This may be due to brown spots which are dark patches are associated with aging and sun damage. They are located in areas most often exposed to the sun such as the hands, face, forehead, head, arms and shoulders.
Pigmentation may be due to melasma which is pigmentation usually associated with hormonal factors such as pregnancy, contraceptive pills and the menopause. The dark patches often develop on the cheeks, forehead and upper lip.
Another cause of pigmentation is post inflammatory pigmentation which is caused by acne, rashes, scratch marks or injury to the skin.