Brown spots (also known as age spots) are small, freckle-like marks that are caused by excessive sun exposure. They commonly appear on the face, chest, shoulders and arms because those areas of the body get the most sunshine. Ultraviolet (UV rays) accelerate the production of melanin, which gives skin its brown pigmentation. Brown spots result from overactive pigment cells and melanin being grouped together in higher concentrations. Melanin tends to develop in small circles in a concentrated area.