As we walk into any bookshop for an impulse purchase, we base our choice on the same superficial attractions as a Casanova walking into a singles bar. And all the new places where books are now sold — the internet, the bookshop’s three-for-two tables, the supermarket — are making us even more likely to judge a book by its cover.

Take Georgette Heyer, the slightly frumpy historical novelist. When her publishers changed all her cover art last year, the classy new Jane Austen-ish look doubled her sales. Haruki Murakami has just been given a complete makeover, and next month Lesley Pearse, Penguin’s much-loved women’s author, is to get the same treatment.

“All the research shows that consumers are very, very influenced by the covers, not necessarily to buy a book, but to pick it up,” Joanna Prior, publicity and marketing director at Penguin, says.

Studies show that a book on a three-for-two table has about one and a half seconds to catch a reader’s eye. If it is picked up, it is on average glanced at for only three to four seconds.

“More than ever a book has to say ‘Buy me! Buy me!’, it really has to seduce,” Prior says.

As readers, we get sentimental over our long-term relationships with covers, the way that our personal edition becomes indelibly and nostalgically associated with the work, and authors too often feel the cover should be a romantic embodiment of their creation. DBC Pierre said that he designed a cover (not used) for his Man Booker prize-winning Vernon God Little before he wrote a word.

Publishers are increasingly appreciating the power of the artwork as advert, right down to the present angstfest over what appears on the a book’s spine. This is why we see more and more of what the trade calls re-jacketing: we don’t judge a book by just its cover any more, but by a succession of covers.

So far this sounds like any other marketing exercise, but that is to underestimate the mysteries of the book-buyer’s heart. It’s about a century since dust jackets were introduced to protect a book on the way home from the shop, but still no one has fathomed what makes certain covers sell and others hang around on the shelf. The process of rejacketing Pearse’s work began not with advertising executives, but an invitation from Penguin to some of the author’s most loyal readers to work with them on the redesign. As a result, off came the gold foil lettering, the stark photo of a woman’s face, for a prettier, more upmarket look.

“We are not sure of the reasoning, but we know that the fans responded well to the new covers,” Prior says.

The unknown chemistry between words, jacket and reader is a theme that recurs again and again. Derek Birdsall, regarded by many as the godfather of modern cover art, having designed many of the coolest covers for Penguin in the 1960s, thinks we should not even try to work it out. Modern covers tend to be a bit too overwrought — “disappearing up their own arse,” he says. “A good cover is obvious but without too much rationality.”

In Front Cover, his recent book on the phenomenon, Alan Powers called this “it factor” the “hidden eroticism” of a good cover, “connecting with some undefended part of the personality in order to say ‘take me, I’m yours’ ”.

This mystery over the relationship between cover and reader makes the industry rather conservative, says Powers. After meetings at which the views of the art director, the editor and, increasingly, the author battle it out with a powerful sales team, “it is amazing that there is any kind of innovation at all; there are a lot of very standard jackets around”. One jacket even had “design by committee” printed on the back as the art department’s little joke.

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