For the millions of Americans with Seasonal Affective Disorder (SAD), it’s the darkness, not the cold, that makes winter so difficult.

SAD affects at least five percent of Americans. As Reactions host Sophia Cai explains in this video from the American Chemical Society below, the symptoms of SAD are similar to those of garden-variety depression. It’s the timing that’s different; most people’s symptoms set in in late autumn and last through the winter. 

Scientists have yet to pinpoint the exact causes of SAD, but they do have a few ideas. Shorter days mean less sunlight. This may seem like a superficial concern—sure, sunny days make us happier—but the chemistry goes much deeper than that. Exposure to sunlight, or a lack thereof, affects the production and release of important brain chemicals, and any imbalance in these chemicals can make us feel pretty awful.

Fortunately, SAD is very treatable. Talk therapy, medication, and light therapy have all proven helpful. If you’re experiencing symptoms of SAD, give your doctor a call. Winter may be dark, but it doesn’t have to be depressing.

Header image from Reactions.