Behold, the most serious challenge to the Royal Society in that august body's 350-year history - the medical musings of Madonna, Gwyneth Paltrow and Stella McCartney. These women are not just singers, or actresses, or fashion designers. They are distinguished professors at the University of Celebrity, and are coating your understanding of science like a totally amazing organic body oil.

On top of this, they are best friends, so we can say their pronouncements are peer-reviewed in the best sense of that term. Can you imagine their gatherings? It must be as if Isaac Newton were taking antioxidant tea with Robert Koch and Marie Curie.

We shall come to her latest discoveries shortly, but by way of background, do recall that Gwyneth has formerly claimed that eating "biological foods" can prevent cancer, reminding us that starring in Iron Man and maintaining a glittering career in clinical research are not mutually exclusive. Then we have Madonna, who has cited the extraordinary healing powers of Kabbalah water, which costs $4 a bottle, is said to have had energy injected into it, and may or may not have been blessed by the former insurance salesman who dreamed up her religion.

Other fields of specialism? Alas, Lost in Showbiz hasn't the space today, but Madonna has previously championed a soi-disant scientist who claims to have reversed the second law of thermodynamics. And then there's Stella, who launched her organic skincare range with the warning that "lots of skin products use the same petrochemicals as the antifreeze in your car!", and is one of those celebrities who thinks they eat "chemical-free" food and use "chemical-free" products. I beg you not to tell her that water and trees are made of chemicals. The shock could finish her off.

So then to Gwyneth's latest thesis, published not in the British Medical Journal, surprisingly, but in Goop, the newsletter she sends out to her flock every week. According to Gwyneth, she bowed to crushing demand for this service from friends who were always asking her for restaurant recommendations and low-fat recipes and where to find reproduction art-deco taps. It is now Earth's most invaluable resource for all those unable to locate the perfect £650 cashmere egg cosy (remember: never eat the yolk, it gives you Aids or calories or something).

Entertainers being what they are, it was only a matter of time before Gwyneth branched out into bacteriology, and in her most recent communique she is good enough to explain her fears that household products are causing autism and cancer in children.

"A couple of years ago," she writes, "I was asked to give a quote for a book concerning environmental toxins and their effects on our children."

But how preposterous. I assume she replied: "I am an actor. My job is pretending to be other people. This does not qualify me to discourse on paediatric medicine"? Alas not.

"While reading up on the subject, I was seized with fear," Gwyneth continues. Lost in Showbiz hasn't the strength to bore you with it in full, but it's something about foetuses and young children being unable to "metabolise toxins" - toxins that come from all the "chemicals" we fill our environment with. "The research is troubling; the incidence of diseases in children such as asthma, cancer and autism have shot up exponentially ..."

No matter that there has been very little change in the rate of childhood cancers detected in recent years, and no matter that various leading experts have exploded in exasperation at Gwyneth's general hokum. Like her coterie of fellow scientists, she is indifferent to the critics, whom the form book suggests she would dismiss as "haters".

So if you hear anyone disparaging our three brainiacs, you tell them this: if we understand more than we did five years ago about how holy water can cure verrucas and how shampoo causes cancer, then it is because we are standing on the shoulders of these giants.

• Marina Hyde's book, Celebrity: How Entertainers Took Over The World And Why We Need An Exit Strategy, is published by Harvill Secker