When winter comes a-knocking, many individuals report feeling a little blue. It’s no surprise; the lack of sunlight common to the colder months has been linked to increased feelings of sadness and exhaustion in most people. But for some, the colder weather brings more than just a case of the winter blues. In fact, according to American Family Physician, about 5 percent of adults in the U.S. experience SAD and it typically lasts about 40 percent of the year. It is more common among women than men.

What is SAD?  Kelly Rohan, Ph.D., a psychologist at the University of Vermont, says that, first and foremost, SAD is a form of clinical depression. “Many think that SAD is just something mild, just a matter of the winter blues or not liking winter,” she says. “But it’s much more than that. You have the typical symptoms of depression but they follow a seasonal pattern. Most commonly, SAD symptoms occur in the fall and in the winter and then fully resolve by spring and summer, though a very small minority of individuals show the opposite pattern.”

Typical symptoms are in line with what you see in other types of depression, including low energy, difficulty concentrating, sleep disruptions, eating disturbances, sadness, and anhedonia. But individuals with SAD often tend to sleep too much and increase their eating, especially carbohydrate-rich foods, which often leads to significant weight gain. And while SAD-related symptoms tend to resolve with the coming of warmer weather, it is a recurring condition. Most patients experience SAD-related depression from year to year, though its severity may vary.

To date, clinicians don’t understand what causes SAD—but winter’s short days are its reliable trigger. As the days grow shorter, symptoms get worse. Rohan suggests that any individuals who are experiencing symptoms that are interfering with their life in a significant way see a qualified medical health professional immediately for proper diagnosis. Once diagnosed, clinicians can offer several ways to help to get your SAD under control.

“The good news is there are a number of effective treatment options out there. Light therapy, or the daily exposure to a special bright artificial light has been shown to help. And antidepressant medication and cognitive behavioral talk therapy are also evidence-based therapies that are effective in reducing symptoms,” Rohan says. “Your clinician should talk to you on an individual basis about the pros and cons of each—and arrive at a treatment plan that will work for you. Because SAD is a recurring condition, you need to have a long-term perspective when choosing treatment.”

But Rohan is adamant that individuals should never try to self-diagnose or self-treat SAD. “I’ve probably talked to hundreds of different people who have had SAD over the years. And it often takes them years to even recognize their pattern of depression,” she says. “This can be a very severe disorder. And you need the help of a qualified mental health professional to help you deal with it.”