Melasma is a common problem that causes discoloration and brown patches on the skin.  It is especially common in women, and commonly develops during or after pregnancy, or with hormonal treatments like birth control pills, because female hormones are thought to contribute to melasma development. However, hormones alone are usually not enough to cause melasma.  Sun exposure and sometimes heat exposure combined with hormones make melasma worse and more prevalent.  There is also sometimes a vascular component to melasma where blood vessels near the skin surface make the pigment more noticeable.