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Depression, part 1: Symptoms, types, and causes

Reviewed by Stephanie Steinman, PhD, CSAC

A woman leans against a wall and stares into the distance

What is depression? 

Depression is often described as the world’s most common mental health disorder. It manifests in feelings of sadness, loneliness, emptiness, and hopelessness that interfere with your daily life. It can impact your work, your relationships, your energy, and your ability to function. 

Globally, depression affects approximately 280 million people.1 According to the US Department of Health and Human Services, nearly 8% of American adults and 16% of children ages 12 to 17 had at least one major depressive episode in 2019.2 Those numbers increased in 2020 during the coronavirus pandemic.3 

Depression vs. sadness 

We feel sadness after loss, disappointment, and other life challenges. Sad feelings are typically transient, meaning they resolve themselves over time. Many of us find some relief from sadness in positive experiences: encouraging words from a friend or time spent with loved ones. 

Depression, meanwhile, is a persistent, longer-lasting state that changes the way you live. It’s hard to interrupt depression without professional help. 

If you’re overwhelmingly sad for longer than two weeks, you may be depressed. With depression you may also feel apathetic, empty, hopeless, or uninterested in things you once enjoyed—or you may feel like a “fog” is clouding your life. 

Depression vs. grief 

Grief is a natural response to loss, death, or unexpected change. It shares many symptoms with depression, and you can experience both grief and depression at once. Sometimes grief triggers depression—and people with depression may experience grief after a loss. 

Despite their similarities, grief and depression are different mental states. A specific event, like a death or other loss, triggers grief. Grief’s symptoms usually dissipate over time but can resurface in certain situations, like anniversaries or holidays. 

Depression, on the other hand, may or may not be triggered by a specific event or circumstance. Depression’s symptoms are unrelenting and don’t usually improve over time without treatment. Treatment can help grief resolve more quickly, but treatment is typically necessary for depression to resolve at all. 

Depression vs. anxiety 

Depression and anxiety are two separate mental health disorders, though you can experience both at once. In anxiety disorders, excessive worry impacts your life, while depression generally involves feelings of emptiness and hopelessness. 

Signs and symptoms of depression 

Depression can show up differently in different people, and you may experience different symptoms depending on the type of depression you have. 

Common signs of depression include: 

  • Feelings of sadness, loneliness, emptiness, or hopelessness 
  • Loss of interest in activities that previously brought happiness, pleasure, or joy 
  • Low energy or constant fatigue 
  • Difficulty sleeping (insomnia), or oversleeping (hypersomnia) 
  • Loss of appetite, resulting in weight loss; or overeating, resulting in weight gain
  • Decreased sexual desire 
  • Unexplained physical pain 
  • Difficulty concentrating or remembering 
  • Feelings of irritability or frustration 
  • Trouble with decision-making 
  • Feelings of anxiety or restlessness 
  • Thoughts of guilt, worthlessness, or death 
  • Thoughts of suicide 

If you’ve had one or more of the above symptoms for at least two weeks, you may want to seek professional help for depression. 

According to the Substance Abuse and Mental Health Services Administration (SAMHSA), a person has had a major depressive episode (MDE) if they’ve felt depressed for at least two weeks and have also struggled with “sleeping, eating, energy, concentration, self-worth,” or repeated thoughts of death or suicide.4 

If you’re in crisis or having thoughts about suicide, please call the 988 Suicide & Crisis Lifeline for free, confidential support 24 hours a day, 7 days a week: 988 or 1-800-273-TALK (8255)

Types of depression 

Depression comes in many different forms, ranging in duration and severity. It can also look different if you have it along with another mental health disorder, such as obsessive-compulsive disorder (OCD) or bipolar disorder.  

Common types of depression include: 

  • Major depressive disorder (MDD): Also called “clinical depression,” MDD is one of the more serious forms of depression. It usually occurs as an episode that lasts weeks, months, or years. 
  • Persistent depressive disorder (PDD): Formerly called “chronic major depression” or “dysthymia,” PDD is considered more moderate symptomatically, but it lasts longer than MDD. To be diagnosed with it, you must have depressive symptoms for at least two years. 
  • Psychotic depression: This severe form of depression combines MDD and psychosis (for example, hallucinations or delusions). It often requires hospitalization. 
  • Postpartum depression: New parents may go through postpartum depression (sometimes called “postpartum blues” or “baby blues”) after their baby arrives. It’s usually associated with biological mothers, but biological fathers and adoptive parents can have it too. 
  • Seasonal affective disorder (SAD): Seasonal change can cause depression. Seasonal affective disorder usually occurs during colder, darker seasons like fall and winter, with symptoms easing in spring and summer. 

How does depression progress? 

Major depressive disorder, also knowns as clinical depression, is categorized in one of three stages: mild, moderate, or severe. This continuum doesn’t move in a straight line—you don’t need to have had mild depression first to be diagnosed with a moderate form, for instance. Everyone’s different, which means the way you experience depression may vary from others. 

  • Mild depression may not sound too severe, but it’s still serious enough to interfere with your daily life. You may notice a loss of interest in your favorite activities or a general feeling of hopelessness. It may be difficult to eat or sleep. You may be irritable or fatigued; you might have unexplained physical pain or struggle with decision-making.
  • Moderate depression, like mild depression, affects your daily functioning—but in addition to affecting your personal life, it impacts you in other ways. Your performance at work may noticeably slip, or you may forget school assignments. Friends and family may notice a change in your behavior and express concern. 
  • Severe depression is the most serious form of depression. You may find it nearly impossible just to get out of bed in the morning. You may struggle with suicidal thoughts and find it hard to take care of yourself. Severe depression can sometimes be accompanied by other mental health problems, like psychosis.

Causes of depression 

There’s no single or universal cause of depression, but certain factors can increase your risk: 

  • Biochemistry: The ways our brains develop and work affect our experience of the world. Generally speaking, chemical imbalances in the brain seem to be related to depression. Additionally, certain hormones can affect your risk. 
  • Genetics: If a relative has been diagnosed with depression or another mental health condition, you may be at increased risk. 
  • Trauma: Abuse, loss, suffering, and other forms of trauma may trigger a depressive episode. 
  • Illness: Struggling with a chronic disease or disorder can increase your risk for depression. This includes physical illnesses, such as cancer, as well as other mental health disorders, like PTSD. 
  • Medications: Certain medications—including beta blockers, corticosteroids, and benzodiazepines—may trigger or worsen depressive symptoms. 
  • Substance abuse: Alcohol or drug abuse can increase your risk. One study found that nearly 64% of people who were dependent on alcohol also had depression.5 
  • Lack of identity support: According to the American Psychiatric Association (APA), people who identify as LGBTQIA+ are 2.5 times more likely to experience depression than people who identify exclusively as heterosexual. Similarly, many people in marginalized racial and ethnic groups face discrimination, which is associated with increased depression risk.6 

Get help now 

Browse our directory to find a therapist in your area. If you’re in crisis or having thoughts about suicide, help is available now. Please call the 988 Suicide & Crisis Lifeline at 988 or 1-800-273-TALK (8255) for free, confidential support 24 hours a day, 7 days a week, or text HOME to 741741 for the Crisis Text Line

Read Part 2 of this article to learn more about how depression is diagnosed and treated. 

About the author

The editorial team at works with the world’s leading clinical experts to bring you accessible, insightful information about mental health topics and trends.

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