What is seasonal affective disorder

Seasonal affective disorder is a type of depression that is related to the different seasons. Generally a person with seasonal affective disorder will experience periods of depression that begin and end in a certain season. It is thought to be related to the amount of sunlight a person is exposed to.

The most common type of seasonal affective disorder occurs during the winter months. This is known as winter-onset seasonal affective disorder and is more common in countries that have very short days in winter.


The exact causes of seasonal affective disorder are not clear. It is thought to be associated with a lack of exposure to sunlight during the shorter days of the year. The amount of sunlight that is passed through the eyes to certain regions of the brain directly affects the levels of particular hormones and neurotransmitters in the brain.


The reduced levels of sunlight associated with the winter months can lead to higher-than-normal levels of the hormone melatonin. Melatonin is involved in regulating sleep patterns, and when it is produced in higher amounts, it can lead to sleepiness and decreased energy levels.


Serotonin is a chemical messenger in the body involved in the regulation of mood, appetite and sleep. The production of serotonin is related to the amount of sunlight that passes through the eyes. In the winter months, the limited sunlight results in less serotonin being produced, which may trigger depression.

Circadian rhythm

The body uses sunlight to set its regular biological functions and processes, such as regulation of sleep, appetite, mood and energy. This regulation is known as the circadian rhythm, or biological clock, which usually occurs over a 24-hour cycle. When there is a change in the amount of exposure to sunlight, this rhythm is disrupted and is associated with some of the symptoms of seasonal affective disorder.

Genetic predisposition

Although there is no single gene associated with the onset of seasonal affective disorder, genes are thought to play a role, and people with a family history of depression may be more likely to experience seasonal affective disorder.

Adverse childhood experiences

For some people, experiencing a traumatic childhood event such as abuse or neglect may cause the onset of their seasonal affective disorder.

Summer-onset seasonal affective disorder

Although seasonal affective disorder usually begins during the winter months, some people may experience periods of depression that are associated with the summer months. As well as changes to the circadian rhythm (see above), summer-onset seasonal affective disorder may sometimes be triggered by other factors including:

  • A disruption to routine due to the holiday season;
  • The humidity and heat making normal functioning unpleasant;
  • Body-image issues related to having to wear less clothing during the warmer weather, and;
  • Financial concerns associated with family holidays.


A unit of inheritance (heredity) of a living organism. A segment of genetic material, typically DNA, that specifies the structure of a protein or related molecules. Genes are passed on to offspring so that traits are inherited, making you who you are and what you look like.


A chemical substance secreted in one part of an organism and transported to another part of that organism, where it has a specific effect.


A chemical messenger within the brain that is thought to play a role in mood and behavior. Many antidepressant medications act by increasing the amount of serotonin in the brain.


A chemical produced by the pineal gland in the brain that prepares the body for sleep. It is also available as a medication to help treat sleeping disorders.

Risk factors

Factors that may increase a person's chance of developing seasonal affective disorder include:

  • Being female;
  • Being a young adult;
  • Having a family history of depression;
  • Having bipolar disorder or clinical depression, and;
  • Living far from the equator (for winter-onset seasonal affective disorder).

Signs and symptoms

The main symptom of seasonal affective disorder is a period of depression that begins and ends during a specific season every year, usually autumn or winter (winter onset), but occasionally spring or summer (summer onset). Usually a person with seasonal affective disorder will not experience any symptoms beyond the problematic season.

During a period of depression, a person with seasonal affective disorder may experience a range of behavioral and physical symptoms, or have certain thoughts and feelings:

Behavioral symptoms

A person with seasonal affective disorder may be likely to:

  • Want to stay at home, rather than go out;
  • Stop doing usually enjoyable activities;
  • Withdraw from family and friends;
  • Have trouble concentrating;
  • Not get much done at work or school, and;
  • Experience irritability or agitation.

Physical symptoms

Physical symptoms may include:

  • Extreme tiredness;
  • Difficulty sleeping, or sleeping too much;
  • Change in weight;
  • Change in appetite, and;
  • Headaches and muscle pains.

Thoughts and feelings

During periods of depression, a person with seasonal affective disorder may feel like they are a failure, or that life is not worth living. They may also lack confidence, have difficulty making decisions, experience feelings of disappointment or feel overwhelmed.

For some people these feelings may be mild, while in others they may be very severe and cause a person to have trouble carrying out everyday tasks.

Methods for diagnosis

To diagnose seasonal affective disorder, a doctor may ask a person about their medical history and the type, onset and duration of symptoms. In some cases a doctor may order some laboratory tests.

Seasonal affective disorder may be diagnosed when:

  • Symptoms begin and end during a specific season every year;
  • Symptoms have occurred for a minimum of two years, and;
  • No symptoms are experienced beyond the problematic season.

