Researchers from the New York University found that a hormone which usually calms a person's anxiety is reversed when that person is going through puberty - making them even more irritable.
The THP hormone works to relive stress in young children and adults. It actually acts as a tranquilizer and helps people deal with stress.
The study, published in Nature Neuroscience, said the effect the hormone has on teenagers may be reversible or blocked all together. However, scientists say that at the very least, their discovery will help adults understand their difficult teen better.
Researchers were able to see the hormone in effect during a mouse study. Lead study author Dr Sheryl Smith suggested that this happened because of all the other hormones active during puberty.
She said, "This research has revealed that there is a biological basis for a teenager's mood swings. They can be frustrating for parents and teachers - as well as the adolescents. As adults, we just deal with things, but it is harder for teenagers because of their biology. I think it's important for people to know that."
