Depression is a mood disorder that affects a person's personality, interpersonal communication, learning, work, school, eating, general health, and can last from weeks to a lifetime. It is commonly experienced between ages 20-40 and has biological, evolutionary, hereditary, psychological, social, and medical causes that bring down one's spirit, mood, self-esteem, and interest through impacts on serotonin, norepinephrine, and dopamine levels in the brain. Left untreated, depression can increase risks of suicide and shorter life expectancy.