Hyperpigmentation in the form of melasma, chloasma or age spots can cause light brown spots on the stomach and other areas of the skin, according to Kavi. Some lentigines and melasma spots can be caused by an over-production of melanin while others are sun related.
Solar lentigines, called liver spots or age spots by some, generally form from sun exposure. They appear on the face and hands most often. Melasma or chloasma form from hormonal changes. Melasma is a common skin condition.
Wearing sunscreen and clothing that offers protection from the sun prevents the formation of many types of hyperpigmentation. A dermatologist should check any skin changes for a specific diagnosis.