Cancer care doesn't have to mean grim hospital wards, believes Maggie's co-founder Charles Jencks: uplifting buildings benefit both body and soul. But are they just an architectural placebo?

In pictures: Maggie's Centres present and future

Charles Jencks would be the last person to claim that architecture could replace chemotherapy, but he's the first to argue that it can make a difference to cancer patients. As the driving force behind cancer care charity Maggie's, and a well-established architectural writer, Jencks often finds himself having to defend his views. The Maggie's Centre initiative, named after Jencks's wife, Maggie Keswick, who died of cancer in 1993, has grown from a one-off project to a mushrooming nationwide network – six existing buildings with more on the way, and a lengthening list of high-profile designers: Richard Rogers, Frank Gehry, Zaha Hadid, Rem Koolhaas. As the idea has taken off, so Jencks has come under fire from both the scientific community, who question the validity of his claims (or media distortions of them); and the design community, who wonder if Maggie's Centres aren't injecting more architecture into small healthcare facilities than they strictly need.

Jencks is not advocating some deterministic equation between architecture and health – as if the sight of a well-detailed staircase could somehow zap away a malignant tumour – but he does believes in what he calls an "architectural placebo effect". "A placebo is a phoney cure that works," he explains. "This is very hard for the medical profession to get their teeth around because they hate placebos but scientifically, placebos work in about 30% of cases that are psychogenic diseases. You have to believe in a placebo or it won't work, but if it works it's obviously working in some indirect way, through feedback in the immune system, let us say, or in the willpower of the patient to take a more strenuous exercise in their own therapy.

"You can imagine all sorts of ways in which architecture adds to the placebo effect," he continues, "and in that sense it's impossible to measure. Here's a funny insight: in a way, the carers are more important than the patients. Because if the carers are cared for, they turn up, they enjoy it and you create this virtuous circle, this mood in a Maggie's Centre which is quite amazing. So architecture helps do that because it looks after the carers. There's a lot of people who would quite rightly attack that notion, and I don't want to claim that we can yet prove it, but we hope to."

Jencks presents his case in a new book whose title succinctly sums up his approach: The Architecture of Hope. "It is my hope, and it was Maggie's hope, to live longer with cancer. And I think any cancer patient, if you dig not too deeply, they want to live. So is there an architecture that helps you live?"

If there is, Jencks argues, it is not to be found in the modern hospital. He describes the space in which Maggie herself received her weekly chemotherapy as a form of "architectural aversion therapy" – a windowless neon-lit corridor of Edinburgh's Western General Hospital. Many of us are familiar with similar spaces. In the industrial age, the design of healthcare buildings has been dictated by the demands of hygiene and efficiency: hard, sterile surfaces; bright, white spaces; long corridors; artificial ventilation systems. The template has been updated a little in the PFI age with atrium lobbies and toothpaste-coloured cladding, but these places are still overwhelmingly alienating.

Jencks and others, such as the Dutch academic Cor Wagenaar, believe that modernism created a rupture in the long, intimate relationship between architecture and health. That history stretches back to ancient Greece, where temple complexes such as Epidauros were about healing the spirit as well as the body, and even Stonehenge, which recent findings suggest may have been a hospital. Its modern roots lie in the Enlightenment, when it was first proposed that good design of the built environment could do more for public health than the medical profession could. In a way, Maggie's Centres reconnect with this "secret tradition", says Jencks. Yes, we need medical environments to cure us, but we also need to feel like people again, rather than patients. He is not alone in this. Witness the Circle group's recent hospital in Bath, designed by Foster and Partners, which feels more like a boutique hotel. They, too, are recruiting architects such as Richard Rogers and Michael Hopkins to rethink hospital design on a more humane scale. Or there's the AHMM's bright, fresh Kentish Town Health Centre, also nominated for last year's Stirling prize, or Gareth Hoskins's civic-minded health centre designs. Things are changing.

There's no great architectural secret at work in the design of Maggie's Centres. They are defined by inarguably positive qualities: light, space, openness, intimacy, views, connectedness to nature – the opposite of a standard-issue hospital environment. They are domestic in scale, centred around the kitchen, a place where you can make yourself a cup of tea and have an informal conversation. In Jencks's words, they are buildings that hug you, but don't pat you on the head. It's not just about giving people architecture, he argues – it's also providing information, relief; psychological, emotional and even financial support – all of which contribute to the urge to go on living. Nor is there any set of instructions for architects as to how to achieve these goals. Frank Gehry's building, for example, combines a crinkly-roofed fairytale aesthetic with a serene view over Dundee on one side and a garden maze on the other. Zaha Hadid's outlet in Fife has been compared to a Stealth bomber – sharp and black on the outside, but mercifully calm and light inside. More recently, Richard Rogers's London Maggie's Centre shut out the city behind rhubarb-pink walls and opened up an oasis of intimate, domestic-scaled spaces, all capped by a protective roof.

The award of the 2009 Stirling prize to Rogers's building was another gesture of approval for the Maggie's Centre approach, but it also raised the question of whether they really needed such star names to design them. In addition to the six existing Maggie's Centres, there are another six under way, including designs by Dutch superstar Rem Koolhaas, the late Japanese architect Kisho Kurokawa and some of Britain's best-known names – Piers Gough, Chris Wilkinson, Ted Cullinan and Richard MacCormac. There are plans for as many as 23 buildings further down the line, even outposts in Hong Kong and Barcelona. If the brief is so relatively straightforward, why the starchitects? Is there a danger that Maggie's Centres are becoming more about prizes than patients – a free pass for virtuoso architects to get something built?

In Jencks's defence, Koolhaas and Hadid were fellow students of Maggie's. Gehry and co were lifelong friends of the couple. They just happened to hang out with future superstar architects. Besides which, Jencks says, without the media attention generated by these names, the charity would not have attracted the public donations that are enabling it to expand. Cancer affects up to one in three adults, after all. A great many people have been affected by Maggie's Centres already, and each of the new buildings hopes to serve a catchment area of two million people. "This was not thought of way back, that architecture would make such a difference to raising money," says Jencks. "And it's a double thing: it raises our profile, but it also gives us good buildings which last, so we benefit in the long term. I can't understand why other institutions haven't done the same."