That is SO unfair - Researchers have stumbled on the cause of teenage angst. Sheryl Smith, from SUNY Downstate Medical Centre in New York, has found that a hormone called THP or allopregnanolone, which normally provokes mental calm in adults has the opposite effect in the teenage brain. At around the time of puberty there are significant increases in the levels of a cellular receptor (docking station) for the nerve chemical GABA. This is especially marked in a part of the brain known as the limbic system, which controls emotion. THP usually increases the activity of this GABA signalling system, which in turn helps to reduce anxiety and act as a natural stress buster. But during puberty it has the opposite effect and instead makes the brain's emotional centre more excitable, triggering anxiety and mood swings. Thankfully, parents can breathe a collective sigh of relief, because the effect is only temporary (except amongst men in whom it seems to get progressively worse with age)!