Certain physical or biological factors can trigger or later contribute to mental illness. They include:


Studies have shown that many mental illnesses tend to run in families. Some of the most revealing studies have come from identical twins who did not grow up in the same households. Despite growing up under different conditions, when one twin has major depression or bipolar disorder, the other has a much higher chance for also having the same or a similar disorder. This suggests a genetic component to mental illness.

Researchers think, however, that multiple genes influence a person’s likelihood of developing a mental disorder. This means it’s unlikely that we’ll ever find a single “depression” gene or an “anxiety” gene.

Prenatal Damage

It has been proposed that damage to the developing brain before birth can increase the likelihood for various mental disorders, including schizophrenia and autism.

Infectious Diseases

Some infectious diseases can damage the brain, and this, in turn, can either cause mental illness or worsen existing symptoms. One disorder caused a strain of the Streptococcus bacteria that has been tied to the development of obsessive-compulsive disorder and other mental illnesses in children.

Physical Trauma and Brain Injury

Certain types of brain injury, from accidents, for instance, or strokes, have been linked to mental disorders. Brain injury can also arise from exposure to toxic substances such as lead.

Health Problems

People who suffer from other serious health problems, such as heart disease, might be at higher risk for developing depression or other mental disorders. Poor nutrition may also be related to certain mental illnesses.

Substance Abuse

Chronic, long-term use of alcohol and drugs can significantly increase the likelihood that a person will experience depression, anxiety and other mental disorders.

Last Reviewed: June 10, 2014