Seasonal Affective Disorder (SAD) was first noted before 1845, but was not officially named until the early 1980’s. As sunlight has affected the seasonal activities of animals (i.e., reproductive cycles and hibernation), SAD may occur in humans due to this seasonal light variation. As seasons change there is a shift in our circadian rhythm. This is due partly to the changes in sunlight frequency and duration. The result is having our biological clocks fall out of “step” with our daily schedules. As the days get shorter the problem may worsen.