What Is Seasonal Affective Disorder?

A type of depression that follows seasonal patterns

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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 may also be more likely to experience atypical depressive symptoms, including excessive sleepiness, lethargy, and weight gain.

SAD 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.

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What Is Seasonal Affective Disorder?

SAD used to be considered a unique mood disorder separate from MDD. 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 with SAD has the classic signs and symptoms of clinical depression, but they occur seasonally. In people with SAD, the symptoms follow the same yearly seasonal patterns. 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 mood. Also unlike SAD, people with this more mild condition aren’t considered by the DSM to have a MDD.

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

  • Mood reactivity (mood brightens in response to events)
  • Hypersomnia (excessive sleepiness)
  • Increased appetite, craving for carbohydrates, and weight gain
  • Leaden feelings in the arms and legs
  • Rejection sensitivity

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. Although the specific causes are unknown, seasonal suicides occur more in the spring and early summer than during the autumn and winter months.


Diagnosis of MDD can include a range of tests and scales used to assess 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, accompanied by several other symptoms. These feelings must mark a change from a person's normal state, and the symptoms must also persist for a least two weeks.

To differentiate SAD from MDD, 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 and 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 the circadian rhythm, which is 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 reduced daylight hours.
  • Other scientific evidence has shown that certain personality traits can predispose a person to develop 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 the problems to persist and contribute to feelings of 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 treatment of other types of depression, but with one key difference: bright light therapy. 

Bright Light Therapy

Bright light therapy is a treatment that involves exposure to full-spectrum white light in order to reduce depressive symptoms. Full-spectrum white light differs from ordinary indoor light because it is designed to include the full electromagnetic spectrum and replicate sunshine.

Research shows that exposure to bright light therapy in the morning can reduce symptoms of SAD. Bright light therapy can help alleviate SAD symptoms because it regulates circadian rhythm function through the regulation of melatonin, an important hormone that causes a person to feel sleepy at night when there’s minimal light. 

In summer, sunlight during the 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 in the same way. Light therapy should be used with caution in people who also have bipolar disorder because it has been reported to potentially trigger a manic episode.

Cognitive Behavior Therapy (CBT)

Another treatment that’s been proven effective for SAD is cognitive-behavioral therapy (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.

CBT may also be effective at reducing symptoms of SAD when used as a treatment on its own. One study suggested 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:

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.


Certain lifestyle changes have also been proven beneficial for people who experience SAD.

These include:

  • Exercise: Physical exercise can help by decreasing the body's production of stress hormones, which is believed to improve resilience. 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 help you stay asleep during the night. And keeping technology outside the bedroom can minimize sleep disturbances to help you wake up feeling refreshed.
  • Alcohol and substance abuse: Many people turn to alcohol and recreational drugs when they experience depression. However, the effects of these substances can exacerbate depression and affect your 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 in person or 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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