Dark spots, also known as age or sun spots, are tan to brown 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 that can get the most sun. Ultraviolet (UV rays) accelerate the production of melanin, which gives skin its brown pigmentation.
Sun spots result from overactive pigment cells and melanin being grouped together in higher concentrations. Excessive sun exposure is a direct cause of dark spots.