CELEBRITIES have their uses. Their lives can be prodded and paraded as a form of mass entertainment. Sometimes they are even good at whatever it was that got them noticed before they became elevated to the vacuous stratosphere of simply being famous.

Oh, but what privileges are granted to those who breathe the heady air up there. Once gulped deep into the lungs, the oxygen of fame refreshes the parts ordinary air can't reach. Perhaps that is why the famous can get away with speaking such nonsense - and, not only that, but the world sits at their feet and laps up whatever preposterous notions spout (witness Tom Cruise and his daffy proclamations about the creepily wacky "religion" of scientology).

The media plays a part in all this, giving the famous platforms from which to dottily proclaim. Yet any journalist who has interviewed the famous, or any TV viewer who has watched Jonathan Ross do the same, knows an obvious truth. Some celebrities are full of fascinating things to say, while others wouldn't know an interesting thought if it bit them on their surgically enhanced bottom.

Sadly, assorted celebs do like to sound off about science, especially in relation to health, proclaiming this or that theory with breezy confidence, without bothering to check first with someone who might know - such as, oh, a scientist.

The charity Sense About Science is worried about the ability of celebrities to talk nonsense about science. So it has published a new leaflet aimed at debunking unscientific comments made by the famous.

Examples used in the leaflet include Madonna uttering rubbish about nuclear waste. "That's something I've been involved with for a while with a group of scientists - finding a way to neutralise radiation," the singer is quoted as saying.

Sense About Science offers a rebuttal from Nick Evans, environmental radio-chemist at Loughborough University, who points out that radioactivity "cannot be neutralised', it can only be moved about from one place to another until it decays away at its own rate. It comes in many different types: some last for billions of years, other decay away in a few minutes. There are no magical solutions."

No magical solutions! - how boring is that to a middle-aged pop princess who wafts in on a passing breeze with the solution up her sleeve.

Now if you want advice on how to spread a thin musical talent over a few decades, then Madonna is your woman. But if you want to know about radiation, ask an expert rather than someone who can admirably still do the splits and sing at the same time a year or two off 50.

The ever-annoying Heather Mills McCartney is slapped down for saying rising levels of obesity in children can be traced to drinking milk. This, according to physiologist Philip Coan, it just not true - "A US study found no link between increases in child weight and increases in drink consumption".

Carole Caplin, lifestyle guru to Cherie Blair, said women wishing to avoid breast cancer should be "keeping the lymph system clear and unclogged". To which Michael Baum, emeritus professor of surgery at University College London, ripostes: "Carol's idea has no meaning whatsoever. It is not based on knowledge of anatomy or physiology of the human body, let alone of breast cancer."

Joanna Lumley gets a similar rebuff for saying that "cancer is roaring ahead at the moment" because of chemicals fed to animals. John Toy, medical director of Cancer Research UK, points out that cancer is not "roaring ahead" at all, but is rising because people are living longer.

All this wouldn't matter too much if we didn't give such regard to what celebrities say. Once a scientific untruth has been uttered in print or on television, it is out there and becomes accepted as the truth by people who would rather listen to the thoughts of the famous on health, diet and disease, instead of to little-known experts who have wasted their lives in studious scientific investigation. As Sense About Science warns: "If it sounds too good to be true, it usually is."