Hyperpigmentation is caused by the body producing too much melanin, or pigment. They can take years to show up on the skin though, so you won't always know when it's happened to you. Hyperpigmentation may also result from acne, certain drugs, topical skin treatments and other skin conditions.
Age spots (sometimes called sun spots) appear at random, in patches or scattered and aren't usually symmetrical. They are caused by sun exposure and can respond to a range of treatments.
Melasma is a chronic skin disorder that results in symmetrical, blotchy, brownish facial pigmentation. It can lead to considerable embarrassment and distress.