What is depression?

Everyone goes through periods of sadness, discouragement, or fatigue. Depression is something else: a common illness, with causes, precise symptoms, and effective treatments. Knowing how to recognize it helps avoid mistaking it for a passing low, or experiencing it as a personal weakness.

An illness, not a state of mind

Doctors refer to a “major depressive episode” (the term used in the American classification). It is defined by persistent sadness or loss of interest and pleasure, present almost every day for at least two weeks. These come with other symptoms affecting sleep, appetite, energy, concentration, and self-esteem. These symptoms cause real suffering and difficulty in daily life: at work, within the family, in relationships.

According to the World Health Organization (WHO), depression is one of the leading causes of disability worldwide. It differs from ordinary mood fluctuations and temporary emotional reactions to life's difficulties.

Saying it's an illness doesn't mean it has a single cause. Research instead describes a combination of factors. There are biological factors: a genetic vulnerability, since risk is higher when a close relative has been affected, and changes in the functioning of certain brain circuits that regulate mood, motivation, and the stress response. There are psychological factors: personal history, difficult childhood experiences, a tendency toward self-criticism. And there are life factors: bereavement, separation, job loss, isolation, financial insecurity, burnout, chronic physical illness. Depression can also appear with no identifiable trigger, which can make it all the more confusing for the person and their loved ones.

Two common misconceptions deserve correction. The first is that you can “snap out of” depression through willpower: that's about as realistic as curing pneumonia through willpower, and this kind of advice often reinforces guilt. The second is that depression is a dead end: the vast majority of episodes resolve, especially when treated. However, the risk of recurrence is real, since about one person in two will experience another episode, which is why it's worth learning to spot returning signs early.

There are several forms. Episodes are classified as mild, moderate, or severe, depending on the number and intensity of symptoms. Some forms of depression occur in specific contexts: after childbirth, in winter for seasonal depression, or as part of bipolar disorder, where depressive phases alternate with elevated-mood phases. This last distinction matters, since treatment isn't the same.

Global prevalence

In France, according to the Santé publique France Barometer published in 2025, 15.6% of adults aged 18 to 79 experienced a diagnosable depressive episode during 2024, or nearly one adult in six. Earlier editions of the barometer gave lower figures, around 10% in 2017 and 12.5% in 2021. Since the survey method has evolved, the comparison remains approximate, but the upward trend since the health crisis is confirmed by other indicators, particularly among young adults.

In the United States, according to the national NSDUH survey, about 8.3% of adults, or 21 million people, experienced a major depressive episode in 2021. The proportion reached 18.6% among 18-25 year-olds. French and American figures aren't directly comparable, since the questionnaires and criteria differ.

At the global level, the WHO estimates in its 2026-updated fact sheet that about 5.2% of adults live with depression, or some 322 million people. This lower figure is explained by the method: it measures the number of people affected at a given point in time, not over a full year.

Beyond these differences in method, one finding is common to all these countries: depression is one of the most common illnesses, and it can affect anyone, regardless of age, background, or apparent success.

Treatment disparities

One figure from the French barometer sums up the issue: in 2024, 44% of people who had experienced a depressive episode during the year had received no care at all. That proportion reached 54% among men, and exceeded half among farmers, tradespeople, shopkeepers, business owners, and manual workers. When help is sought, the primary care doctor remains the first point of contact.

In the United States, about 61% of adults who had a major depressive episode in 2021 had received treatment. Globally, the WHO estimates that even in high-income countries, only about one person in three receives mental health care. In low-income countries, the gap is far wider.

Several reasons explain this gap. The illness itself discourages seeking help: lack of energy, guilt, and the feeling of not “deserving” help are themselves symptoms. There's also fear of being judged, the idea that one should cope alone, unfamiliarity with the signs, and also wait times for psychiatrists and the cost of visits. In men, depression more often shows up as irritability, alcohol use, or overinvestment in work, which delays recognition.

Who is most at risk

In France, women are more often affected than men, a pattern seen worldwide: according to the WHO, depression affects about 6.2% of women versus 4.1% of men. The 2024 barometer also shows a higher frequency among young adults, and greater severity between ages 18 and 59, with the highest proportion of severe episodes among 40-49 year-olds (7.1%). People facing financial insecurity, isolation, or unemployment are more exposed. Among working adults, remote workers, employees, and mid-level professionals show higher rates.

Other situations raise the risk: a chronic illness (diabetes, heart disease, chronic pain), the period following childbirth (more than one woman in ten according to the WHO), prolonged burnout, or heavy alcohol use. Depression is also more common in people who have already had an episode, which is one of the reasons follow-up after recovery matters.

Getting an objective read on your symptoms before talking about them

Faced with symptoms that persist, it can be hard to tell whether it's a period of fatigue or depression. A structured screening tool helps bring clarity and prepare for a consultation.

The PHQ-9 questionnaire, used on Hygietest, was developed in the late 1990s by an American team (Kroenke, Spitzer, and Williams) and published in 2001. Its 9 questions mirror the criteria for a depressive episode and cover the past two weeks. The total score, from 0 to 27, estimates the intensity of symptoms, from mildest to most severe. It is free of copyright, used in numerous countries, and well validated in primary care.

The PHQ-9 doesn't make a diagnosis: only a healthcare professional can do that, after an interview. But a high score is a serious reason to talk to your doctor soon. If you're going through a very difficult time or having dark thoughts, don't wait for a test result: 3114, France's national suicide prevention line, answers free of charge day and night.

To assess your symptoms, take the “Am I depressed?” test.