When he moved from South Africa to New York City, Norman Rosenthal noticed he felt more depressed during the cold, short days of the city’s winters than he had in his home country.

“It was an illness hiding in plain sight because people said ‘well that’s how everyone feels in winter.’ They didn’t see it as treatable,” says Rosenthal, a psychiatrist at Georgetown Medical School. 

In 1984, he published the first paper to scientifically name the winter blues: Seasonal affective disorder (SAD), also called seasonal depression, was a type of depression brought on by the dark days of winter. 

Subsequent studies have found that this form of depression varies by geography. As much as three percent of the general