You’re getting too much sunlight
Sunlight and dark help regulate the natural rhythms of your body—especially melatonin, a hormone the body produces at night. If you’re in the sun all day and then on your phone, tablet, or computer before bed, that extended exposure to bright light could be suppressing the release of this crucial sleep hormone. That’s why one summer SAD theory posits that too much sun disrupts melatonin production, says Derichs.
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You’re not getting regular sleep
Your body’s systems follow a 24-hour series of patterns—your temperature, your metabolism, and your sleep are all dependent on your circadian rhythms, as these patterns are known. “If people stay up later in the summer, it could throw their sensitive circadian rhythms off,” says Derichs. Poor sleep is a risk factor for depression, so if you sleep poorly or significantly less in summer, you could be opening the door to SAD. (Try these tips for getting a sounder, longer full night of shut-eye.)
You live in the South
No one is sure why, says Derichs, but “people in southern U.S. states tend to experience summer SAD more so than those in the north.” Considering that the lower latitudes experience higher temps and warmer nights (which can equal worse sleep), it starts to make sense that the risk may be higher below the Mason-Dixon Line.