Seasonal affective disorder (SAD) is a form of depression that people experience at a particular time of year or during a particular season. It is a recognised mental health disorder.

Most of us are affected by the change in seasons – it is normal to feel more cheerful and energetic when the sun is shining and the days are longer, or to find that you eat more or sleep longer in winter.

However, if you experience SAD, the change in seasons will have a much greater effect on your mood and energy levels, and lead to symptoms of depression that may have a significant impact on your day-to-day life.

Most people experience SAD during the winter. Less commonly, some people find they experience SAD in reverse – with depressive symptoms occurring in summer.

SAD is most common in countries like the UK where there are large changes in the weather and daylight hours in the different seasons.

It's like having your own portable black cloud.

SAD can also worsen symptoms of existing depression that you experience throughout the year.

This information was published in June 2016. We will revise it in 2019.