Depression or major depressive disorder is a medical illness that negatively affects how you feel, think and act. Depression causes feelings of sadness and on occasions a loss of interest in activities once enjoyed. It can also lead to a variety of emotional and physical problems and can decrease a person’s ability to function at work, school or home. Depression can lead to low self-esteem, changes in appetite (weight loss or gain), trouble sleeping or spleeping too much, loss of energy, difficulty thinking, concentrating or making decisions and thoughts of death or suicide. Depression affects an estimated one in 15 adults in any given year. And one in six people will experience depression at some time in their life. Depression, on average, first appears during the late teens to mid-20s and is more likely to affect women than men. Some studies show that one-third of women will experience a major depressive episode in their lifetime. Teenagers are the most likely to be affected by depression due to the stress of body changes, as well as increased independence and changes in their relationships. Depression may be a reaction to environmental stresses, like verbal, physical, or sexual abuse, the death of a loved one, school problems, or being the victim of bullying. Gay, bisexual, and transgender teens are at higher risk for depression, thought to be because of the bullying by peers and potential rejection by family members. Depression is among the most treatable of mental disorders. Between 80 percent and 90 percent of people with depression eventually respond well to treatment and almost all patients gain some relief from their symptoms.