What Is Seasonal Affective Disorder?

A type of depression that follows seasonal patterns

Seasonal affective disorder (SAD) is a form of major depressive disorder (MDD) influenced by seasonal changes. The majority of people with SAD experience symptoms in the winter, when there’s less daylight, but some people experience an onset of symptoms in the summer.

The main symptoms of SAD are similar to those of MDD, including feelings of excessive sadness, difficulty concentrating, and loss of interest in activities. People with SAD also experience excessive sleepiness, lethargy, and weight gain.

Seasonal affective disorder is diagnosed the same way as MDD, though additional symptoms must also be present. People with SAD are treated with light therapy, psychotherapy, and medications if needed.

It is estimated that between 2% and 5% of the U.S. population is affected by SAD, with symptoms present around 40% of the year.

girl looking out window
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What Is Seasonal Affective Disorder?

Seasonal affective disorder used to be considered a unique mood disorder separate from depression. However, it was reclassified in 2013 by the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM 5), which health professionals use to diagnose mental health disorders.

Today, SAD is considered a specifier for MDD, meaning that a person has the classic signs and symptoms of clinical depression but they occur seasonally. In people with SAD, the symptoms follow the same seasonal patterns yearly. They typically begin in autumn and winter, when daylight hours are shorter, and resolve in spring and summer.  

SAD isn’t the same as the winter blues. Known clinically as subsyndromal seasonal affective disorder (SSAD or sub-SAD), winter blues are a milder form of SAD. SAD causes functional incapacitation that can disrupt daily life, while SSAD primarily affects a person’s mood. Also unlike SAD, people with this more mild condition aren’t considered by the DSM to have depression.

As with any form of MDD, SAD is more than just feeling blue. It is a persistent condition that affects a person’s ability to function normally, disrupting sleep, work, relationships, self-image, and the ability to enjoy things they’ve always enjoyed.


SAD stands out from other depressive illnesses because it’s seasonal. To be diagnosed with SAD, a person must experience symptoms yearly, and they must correspond to seasonal patterns.

The common signs and symptoms of major depressive disorder, which people with SAD also experience, include:

  • Persistent feelings of sadness, anxiety, or emptiness
  • Hopelessness, pessimism, or thoughts of suicide
  • Irritability, guilt, worthlessness, or helplessness
  • Loss of interest or pleasure in hobbies and activities
  • Difficulty concentrating, remembering, or making decisions
  • Insomnia, early awakening, or oversleeping
  • Unexplained fatigue, aches, pains headaches, cramps, or digestive problems

There are some symptoms that are atypical of MDD but common in people with SAD, including:

  • Hypersomnia (excessive sleepiness)
  • Craving for carbohydrates
  • Increased appetite

Severe cases of SAD may require hospitalization.

SAD and Suicide Risk

As with any form of MDD, SAD can increase the risk of alcoholism, substance abuse, and suicidal thoughts. Even so, SAD is not inherently linked to suicide. Seasonal suicides occur more in the spring and early summer than during the autumn and winter months.


Diagnosis for MDD can include a range of tests and scales that assess a person’s depressive symptoms. To be formally diagnosed with clinical depression, a person must demonstrate feelings of sadness, low mood, and loss of interest in usual activities. These feelings must mark a change from someone’s normal state, and they must also persist for a least two weeks. They must also be accompanied by at least five symptoms of depression.

To differentiate SAD from MDD during diagnosis, the following criteria must be met:

  • Depression is present only at a specific time of year (e.g., winter)
  • Full remission occurs at a characteristic time of year (e.g., spring)
  • There have been at least two consecutive episodes of seasonal depression
  • The seasonal episodes of depression must substantially outnumber the non-seasonal ones


Scientists don’t fully understand what causes SAD, but believe it is a multifactorial disorder triggered by intersecting biological, neurochemical, environmental, and psychological factors.

Research suggests that seasonal mood variations are influenced by daylight. The extreme changes in daylight experienced during the seasons can disrupt circadian rhythm, the internal clock that regulates the sleep-wake cycle. This has been demonstrated in multiple studies, where people living at northern latitudes are more likely to have SAD in winter due to minimal daylight hours.

