Everyone feels sad or “blue” from time to time for a few days or weeks. Depression is when these feelings don't go away and they interfere with daily life. Depression is a real, serious illness, just like diabetes or heart disease. It can develop at any age. It is one of the most common mental health problems in the U.S. Depression makes you feel sad, helpless, anxious, or hopeless. It gets in the way of your life and relationships. Depression causes chemical changes in the brain that inhibit your ability to think and act. But, with help, you can feel better again.