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Seasonal affective disorder (SAD) is a type of depression that comes and goes in a seasonal pattern.
SAD is sometimes known as "winter depression" because the symptoms are more apparent and tend to be more severe during the winter.
The symptoms often begin in the autumn as the days start getting shorter. They're typically most severe during December, January and February.
SAD often improves and disappears in the spring and summer, although it may return each autumn and winter in a repetitive pattern.
Symptoms of SAD can include:
For some people, these symptoms can be severe and have a significant impact on their day-to-day activities.
Read more about the symptoms of SAD.
You should consider seeing your GP if you think you might have SAD and you're struggling to cope.
Your GP can carry out an assessment to check your mental health. They may ask you about your mood, lifestyle, eating habits and sleeping patterns, plus any seasonal changes in your thoughts and behaviour.
Read more about diagnosing SAD.
The exact cause of SAD isn't fully understood, but it's often linked to reduced exposure to sunlight during the shorter autumn and winter days.
The main theory is that a lack of sunlight might stop a part of the brain called the hypothalamus working properly, which may affect the:
It's also possible that some people are more vulnerable to SAD as a result of their genes, as some cases appear to run in families.
A range of treatments are available for SAD. Your GP will recommend the most suitable treatment programme for you.
The main treatments are:
Read more about how seasonal affective disorder is treated.