On the subject of anger, I have a self-serving theory, which is that my quickness to become furious about petty matters - chiefly, the price of train tickets and the strange way that any street I move to instantly becomes the site of major construction works - is actually a good thing. After all, doesn't it show that I'm fortunate enough not to harbour far deeper, more destructive rages against my parents or bullies from childhood or society in general? I realise there's an alternative interpretation, which is that I'm just an irritable curmudgeon. But that isn't half so consoling whenever I find my fists involuntarily clenching as some train company executive explains that it's easy to travel cheaply as long as I book eight years in advance.

What one should do on such occasions, self-help authors have always claimed, is find a harmless way to vent. "Punch a pillow or a punching-bag," writes John Lee in Facing The Fire. "Punch with all the frenzy you can. If you are angry at a particular person, imagine his or her face on the pillow or punching-bag... You will be doing violence to a pillow or punching-bag so that you can stop doing violence to yourself by holding in poisonous anger." This is the "catharsis hypothesis" - the idea that it's better out than in - and in the world of pop psychology it has the status of an article of faith. It gets applied to worry, too, which explains "a problem shared is a problem halved". But the real problem, it turns out, is with the hypothesis itself. (Also: who actually owns a punching-bag?)

We're so accustomed to thinking of our emotions using the metaphor of a pressure-cooker, or a bottle with a cork in it, that we're barely aware we're doing it. According to this "hydraulic metaphor", emotion "builds up inside an individual, similar to hydraulic pressure in a closed environment", the anger researcher Brad Bushman says. "If people do not let their anger out, but try to keep it bottled up inside, it will eventually cause them to explode in an aggressive rage."

But Bushman's experiments, and a string of others since the 50s, show that venting makes things worse. In one classic study, participants were insulted, then some were allowed to hammer nails into wood for several minutes. Subsequently, given the chance to criticise the person who insulted them, the nail-pounders were significantly more hostile. Maybe the hammering provided some physiological relief, but their underlying anger had been stoked. Rather than punch a pillow, Bushman recommends doing something incompatible with anger, such as reading or listening to music. That won't address the cause of the anger, of course, but it will leave you in a better frame of mind to do so.

Likewise, a study last year focusing on teenage girls concluded that the obsessive discussion of worries - "co-rumination" - often exacerbated negative emotions: a problem shared isn't always a problem halved. This isn't an argument for bottling things up: talking, obviously, is a crucial way of finding solutions to problems. But it may be an argument for realising that we're much more complex than bottles.

oliver.burkeman@theguardian.com