Depression may be triggered by major life events such as the death of a relative or friend. Stressful situations such as divorce, financial difficulties or job loss can also trigger depression. Depression can sometimes be caused by a person's lifestyle. Childbirth can also trigger post-natal depression in women, as can loneliness, especially in the elderly.
Over the past 20 years, scientists have been investigating the way in which some chemicals in the brain affect a person's mood. These chemicals include serotonin, noradrenaline and dopamine - depressed people are often found to have low levels of one or more of these chemicals in their brains.