Seasonal affective disorder also called winter depression, winter blues or the hibernation reaction is a type of depression that arises as the days become shorter in the winter. Seasonal affective disorder (SAD) is said to grow from insufficient bright light during the winter months which is natural. It has been proved that bright light in the winter or the fall months tend to alter the chemicals in some people's brains. SAD is mostly found in people who live in places that are away from the equator. Seasonal affective disorder can occur in people of any age and is found more in women than men. However, researchers are still searching to find the exact reason about how this occurs and the details behind this disorder.

SAD symptoms are different in different seasons. In winter, the symptoms are usually tiredness, fatigue, depression, crying spells, irritability, trouble concentrating, body aches, loss of sex drive, poor sleep, decreased activity level, and weight gain. While in summer, the symptoms include insomnia, poor appetite, weight loss, irritability, difficulty concentrating, and crying spells. Sometimes seasonal affective disorder can also bring thoughts of suicide in minds of the patient. There is a treatment that is given to people who are suffering from seasonal affective disorder, and it is called light therapy.

Light therapy, also known as phototherapy, involves light boxes which are kept in use for approximately 30 minutes every day in the morning and evening for best results. Light therapy also involves some side effects, but is the best way to treat seasonal affective disorder. The side effects of light therapy include insomnia, headaches and eyestrains. Apart from using these light boxes the other way in which seasonal therapy disorder can be cured is by using some class of medications like fluoxetine, sertraline, paroxetine and citalopram. These medications also come with some side-effects that include insomnia, nausea, diarrhea, decrease in sex drive, etc. Physiotherapy can also be counted as one of the cures of seasonal affective disorder. For pregnant women who suffer for seasonal affective disorder, medications should be used with particular care. For them, it is prescribed to use acupuncture as a cure.