Sadness

• Teens can feel pressure to "fit in," to succeed at school and to please their parents among many other expectations. If they don't feel they are meeting their own expectations, it can cause an already volatile teenager to feel a great deal of sadness. Sadness is a healthy reaction to a feeling of disappointment, but should be monitored closely by parents for signs of depression.
  
  

Anger

• Along with sadness, anger plays a key role in the development of a teen learning to cope with the highs and lows of growing up. A teenager may lash out toward a parent, a teacher or a fellow classmate following a perceived failure or letdown. While anger and fits of rage are common and even healthy if managed correctly, prolonged anger or violence should alert a parent to the possibility of an even bigger underlying issue.
  
  

Joy

• Being a teenager is one of the most memorable stages of life. Along with the lows of sadness and anger, a typical and healthy teenager will also experience periods of extreme happiness and joy. A variety of things will affect a teenager's sense of happiness, among them making new friends, making a sports team, the recognition of a first crush or a good report card. But with all radical feelings, a teenager's mood must be watched closely for signs of more serious mood disorders, like depression.
  
  

Biology

• According to Harvard Medical School's Health Publication, inner biology can play just as big a role in a teenager's mood swings as outside influences. Puberty occurs during the teen years, and brings with it a change in physical appearance and chemical levels. Testosterone and estrogen can radically affect the mood of a teenager while simultaneously giving birth to physical changes like acne and pubic hair. It is important to assure your teenager that these changes are normal, and as always, monitor the teen for signs of a more serious affliction.