A person who is considered 'mentally healthy' is someone who can cope with the normal stresses of life and carry out the usual activities they need to in order to look after themselves; can realise their potential; and make a contribution to their community. However, your mental health or sense of 'wellbeing' doesn't always stay the same and can change in response to circumstances and stages of life.
Everyone will go through periods when they feel emotions such as stress and grief, but symptoms of mental illnesses last longer than normal and are often not a reaction to daily events. When these symptoms become severe enough to interfere with a person's ability to function, they may be considered to have a significant psychological or mental illness.
The exact cause of most mental illnesses is not known but a combination of physical, psychological and environmental factors are thought to play a role.
Many mental illnesses such as bipolar disorder can run in families, which suggests a genetic link. Experts believe many mental illnesses are linked to abnormalities in several genes that predispose people to problems, but don't on their own directly cause them. So a person can inherit a susceptibility to a condition but may not go on to develop it.
Psychological risk factors that make a person more vulnerable include suffering, neglect, loss of a parent, or experiencing abuse.
Difficult life events can then trigger a mental illness in a person who is susceptible. These stressors include illness, divorce, death of a loved one, losing a job, substance abuse, social expectations and a dysfunctional family life.