Seasonal affective disorder is diagnosed more often in women than men, and it occurs more frequently in younger adults than in older adults. Seasonal affective disorder is more common among people who live far north or south of the equator, perhaps due to decreased sunlight during the winter and longer days during the summer. Other factors that may increase your risk of seasonal affective disorder include a family history of blood relatives with the disorder, or a personal history of major depression or bipolar disorder.
For most people with seasonal affective disorder, symptoms appear during late fall or early winter, and they go away during the sunnier days of spring and summer. Less commonly, people with the opposite pattern have symptoms that begin in spring or summer. In either case, symptoms may start out mild and become more severe as the season progresses.