Depression is the most common disability. Approximately 350 million people worldwide suffer from depression (What is Depression?). Depression is a mental disorder that can affect a person emotionally, physically, and behaviorally. Someone suffering from depression experiences severe feelings of distress, despair, and is uninterested in activities that were once appealing. People living with depression may feel like there is nothing to live for, worthless, and have trouble continuing with daily duties. Signs of depression may include irritability, restlessness, change of sleeping patters, change of appetite, suicidal thoughts, pain, anxiousness, and problems with concentration (Depression (major depressive disorder)). Depression, also known as major depression, major depressive disorder, or clinical depression, comes in all forms and severities. For instance, persist depressive disorder is a state of depression that persist for two year, and psychotic depression is where a person might experience depression combined with a type of psychosis(Depression). Depression can lasts for weeks, months, or years and can occur once during a person's life or may be persistent. There is no true understanding of the biological systems underlying depression, however there is a lot of ongoing research to comprehend what may cause depression (What is Depression?). .
There is no found etiology for depression, but is found to be caused by a mix of factors: biology, psychology, genes, and environment (Hasler, G. , 2010). It is difficult to determine the cause for depression since it varies from person to person. Biological differences such as the physical alteration of the brain responsible for mood, thinking, appetite, sleep, and behavior have been found in people with depression (Depression (major depressive disorder)). Also, differences in brain chemistry such as a chemical imbalance of a specific neurotransmitter like serotonin, norepinephrine, and dopamine have been found in people suffering from depression (Hasler, G.