Do you notice changes to your mood during the winter? If so, you could be prone to seasonal affective disorder, or SAD, a kind of depression that ebbs and flows with the year. The condition is also sometimes called “winter depression” because it usually, though not always, occurs during the cold and dark of winter.

According to Mental Health America, about 5% of people in the U.S. have seasonal depression. Women are far more likely to experience it than men — four out of five people who have SAD are women. Geography also plays a role in your risk of SAD. Fewer people have the condition in the south, closer to the equator.

Although the symptoms of SAD last only a season, it’s important to take it seriously.

“The most common misconception is that it is ‘just’ winter blues and not that big of a deal,” Dr. Jeff Temple, a licensed psychologist and professor at the University of Texas Medical Branch, told Fortune. “On the contrary, it impacts millions of Americans with symptoms consistent with major depression.”

Know the Symptoms

Ranging from mild to severe, SAD symptoms look a lot like standard clinical depression, only with a seasonal regularity. Some common symptoms include:

• Low mood and energy for long periods of time
• Fatigue and lethargy
• Changes in sleep
• Weight changes
• Anger and irritability
• Difficulty concentrating
• Loss of interest in things you typically enjoy
• Having a hard time getting out of bed in the morning
• Feelings of despair, hopelessness, or worthlessness
• Food cravings or changes in eating habits

For most people, these cyclical symptoms are manageable with certain coping tools. For others, the symptoms can get so severe that they interfere with everyday life and activities.

So, what exactly causes SAD?

Researchers don’t fully understand what causes SAD, although light appears to play a role. The reduced amount of daylight in winter may affect serotonin levels in some people. Serotonin is the chemical in the brain that regulates your mood. Lower levels of it have been associated with depression.

Melatonin, a hormone that regulates sleep, may also contribute to SAD. Winter’s long hours of darkness may trigger the production of higher-than-normal amounts of melatonin in some people, much as it does for animals that hibernate. Extra melatonin could help explain the low energy and sleep changes common in SAD.

How to treat it

If you’re diagnosed with seasonal affective disorder, there are several treatment options available, including:

• Lifestyle changes. Try to get outside and expose yourself to as much natural light as possible throughout the day. Be sure to exercise, eat a healthy diet, and manage stress levels.
• Light therapy. This treatment, also called phototherapy, involves spending about 30 minutes in the morning in front of a lightbox, a special lamp that simulates natural daylight.
• Talk therapy. Counseling can help you manage stress levels during periods of SAD and is often suggested in combination with a lightbox.
• Antidepressants. If other options aren’t working, your doctor might prescribe antidepressants to help relieve the symptoms of depression.

If you feel you might be suffering from seasonal affective disorder, don’t hesitate to call your doctor to discuss the best treatment option for you.