What is depression? (The Scientific Definition)

Theresa Nguyen, LCSW, Mental Health America

People who feel depressed often describe feeling sad, empty, or irritated. Feeling sad is a normal human experience, but feeling too much sadness can cause distress and life problems. When too much sadness effects your life, you might have depression.

Depression is a type of mental illness where people feel sad for long periods of time (more than two weeks).  A person could have depression if they are experiencing changes that are not normal for them and if these changes don’t go away.

The symptoms that people with depression experience include:

  • Feeling or appearing low, empty, or irritable most of the day every day;
  • Having less interest in everyday activities;
  • Changes in appetite or weight;
  • Changes in sleep – either not being able to sleep or sleeping too much;
  • Changes in activity – feeling restless inside or feeling sluggish;
  • Feeling tired or low energy;
  • Feelings of worthlessness or guilt;
  • Difficulty thinking, concentrating, or making decisions; and
  • Thoughts of death.

Life Problems

For people who have depression, the symptoms cause serious problems in their lives. The depression causes them to withdraw from others in their lives like their family, friends, or partners. Many people who have depression have a hard time in school or work. They miss assignments, can’t concentrate on their work, or feel overwhelmed by activities. This can lead to missing school or work.

Stress and Anxiety

It isn’t uncommon for people with depression to also feel really stressed or have worry (anxiety). People who have depression first and stress or anxiety second often feel like they worry about their depression, can feel the depression is coming on, or worry that the depression won’t go away.

Thoughts of death

People with depression often think about death. Thinking about death isn’t always about suicide. Many people report thinking about not existing or wondering if the world would be better without them. If there are suicidal thoughts and a plan – it is important to reach out and get help. Call the National Suicide Prevention Lifeline at 1-800-273-8255.

What else can it be?

  • Using drugs or medications that make you feel low can look and feel like depression.
  • Having another medical problem (like inflammatory disease, pain, or hormone changes) can cause you to feel depressed.
  • People with other mental health problems can also experience depression (like bipolar or psychosis).
  • If you’ve lost a loved one or are grieving a change in your life – you can feel sad, but it might not be depression unless it doesn’t get better after a long period of time (more than two months).

Treatment & Resources