The causes of mental illness are complex and it is not possible to point to one single cause. However, we are aware of many factors that contribute to mental illness; such contributors are known as risk factors. We do know that many forms of mental illness have a genetic component to them and specific genes related to the production of neurotransmitters such as serotonin and dopamine have been associated with several forms of mental illness. We also know that early childhood environment plays an important role; stable, loving environments protect against mental illness and chaotic, neglectful, and traumatic environments raise the risk of it. We also know that high levels of stress in both childhood and adulthood contribute to mental illness.

Particular disorders, such as post-traumatic stress disorder and acute stress disorder, are specifically linked to extremely stressful events. We also know that the physical environment plays a role in mental health and mental illness. Environmental toxins, substances of abuse, and even exposure to substances of abuse in utero can all contribute to the development of mental illness.