Like the hula-hoop, skateboarding and computer games, sexting is one of those teenage fads which has spread unexpectedly into the adult world. There was a time when talking dirty by text – or, more challengingly, within the 140-character form of Twitter – appealed mostly to those not getting the real thing.
Now, increasingly, the grown-ups are giving it a try. The habit of having a mental, virtual legover via a mobile phone has become a cheerful, modern form of flirtation. A survey last week claimed that two million women have caught their partners at it. In America, there are discussions as to whether there should be legislation to cover individuals sending naked photos and videos to one another. Here, it has become the mini-scandal most likely to catch out errant minor celebrities.
Earlier in the year, the TV presenter Vernon Kay was found to have sent "racy texts" to a model, while the footballer Ashley Cole, something of a sexting addict, was discovered sending naked pictures of himself to the inevitable "mystery blonde".
The comedian Jason Manford recently lost a job on the BBC's The One Show having sent saucy messages to a fan, requesting photographs of her in her underwear. How weirdly old-fashioned they sound, these "racy", "saucy" adventures – they are not unlike the sort of furtive, feverish letters which used to be published in magazine like Readers' Wives and Forum.
Indeed, the media have been amusingly muddled in their reaction to texting scandals. On the one hand, it was recognised that sexting is a form of infidelity; on the other, imagined sex, however mucky, has to be rated lower on the tabloid shock-horrorscope than the type that involves two people being in the same room at the same time.
The great sexting craze takes us one step closer to science-fiction visions of futuristic sex in which all normal human contact is removed. Just as Facebook imitates friendship with an easier, more addictive virtual version, so erotic or quasi-erotic interaction through a phone or computer offers sex without the more demanding physical stuff, the risk of embarrassment or failure, the effort, the mess.
Social networking revolves entirely around the self, encouraging the user to answer that all-important question: "What's on your mind?" and share every passing thought with the outside world, and sexting plays the same trick: it changes a relationship from being an encounter shared by two people, however briefly and unsatisfactorily, into something that is essentially – let's use the polite word – solipsistic. The other person involved is less a partner than an extension of the self, an aid to personal release.
It would be absurd to disapprove: self-excitement through your phone does not stunt the growth or cause hair to grow on your palms. If modern man and woman are "time-poor", what could be more efficient than instant satisfaction from a small mobile device? As one guide to sexting puts it: "Nobody indulges in cheeky banter over the photocopier any more; how laborious, when you can type out a few choice words to someone you fancy and crack on with your work while you wait for a reply."
As for teenagers, educationalists should be pleased that so many of them are exercising their imaginations and vocabularies more strenuously than they would ever do in a creative writing class. All the same, there is something peculiar and alienating about a relationship filtered through a little screen. What D H Lawrence once disapprovingly called "sex in the head" is not bad in itself, but it has the effect of making the richer human reality seem flawed, and rather hard work. Part of a pornified culture, it encourages an immature, fantasy version of sex – fine for teenagers, but harmful when it begins to infect the everyday life of adults.