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Seasonal Affective Disorder (SAD)

By Olivia Guy-Evans, published March 08, 2022

by Saul Mcleod, PhD

Seasonal Affective Disorder (SAD) is categorised as a mood disorder which results in feelings of depression, normally brought upon by changes in the seasons.

SAD is a condition that begins and ends at around the same time every year for people who suffer from this, which makes it different from other mood disorders.

The majority of individuals with SAD experience symptoms in the winter months, making them feel lower in mood and lacking in energy. In rare cases, another form of seasonal depression can occur in the spring and summer months, which can result in irritableness and difficulty sleeping.

The symptoms of SAD can be distressing and overwhelming and could even interfere with daily functioning.

SAD is most common in countries in northern climates, affecting approximately 6% of the population of the United States and 3% of the United Kingdom for instance.

The onset of SAD can begin at any age but typically the first instance is noticeable between the ages of 18 and 30 years old.

Symptoms of SAD

Some of the general symptoms of SAD may include:

  • Feeling depressed most of the day

  • Feeling depressed most days

  • Low in energy

  • Problems sleeping

  • Changes in appetite or weight

  • Agitation 

  • Difficulty thinking, concentrating, or making decisions

  • Feeling worthless or guilty

  • Suicidal thoughts

Winter SAD is the most common and recognisable type of SAD and usually is associated with the normal warning signs of depression. This will usually begin in late fall or early winter.

Below are some of the symptoms associated with winter-specific SAD:

  • Low in energy or fatigued

  • Sleeping too much

  • Eating too much

  • Weight gain

  • Feeling sad or hopeless

  • Irritability 

  • Lack of interest in social activities 

  • Reduced sexual interest

  • Thoughts of suicide

A rarer case of SAD is summer-onset SAD, often called summer depression. This will usually occur in the spring or early summer. Below are some of the symptoms associated with summer-specific SAD:

  • Feeling agitated

  • Difficulties sleeping – insomnia

  • Lack of appetite

  • Losing weight

  • Feeling anxious

As a result of the symptoms of SAD, further complications could occur such as the onset of another mental health condition such as generalised anxiety or bipolar disorder, if gone untreated.

Likewise, social anxiety may become prevalent since many people with SAD may wish to socially withdraw when they are experiencing down moods.

This could result in losing social support networks or finding it harder to socialise again once the seasonal depression has ended. Another complication to discuss is that those with SAD may abuse substances like alcohol and drugs as a way of coping with their symptoms.

This can ultimately lead to a dependence on these substances and lead to further mental health and physical health issues. In the most severe cases, if left untreated, SAD could result in suicidal thoughts or self-harming behaviours. 


The precise cause of SAD is unknown, and factors may vary from person to person. However, there are some explanations for why certain people experience this condition. 

A risk factor for developing SAD could be due to geographical location. Those who live in countries which do not have a lot of sunlight, are more at risk of developing SAD than those who live in countries with more sunlight.

This will usually be countries which are furthest away from the equator such as Canada and Iceland for instance. These countries tend to have longer hours of darkness during the winter months as well as longer days of sunlight during the summer. These inconsistencies in the seasons may be a strong cause for the onset of SAD. 

Similarly, due to reduced levels of sunlight in winter, this can disrupt the body’s internal biological clock which regulates hormones, sleep, and mood. This can result in more depressed feelings as a result.

One hormone, which works as a neurotransmitter in the brain is serotonin. Serotonin plays a key role in mood and is associated with other mood disorders.

Reduced sunlight can cause a decrease in serotonin being produced in the brain. If there is not enough serotonin circulating around the brain, this can lead to lower moods and fatigue.

Another hormone is melatonin which plays an important role in mood and sleep patterns. Changes in the seasons can disrupt the balance of the body’s levels of melatonin and thus can be a cause for feelings of sadness and sleep problems. 

A study in 2014 investigated some of the characteristics that may be associated in individuals who have SAD. It was found that females were significantly more likely than men to experience SAD, which tends to be a common finding for this condition.

Likewise, the researchers found that those who score higher on the neuroticism scale for personality were more likely to report symptoms of SAD (Oginska and Oginska-Bruchal, 2014). 


The Diagnostic Statistical Manual of Mental Disorders (DSM-IV) describes SAD as not a separate condition from depression, but as a type of this – major depressive disorder with seasonal pattern.

SAD is mainly characterised by a seasonal pattern of depressive recurrences over the years. 

To meet the criteria of SAD, the depression should only be present at a specific time of the year. For most people this is usually in the late fall or early winter months but can be at the end of spring or start of summer in rarer cases.

Full remission must happen at a characteristic time of year as well to meet the criteria, e.g. remission occurring in the early spring. 

An individual should demonstrate at least two episodes of depressive disturbance in the previous two years.

