Seasonal affective disorder, also known as winter depression, is an affective, or mood, disorder. Most SAD sufferers experience normal mental health throughout most of the year, but experience depressive symptoms in the winter or summer. The condition in the summer is often referred to as Reverse Seasonal Affective Disorder. Seasonal mood variations are believed to be related to light. SAD is measurably present at latitudes in the Arctic region. Cloud cover may contribute to the negative effects of SAD. SAD can be a serious disorder and may require hospitalization. There is also potential risk of suicide in some patients experiencing SAD