There are several different kinds of pigmented regions:
Small, darkened patches of skin (called either liver or age spots) are pigment spots on your face, arms, and hands that are usually caused by sun exposure.
Hormones from birth control pills and pregnancy can cause melasma or chloasma. This type of pigmented region affects around 90% of pregnant women and results in dark, large, and irregularly shaped areas on your arms, face, and sometimes on other areas of the body.
This type of pigmented region occurs when a skin trauma or injury heals and leaves a flat area of discoloration. This is commonly caused by acne. Birthmarks, scarring, skin cancers, and solar or actinic keratoses also cause patches of skin to become darker.