As summer fades into fall, the days grow shorter and the weather turns colder, you might also notice a shift in how you feel. You may feel more tired, less motivated or even sad. These feelings are common, but for some, they become stronger and harder to manage. This could be a sign of Seasonal Affective Disorder, or SAD.

We spoke with Tina Baxter, a nurse practitioner at Adult & Child Health. She helped us understand what SAD is and how to tell if your mood changes are temporary or if you might benefit from extra support.

What is SAD?

SAD is a type of depression that occurs during certain seasons. When the season changes again, these symptoms lessen or go away. It usually appears in the fall and winter, though some people can experience SAD in other months as well. It’s more than just feeling “blah” because it’s cold. SAD can affect your mood, energy, sleep and even how you think.

According to Baxter, people experiencing SAD might:

• Feel very tired, even after sleeping
• Stop doing things they usually enjoy
• Feel more irritable or anxious
• Feel hopeless or down most days
• Struggle with concentration
• Crave carbohydrates or notice changes in eating habits
• Have thoughts of not wanting to live
• Experience symptoms for weeks or months

Why does SAD happen?

Experts think SAD is linked to changes in sunlight. Less light can lead to more melatonin in your brain (which makes you sleepy) and less serotonin (which helps regulate mood). Your body’s internal clock can also get thrown off, making it harder to feel energized.

SAD is more common in places with long winters and limited sunlight. Women and adults ages 18 to 30 are at higher risk, and having a family history of SAD can increase your chances.

Baxter notes that if you already live with a mental health condition, seasonal changes can make symptoms worse. “If you’re already an anxious person and it’s wintertime, you might be more anxious,” she says. People with bipolar disorder may also notice more intense mood shifts with seasonal changes.