Brown spots on the calf may be caused by nevus freckle, purpura and post-inflammatory hyperpigmentation, etc. The cause of nevus freckle is not clear. 1. nevus of freckle: nevus of freckle can be seen on the skin or mucous membrane, the patient’s skin lesions are mostly manifested as black-brown spots, the diameter of which usually does not exceed 5mm. the cause of this disease is not yet clear, and it may be related to genetics. 2. allergic purpura: the cause of this disease may be related to infection, heredity and drugs and other factors, the patient’s skin will appear purpura, with the growth of time will change to dark purple or brown, mostly in the limbs, buttocks and other places. 3. Post-inflammatory hyperpigmentation: the causes of this disease include trauma, disease and environmental factors, patients who have suffered from inflammation may appear in the parts of the rash or patches, light brown, dark brown and black. Some patients may develop many brown spots on their calves. The causes of brown spots on the calves are not unique, and it is recommended that patients go to a regular hospital to get a clear picture of the cause of the disease.