As many as 6 of every 100 people in the United States may have winter depression. Another 10% to 20% may experience mild SAD. SAD is more common in women than in men. Although some children and teenagers get SAD, it usually doesn't start in people younger than 20 years of age. For adults, the risk of SAD decreases as they get older. SAD is more common in northern geographic regions.

Although your symptoms are clues to the diagnosis, not everyone with SAD has the same symptoms. Common symptoms of winter depression include the following:

• A change in appetite, especially a craving for sweet or starchy foods
• Weight gain
• A heavy feeling in the arms or legs
• A drop in energy level
• Fatigue
• A tendency to oversleep
• Difficulty concentrating
• Irritability
• Increased sensitivity to social rejection
• Avoidance of social situations

Symptoms of summer depression include poor appetite, weight loss and insomnia. Either type of SAD may also include some of the symptoms that are present in other forms of depression. These symptoms include feelings of guilt, a loss of interest or pleasure in activities you used to enjoy, ongoing feelings of hopelessness, and physical problems, such as headaches.

When used properly, light therapy seems to have very few side effects. Side effects may include eyestrain, headache, fatigue, irritability and inability to sleep (if light therapy is used too late in the day). For people who have manic depressive disorders, skin that is sensitive to light, or medical conditions that make their eyes vulnerable to light damage, light therapy should be used with caution.

Tanning beds shouldn't be used to treat SAD. The light sources in tanning beds are high in ultraviolet (UV) rays, which harm both your eyes and your skin.