Other scientific evidence has shown that certain personality traits can predispose a person to developing SAD. Specifically, the main personality trait linked to SAD was an avoidance-oriented coping style, in which a person struggles to confront and manage inescapable adversity. People who cope through avoidance deny, minimize, or avoid problems, which can cause them to persist and contribute to distress and depression.

An association between SAD and bipolar disorder has also been demonstrated, and 15% to 22% of people with bipolar disorder have symptoms of seasonal depression. Since mood cycling occurs in both conditions, some scientists believe that SAD is a variant of bipolar disorder.


Treatment for SAD is approached similarly to other types of depression, but with one key difference: bright light therapy. 

Bright Light Therapy

Bright light therapy is a treatment that involves exposing people to full-spectrum white light in order to reduce depressive symptoms. Full-spectrum white light differs from ordinary indoor light because it intentionally includes the full electromagnetic spectrum and replicates sunshine.

Research shows that exposure to bright white light three times a week in the morning can reduce symptoms of seasonal affective disorder. Bright light therapy can help alleviate SAD symptoms because it improves circadian rhythm function through the regulation of melatonin, an important hormone that causes a person to feel sleepy at nighttime, when there’s minimal light. 

In summer, sunlight during daytime naturally suppresses melatonin to help you wake up in the morning and feel alert throughout the day. Bright light therapy has also been shown to increase the production of serotonin, a neurotransmitter that regulates mood.

SAD vs. Bipolar Disorder

Despite the association between bipolar disorder and SAD, these conditions aren’t treated equally. Light therapy should be avoided in people who also have bipolar disorder because it can trigger a manic episode.

Cognitive Behavior Therapy (CBT)

Another treatment that’s been proven effective for SAD is cognitive behavioral therapy, or CBT. This is a type of talk therapy that helps people understand, address, and change negative thought patterns and beliefs.

CBT may be used in tandem with bright light therapy. A six-week study showed that a treatment regimen combining CBT and bright light therapy reduced the intensity of depressive symptoms. Participants in the study also experienced improved remission rates, meaning they were less likely to experience SAD symptoms the following winter.

CBT may also be effective at reducing symptoms of SAD when used as a treatment on its own. Scientific findings suggest that two 90-minute CBT sessions may be as effective as 30 minutes of 10,000 lux light therapy. 


Medications used to treat depression can provide relief to people with SAD. These include selective serotonin reuptake inhibitors (SSRIs), such as:

  • Sertraline (Zoloft)
  • Fluoxetine (Prozac)
  • Paroxetine (Paxil)

Additional medications, including monoamine oxidase inhibitors (MAOIs) and serotonin and norepinephrine reuptake inhibitors (SNRIs), are also prescribed for depression.

Research shows that these medications are especially effective when used in combination with other treatments, such as light therapy. The combined use of light therapy and certain drugs (like SSRIs) are able to achieve rapid improvement of symptoms in some people because it regulates the amount of serotonin available for mood improvement.  


Certain lifestyle changes have also been proven beneficial to people who experience SAD. These include:

  • Exercise: Physical exercise can help people with MDD by decreasing stress hormones, increasing exercise, and improving resilience against challenges. For people with SAD, it’s especially beneficial to exercise outdoors whenever possible since this increases exposure to natural light
  • Schedule changes: Schedule important tasks during peak daylight hours when you are likely to have the most energy
  • Sleep hygiene: When daylight hours are shorter than usual, it’s important to maintain a regular sleep schedule. Blackout shades and eye masks can be used to stay asleep during the night, and keeping technology outside of the bedroom can minimize sleep disturbances so you wake up feeling refreshed
  • Alcohol and substance abuse: Many people turn to alcohol and recreational drugs when they experience depression. However, these symptoms can exacerbate depression and affect sleep, which can further disrupt circadian rhythm. Treatment for alcohol and substance abuse disorders includes medications, support groups, ongoing counseling, and CBT
  • Support groups: Talking with other people who experience SAD can help you feel less alone. SAD support groups can be found on Facebook, Reddit, or other online forums

Where to Seek Help

Treatment and support group referrals can also be found through the SAMHSA National Hotline at 1-800-662-HELP (4357).

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