The banner hung from a third-floor balcony, unfurling itself almost all the way down to the cobbles of the square. Barcelona no està en venda, it read, in large hand-painted letters: the city is not for sale. It wasn’t the first such slogan we’d seen in only an hour or so strolling around the narrow, winding streets of Barcelona’s beautiful old quarter last week, and naturally our curiosity was piqued. Something to do with gentrification, or developers maybe? Well, partly. But, disconcertingly, it turned out to have quite a lot to do with people like us, and possibly you too.

Or to be more precise, with the multibillion-pound global phenomenon that is Airbnb. As it happens, I’m boringly old school enough to have stayed in a hotel this time, but the airport bus was full of young families chattering about picking up their flat keys via the site that is famous for letting people rent their houses out to strangers. And Barcelona is far from the only place in which Airbnb is accused of turning summer sour.

Amsterdam is heavily restricting short-term lets by residents after street protests against the swamping of the city by tourists last year. It’s the same story from Paris to Berlin, Venice to Lisbon. Even in Cornwall, at the height of this summer’s heatwave, tourist chiefs took the unusual step of asking holidaymakers to avoid some popular beaches after coastal roads became gridlocked, leaving locals struggling to get on with their daily lives. People in Cornwall are more than used to being overrun in August, but lately something seems to be upsetting the eternally delicate balance between grockle and local, and chief suspect seems to be an unplanned, somewhat unpredictable explosion in Airbnb lets on top of the longstanding hotel and holiday cottage trade.

Profiteers make a killing on Airbnb – and erode communities | John Harris Read more

At least in the West Country things tend to calm down in September. Barcelona is a city-break destination practically all year round, which means it’s struggling with more than just a surfeit of drunken stag parties and queues outside tapas bars. Landlords have realised they can make more money out of short lets to well-off Airbnb users than from renting to conventional tenants who live and work in the city year round, so when contracts come up for renewal it’s not uncommon to find the rent suddenly shooting up to levels that young Spaniards can’t pay. Once they’re forced out of the neighbourhood, the empty flat promptly disappears into what’s still sometimes euphemistically known as the “sharing economy”, although what happens next sounds like the antithesis of sharing. Those lucky enough to own a desirable property get steadily luckier, by pimping it out to the highest bidders. Meanwhile, those who don’t have such an asset become ever less likely to get one, as property prices are pushed up across the city. Thus does inequality harden, and resentment deepen, while the failure of mainstream parties to solve the problem drives the young and frustrated ever closer to the political fringes.

The young woman in a Barcelona barber’s shop who matter-of-factly explained what the slogans were about, while running her scissors over my husband, had long ago given up on buying in the city where she grew up. But now she’s not even sure how long she’ll be able to rent. The tourist’s dilemma has always been that descending on idyllic places tends to ruin them for people who live there, but what’s unusual in this case is that the effects run so deep.

So much for the earnestly hippyish vibe of the original Airbnb model, which was supposed to be all about creating a cosy-sounding “global community” by linking up adventurous strangers in search of more authentic, home-from-home travel experiences. And so much, too, for the idea of democratising the travel industry by letting the little guy make a buck on the side. In some tourist hotspots Airbnb is now morphing from an amateur operation into a slick professional one, with landlords amassing multiple properties just as they once did with buy-to-let, and using agencies to manage their burgeoning empires.

The romantic, if sometimes risky, fantasy of swapping lives with a local for a few nights and seeing the city through their eyes is being replaced with a more corporate, impersonal experience. Sign here for the keys; check out promptly in time for the next guest to arrive. Too bad that what could have been a young couple’s starter flat is now just another asset to be sweated, and one that probably stands empty half the time.

Facebook Twitter Pinterest ‘Along with other Spanish cities, Barcelona has moved to limit the Airbnb effect, with licensing schemes and curbs on new rentals in the old town.’ Photograph: Alamy

And if it’s uncomfortable knowing that your cheap getaway comes at such a hidden cost, guilt seems unlikely to put many travellers off. After all, pangs of conscience about climate change didn’t stop millions of us taking cheap no-frills flights back in the days when it was easyJet that was disrupting the holiday market. But this is about more than what individuals choose to do with their summers. It’s about how modern markets function, and what happens when governments either won’t intervene or can’t quite work out how to do so quickly enough. Along with other Spanish cities, Barcelona has moved to limit the Airbnb effect with licensing schemes and curbs on new rentals in the old town. But if we’ve learned anything from the Ubers and the Amazons and the Facebooks, it’s that by the time the unwanted human consequences of digital disruption become obvious, much of the damage is often already done.

EU blocking cities' efforts to curb Airbnb, say campaigners Read more

What really struck the Barcelona hairdresser, however, was that when she travelled she heard similar stories. Cities all over the globe seem to be eating themselves, squeezing out the young and the skint and the creative, who are all too often the people who made them achingly hip in the first place. It manifests itself differently in different places, of course: London had a housing affordability crisis before Airbnb was even invented. Soaring prices from Berlin to Vancouver to Sydney have been blamed on everything from cheap borrowing and foreign speculation to changing demographics and government failure to build enough social housing, none of which are remotely the fault of second-home owners turning a quick profit.

But the common thread is a sense that, for whatever reason, markets are not delivering for the young in a post-crash world; that digital disruption only makes things more unpredictable; and that years of politicians earnestly promising to do something about it have come to pitifully little. All of which is a statement of the bleeding obvious now, a truth so universally accepted that it’s almost completely lost its power to shock – until seen from a slightly fresh perspective. But then that’s the thing about travel. Sometimes you go halfway round the world only to notice what was under your nose all along.

• Gaby Hinsliff is a Guardian columnist