Depression is a common mental health disorder that affects more than 120 million people around the world, according to the World Health Organization. A combination of factors cause depression, such as genes, brain chemistry, environmental experiences or illness.

Genes

People with depression often have family members who also suffer from depression. As of 2010, according to the Mayo Clinic, research is being conducted to identify genes related to the illness.

Brain Chemistry

Brain chemicals known as neurotransmitters can alter a person's mood, according to the Mayo Clinic. Low levels of the neurotransmitter serotonin have been known to trigger depression.

Environmental

Life circumstances such as the death of a loved one can cause depression. Some people who face unemployment or financial problems also experience varying degrees of depression.

Illness

Depression is often related to disease. Illnesses such as heart disease, diabetes, cancer and Alzheimer's recognize depression as a symptom.

Medical

Use of certain medications can lead to depression such as prescribed medications for high blood pressure or sleeping pills.

Prevention

If depression is related to stress, learn to manage your time better, delegate responsibilities or say "no." Stay connected to friends and family during bouts of depression and seek early treatment to "prevent depression from worsening," as recommended by the Mayo Clinic.

Source:

Mayo Clinic: Depression (Major Depression)

World Health Organization: Depression

More Information:

Hope for Depression Research Foundation: Depression facts and resources