Seasonal episodes of depression should also substantially outnumber nonseasonal episodes of depression. Meaning that the depression should be seasonally specific as depressed episodes experienced all year round would probably qualify for major depressive disorder on its own, rather than SAD.

Individuals who meet the criteria for SAD may be more likely to report atypical symptoms alongside the typical symptoms of depression. These atypical symptoms may include hypersomnia, increased appetite, and a craving for carbohydrates. 

At least five symptoms of depression must be present during the same two-week period, nearly every day, and representing a change from normal behaviours.

At least one of the symptoms being experienced to meet the DSM-IV criteria must be either a depressed mood or a loss of interest or pleasure.

The symptoms being experienced must also not be accounted for by other medical conditions, substance-use, another mood disorder, or a bereavement.

These symptoms also should not be explained by a psychotic disorder such as schizophrenia. 

Treatment and prevention 

Whilst symptoms of SAD will generally improve on their own with the changing of the seasons, these symptoms can be improved quicker with treatments.

Some of the treatments will be the same for depression in general. Due to the predictability of when SAD will occur, can make it easier to know when to begin treatments. 

Light therapy is a common treatment for SAD. This involves sitting in front of a light therapy box which emits a bright light, filtering out harmful UV rays.

The aim of this is to try to mimic the sunlight that is not as prevalent in the winter months. This treatment is linked with the melatonin theory of why SAD symptoms may occur in winter. As sunlight can affect the biological clock, the use of light therapy should help to restore balance of melatonin and increase mood.

The amount of time spent in front of the light box can vary, but it is usually recommended to sit in front of it for about 20 minutes a day, in the morning during the winter months. 

Most people report some improvements to mood within a couple of weeks of regular use of light therapy. It can also be used as a prevention of the onset of SAD symptoms.

If someone anticipates that their SAD symptoms return in the late fall for instance, they could start using the light box in earl fall to help prevent symptoms.

Light therapy is a non-pharmacological treatment as is generally safe to use. Some of the research into the effectiveness of light therapy is limited with small sample sizes and it may not be a suitable treatment for those experiencing severe symptoms such as suicidal thoughts, but it can be used at individual’s discretion.  

Alternatively, the use of antidepressants, specifically selective serotonin reuptake inhibitors (SSRIs), which are used to treat depression, can also be an effective treatment for SAD.

SSRIs affect the neurotransmitter serotonin in the brain through blocking the reuptake of serotonin back into the neuron which releases it.

With more serotonin circulating between the neurons, this makes it more likely that the serotonin will reach the next neuron and have more of an effect on the brain and mood.

SSRIs are widely used and accepted as an effective treatment for symptoms of depression, although it may not be recommended to continue use once the season of depression is over.

SSRIs require a gradual withdrawal, decreasing the dose over time. This can make it difficult to stop once the winter is over, and thus needs to be taken into consideration if beginning this treatment. 

Psychotherapies are also proven to be a useful treatment for depression and specifically for SAD. Cognitive behavioural therapy (CBT) is a popular type of psychotherapy which involves working with a therapist to talk through unhealthy behaviours and thoughts which come as a result of depression.

Together with the therapist, problems can be solved in order to alter the thinking and behaviours of the individual into more healthy and realistic ones. 

Aside from treatments, there are some preventative measures that can be taken to help stop or limit the severity of the symptoms of SAD.

Taking some time to be outside, even if there is little sunlight, or sitting near a window in the home, can help with improving mood. Similarly, taking care of general health such as eating well and regular exercise, especially near the predicted onset of SAD, could help with improving symptoms.

Finally, keeping a good social network, meeting friends and family, or participating in group activities should also help.

Do you need mental health help?


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Contact the Samaritans for support and assistance from a trained counselor:; email [email protected].

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About the Author

Olivia Guy-Evans obtained her undergraduate degree in Educational Psychology at Edge Hill University in 2015. She then received her master’s degree in Psychology of Education from the University of Bristol in 2019. Olivia has been working as a support worker for adults with learning disabilities in Bristol for the last four years.

How to reference this article:

Guy-Evans, O. (2022, March 08). Seasonal affective disorder (SAD). Simply Psychology.


Fulghum Bruce, D. (2020, September 12). Seasonal Depression (Seasonal Affective Disorder). WebMD.

Mayo Clinic. (2017, October 25). Seasonal affective disorder (SAD).

Roth, E. (2020, June, 29). Seasonal Affective Disorder (Major Depressive Disorder with Seasonal Pattern). Healthline.

Saeed, S. A., & Bruce, T. J. (1998). Seasonal affective disorders. American family physician, 57(6), 1340.

Oginska, H., & Oginska-Bruchal, K. (2014). Chronotype and personality factors of predisposition to seasonal affective disorder. Chronobiology international, 31(4), 523-531.

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