People of all ages, cultures, background and experience are susceptible. Symptoms may vary. A depressed person may not be able to shake off their gloomy feelings - even if good things are happening to them. It may be that someone starts feeling depressed for no apparent reason at all. Or, a person may start off by only feeling a little bit down, but as time goes on it gets worse.
Depression can be serious but it can be treated.
It is caused by chemical changes in the brain, and these changes alter the way people respond to their world. Sometimes the way a person reacts to stress is partly shaped by a person's genetic background. Sometimes, life history is important. For example, having unhappy experiences in childhood may increase the chances of having depression later in life for some people. Because there is no single one cause of depression, and people react to stress and strain in different ways, someone may not even recognise depression in themselves.