The causes behind psychological disorders are complex. A person’s environment, culture, and life experiences contribute to mental health concerns. Some of these factors may protect against mental illness, while others increase the risk for developing a disorder.

Genetics and biology play a major role in mental illness. Many mental illnesses are more common in people who have a close relative with the same condition. Certain genes can increase the risk for developing a mental illness, and these genes can be triggered by environmental or biological factors. Some mental illnesses are linked to abnormal functioning of specific brain circuits or pathways. Others are linked to changes in brain chemistry, particularly the levels of certain chemicals called neurotransmitters that carry messages between nerve cells.

Some of these conditions include schizophrenia, bipolar disorder, depression, obsessive-compulsive disorder, and phobias. Symptoms of a mental illness may be mild or severe, and they can range from periods of extreme activity and heightened mood to episodes of lethargy and sadness. Some conditions cause a person to lose interest in their daily activities and feel like they can’t get through the day, whereas others can lead to self-harm or suicide.

Some socioeconomic factors, such as poverty, head trauma, poor nutrition, and exposure to toxins (such as tobacco smoke or lead), can increase the risk for developing a mental health condition. However, it is important to note that not everyone who experiences these factors develops a mental health condition. Major stresses, such as death or divorce, work-related stress, and problems in family relationships can trigger mental illness in some people.