Types of treatment

There are several ways to treat seasonal affective disorder. Treatment may involve a combination of light therapy, medication, psychotherapy and self-care treatments.

Light therapy

Light therapy, or phototherapy, involves exposing a person to a very bright light, typically from a special fluorescent lamp, for 30-90 minutes a day during winter. This is usually done early in the morning, to mimic sunrise.

The intensity of light treatment depends on the power of the light source being used and how far it is placed from the person. This is expressed in a unit of measure of illumination called lux. The light used in light therapy is typically in the order of 10,000 lux, which is around 10 times brighter than sunlight an hour before sunset. At the intensity of 10,000 lux, spending just 15 minutes in front of the light provides the exposure equivalent of two hours outside in the sun.

Light therapy is not suitable for people with particular eye diseases such as macular degeneration or retinitis pigmentosa, or who are taking medication that increases their sensitivity to light.

Although not common, some people may experience side effects from light therapy such as eye strain, headache, irritability, fatigue and insomnia.


Psychotherapy is sometimes referred to a 'talking therapy' and describes the process of treating a mental health condition by helping a person to understand their condition and manage their symptoms. If someone has depression, meeting regularly with a therapist to discuss their thoughts and feelings, and any problems they may be having, may help them manage their condition.

Psychotherapy, or 'talking therapy', may help with the management of seasonal affective disorder. 


Antidepressant medication may be prescribed to people with more severe forms of seasonal affective disorder, or for those for whom light therapy is ineffective. Antidepressants help to control mood by restoring the balance of chemicals in the brain, such as serotonin and dopamine.

Antidepressant medications generally need to be taken for at least two weeks before any improvement in symptoms is seen. Medication may also need to be continued for a time even after the symptoms have gone, to prevent them from coming back. When stopping antidepressant medication, the dose usually needs to be reduced gradually over time, in consultation with a doctor, to prevent any withdrawal responses.

Side effects

As with most medications, some people may experience side effects when taking antidepressants. Some common side effects include nausea, dizziness, tiredness and sexual dysfunction. Some antidepressants can have more serious side effects if they are taken with certain other medications or herbal remedies, or when combined with alcohol. A person's doctor will work with them to find the medication that is best for them.

Very rarely, some antidepressants may increase suicidal thoughts and the risk of suicide. The risk is highest in the first week after starting antidepressant treatment, or when the dose of the antidepressant is changed. If someone experiences suicidal thoughts, it is important to contact a doctor immediately.

Self care

Simple things that can be done at home to help manage seasonal affective disorder include:

  • Increasing general exposure to sunlight by taking long walks outside during the daylight hours (for winter-onset seasonal affective disorder);
  • Getting early-morning sunlight, which effectively shifts the body clock forward for summer-onset seasonal affective disorder;
  • Adjusting work or a home office to be closer to a natural source of sunlight;
  • Maintaining good sleep patterns;
  • Eating a balanced diet;
  • Regular exercise, and;
  • Avoiding alcohol and other drugs, which may worsen depression.


A chemical messenger that acts as a neurotransmitter in the brain and a hormone outside the central nervous system. In the brain, dopamine plays a role in motor control and reward-motivated behavior. Outside the brain, dopamine acts across several parts of the body as a local chemical messenger.


A state of exhaustion and weakness.

Retinitis pigmentosa

A group of diseases in which the retina degenerates, leading to vision loss.


A chemical messenger within the brain that is thought to play a role in mood and behavior. Many antidepressant medications act by increasing the amount of serotonin in the brain.

Potential complications

If it is left untreated, the symptoms of seasonal affective disorder may become severe, with extreme cases having a risk of suicide. Other potential complications include:

  • Substance abuse;
  • Social withdrawal, and;
  • Impaired school or work performance.


With treatment, the outlook for people with seasonal affective disorder is generally good. Most people eventually get better and return to their normal daily activities. However, recognizing the signs and getting treatment early may help them get better sooner. Some people may need ongoing treatment, as their condition may return with the problematic season.


Although there are no clear ways of preventing seasonal affective disorder, individuals who are prone to it may benefit from the following measures:

  • Beginning light therapy before the onset of winter months;
  • Spending time outside every day, even if it is cloudy (for summer-onset cases, spending time outside in the early mornings);
  • Eating a well-balanced diet;
  • Exercising regularly, and;
  • Avoiding social withdrawal.

Support services

If you or someone you know needs help, please call or visit:

Support Groups - Online Support Groups Call 1-800-273-TALK or Text MHA to 741741

National Suicide Prevention Lifeline Lifeline Call 1-800-273-8255

The Lifeline provides 24/7, free and confidential support for people in distress, prevention and crisis resources for you or your loved ones, and best practices for professionals.

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