soles of the feet suddenly grow brown spots, it is necessary to go to the hospital in time to find out the cause of the disease, and then follow the doctor’s instructions for relevant treatment.