Seasonal affective disorder (SAD) is marked by symptoms of depression profound enough to seriously affect work and relationships. The disorder may have its onset in adolescence or early adulthood and, like other forms of depression, occurs more frequently in women than in men. Most people with the "winter blahs" or "cabin fever" do not have SAD. The cause of SAD is not known but is thought to be related to numerous factors such as body temperature, hormone regulation, and ambient light. There is a rare form that occurs in the summer.
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