Under the big tent of depression there are many shades of gray. Depression can be mild or severe. It can be short-lived or chronic. Special circumstances, like the birth of a baby or the changing of the seasons, can trigger depressive symptoms.

Understanding the type of depression a person is experiencing helps doctors determine treatment. And for people who are diagnosed with depression, having information about their specific disorder can be helpful.

Here’s what you should know about the different types of depression. If you suspect you or a loved one has one of these, get evaluated by a mental health professional. They can help you figure out a diagnosis – and the best course of treatment.

Major depressive disorder

This very common type of depression is also known as major depression or clinical depression. Under diagnostic criteria, people must have at least five symptoms persisting for two weeks or longer to be diagnosed with major depressive disorder. Those symptoms can include feelings of sadness, emptiness, worthlessness, hopelessness, and guilt; loss of energy, appetite, or interest in enjoyable activities; changes in sleep habits; and thoughts of death and suicide. Most cases are highly treatable.

Subsyndromal depression

A person who has depressive symptoms but doesn't quite check all the boxes for a diagnosis of major depression may be deemed “subsyndromal.” Maybe she has three or four symptoms, not five, or maybe she’s been depressed for a week, not two.

Bipolar depression

Wide swings in mood and energy, from elation to hopelessness, are the signature of bipolar depression, also called bipolar disorder or manic-depressive illness. To be diagnosed with this form of depression, a person must have experienced at least one bout of mania.

Disruptive mood dysregulation disorder

Screaming and temper tantrums can be features of disruptive mood dysregulation disorder (DMDD), a type of depression diagnosed in children who struggle with regulating their emotions. Other symptoms include an irritable or angry mood most of the day nearly every day and trouble getting along in school, at home, or with their peers.

Postpartum (or perinatal) depression

The birth of a baby brings enormous joy but can sometimes lead to postpartum depression (PPD), a type that affects one in four women and one in eight men. In women, postpartum depression is likely triggered by shifts in hormones, fatigue, and other factors. In men, it’s environmental, brought on by shifting roles and lifestyle changes that come with parenting.

Psychotic depression

People with psychotic depression have severe depression accompanied by psychosis, which is defined as losing touch with reality. Symptoms of psychosis typically include hallucinations (seeing or hearing things that aren't really there) and delusions (false beliefs about what's happening).

Treatment-resistant depression

Sometimes people with major depressive disorder don’t readily respond to treatment. Even after trying one antidepressant and then another their depression stubbornly hangs on.

Seasonal affective disorder

Seasonal affective disorder (SAD) is a recurring type of depression that usually strikes in the fall or winter. Along with a change in mood, SAD sufferers tend to have low energy. They may overeat, oversleep, crave carbs, gain weight, or withdraw from social interaction.