HARRISBURG, Pa. (WHTM) – Millions of Americans are dealing with seasonal depression, a disorder that can have a major impact on someone’s everyday life.

Experts say it’s common in Pennsylvania, especially during the winter months, but that it’s rarely talked about.

“You can have thought patterns of related to hopelessness and helplessness, [you can also] have thought patterns related to self-harm or thoughts of suicide,” Professor and social worker Dr. John Gallagher said.

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Scientists don’t fully understand what causes Seasonal Affective Disorder, but many believe decreases in serotonin, coupled with winter increases in melatonin, contribute to it.

“Folks who experience depression tend to have lower levels of serotonin, so the lack of sunlight during the fall and through the winter months [contribute to it],” Gallagher said.

Even if feelings of sadness only last a few months, help is available. Light therapy is the most common tool to combat the disorder, though Gallagher said lights you can buy off the internet are rarely effective.

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“But you also don’t want [lights] that are too powerful [because] there seems to be an association with bipolar disorder,” Gallagher. “[And] If light therapy is misused, it can do damage to your eyes into your skin.”

Gallagher also suggested counseling and medication to help treat the disorder, and said it’s best to see someone who specializes in Seasonal Affective Disorder.

“While there are certainly some similarities, treatment approaches for Seasonal Affective Disorder differ from [treatments for] regular depression.”