Why might adolescence be a stressful time for many teenagers?

Adolescence can be a stressful time for many teenagers because this is a period of their lives when they start going through many changes, which are often physical, mental, and emotional. Their bodies start to change, and so do their feelings and understanding of the world around them. This is the time when it is expected of them to act in a mature and adult way, yet nobody yet takes them seriously and treats them as if they were still children.