They have a reputation for being sulky, uncommunicative and argumentative little brats. But according to scientists, blaming teenagers for their tantrums and mood swings is - in the words of Kevin the teenager - "just SO unfair".
Their petulant behaviour is all down to an unexpected chemical reaction in their developing brains. Scientists have found that the mechanism normally used by the brain to calm itself down in stressful situations seems to work in the opposite way in teenagers, making them even more anxious.

When the brain senses a stressful situation, it reacts by switching on receptors, using a range of chemicals, including a steroid called THP. In an adult or even a younger individual, THP would reduce anxiety. But in experiments on adolescent mice, THP increased anxiety.

The experiments, by Sheryl Smith, a physiologist at the State University of New York, offer the first physiological explanation for adolescent mood swings. Previous work has focused on analysing behavioural changes in teenagers during adolescence. Her results are published today in Nature Neuroscience.,00.html