Gwyneth Paltrow threw down the gauntlet to "evil genes", Stella McCartney compared skin lotions to antifreeze, and the television presenter Sarah Beeny spoke on screen about chemical-free make-up.

Now the scientific claims of the celebrities who appear on our television screens with advice on living healthy lifestyles and avoiding toxins have been put under the microscope.

A year on from publishing a leaflet that encouraged celebrities to check their facts when talking about science, the charity Sense About Science has brought together a panel of experts to assess how Britain's actors, TV presenters and lifestyle gurus did in 2007.

In a report published today, the experts noted a welcome drop in big scientific gaffes. But they still found plenty of cause for concern. They say spurious claims about "artificial" chemicals are still going strong, as is unsupported medical advice from people who are not doctors. And confusion has endured about terms such as organic, artificial and natural.

The biggest offenders last year were Beeny and Stella McCartney. In an episode of Channel 4's programme How Toxic Are You? Beeny talked about chemical-free moisturisers and make-up. Concerning this, Ian Mabbett, a chemist at the University of Swansea, said chemicals were "everywhere and everything". He added: "To be chemical-free you have to experience a total vacuum greater than that of space."

When McCartney launched a skin-care range last spring she said many other skin products used the same chemicals as antifreeze. But Dominic Williams, a pharmacologist at the University of Liverpool, says that, alarming though this might sound, it is nothing to worry about. Propylene glycol is used widely in moisturisers, as well as for solvents for food colouring, and in anti-bacterial lotions.

There were also compliments from scientists, who say they have noted a lull in pseudoscientific claims related to vaccines such as the MMR jab.

And they praised Jamie Oliver for a discussion on chemicals in chillies. "The chemical Jamie is referring to is capsaicin," said Philip Coan, a physiologist at Cambridge University. "Japanese clinical research has showed that eating breakfast containing capsaicin has resulted in a 23% increase in diet-induced energy expenditure immediately [after] eating."

Matt Helders, drummer for the Arctic Monkeys, impressed when at last year's Live Earth concert for climate change he said "we're using enough power for 10 houses just for stage lighting".

Peter McNaughton, a pharmacologist at Cambridge University, said: "Celebrities occupy a powerful position; they have access to the media in a way that scientific experts generally do not. I am delighted that they appear to have been getting their facts straighter over the last year. Long may it continue."

Star detractions

Sarah Beeny

The charity Sense About Science said that the worst celebrity example this year was the Channel 4 programme How Toxic Are You? when the presenter, Sarah Beeny, pictured right, talked about "lovely make-up and moisturisers which don't have any chemicals in them".

Derek Lohmann, a chemist, said: "In general, throughout the programme, there is a lack of positive scientific fact. There is the usual confusion over natural and synthetic chemicals."

Stella McCartney

In an interview with Time magazine last year that coincided with the launch of her new skin-care range, called Care, Stella McCartney said: "Your skin is your largest organ, and up to 60% of what you put on it is absorbed into the system. Lots of skin products use the same petrochemicals as the antifreeze in your car!"

Gary Moss, a pharmacologist based at the University of Hertfordshire, said: "Despite starting correctly [the skin is the body's largest organ, and its most diverse], Stella's next claim has no evidence whatsoever. Generally, it is around 1% of an applied compound and that depends on the physicochemical properties, so it is usually less, overall."

Julia Stephenson

Julia Stephenson, a vegetarian celebrity and columnist on the Independent, who goes by the name of the Green Goddess, wrote about her "war on electrosmog" in the newspaper, saying: "Our unprecedented exposure to electrical equipment, mobile phones and Wi-Fi mean that we are surrounded by a soup of electromagnetic smog at all times. In effect, we live in an electro-dictatorship."

Paddy Regan, a physicist at the University of Surrey, said: "Report after report, serious scientific study after serious scientific study have failed to demonstrate any statistically significant causal link between usual, every day Wi-Fi and mobile phone use and any detrimental health effects."

Gwyneth Paltrow

The Hollywood star Gwyneth Paltrow said at a cancer conference early in 2007: "I am challenging these evil genes by natural means. I am convinced that by eating biological foods it is possible to avoid tumours."

Ursula Arens, a dietitian at the British Dietetic Association, said: "Diet cannot prevent cancer. It is reasonable that the risks of some of them can be reduced with certain diets, but some cancers, alas, show no link to dietary factors."

Gillian McKeith

Gillian McKeith, presenter of the Channel 4 series You Are What You Eat, who describes herself as a holistic nutritionist, explained the dangers of obesity among schoolchildren in Fife, Scotland, saying: "If a quarter of the kids are overweight now then when they grow up and have kids half of them will be overweight. And then if they have kids everybody will be overweight!"

John Garrow, emeritus professor of human nutrition at the University of London, responded: "Obesity is not mainly genetically determined, although it does run in families, because members of families share a similar environment."

Nintendo

Nintendo's game called Dr Kawashima's Brain Training is based on the premise that cognitive exercise can improve the brain's performance. It has been promoted using a galaxy of stars. Nicole Kidman said: "I've quickly found that training my brain is a great way to keep my mind feeling young."

Julie Walters, Phillip Schofield, Fern Britton, Zoe Ball and Johnny Ball have endorsed the product and Patrick Stewart told the Sun: "Getting my brain age down to 33 has become a fascinating and stimulating way to relax."

Jason Braithwaite, a cognitive neuroscientist at the University of Birmingham, said: "There is no conclusive evidence showing the continued use of these devices is linked to measurable and general improvements in cognition. While practice at any task should lead to some form of improvement for that specific task, it is not clear that this improvement reflects anything other than a basic learned process for that specific task."

A Nintendo spokesperson said: "The Brain Training ... software is inspired by the theories of Japanese neuroscientist Ryuta Kawashima, who believes the brain can benefit from a daily workout, just as you would work out a muscle in the body.

"Nintendo is very careful to ensure the Brain Training products make no health claims directly related to the software. All [TV] advertising is ... approved by the BACC to further ensure it does not make misleading claims."

· Sense About Science is an independent charity set up in 2002 by the Liberal peer Dick Taverne to promote "good science and evidence in public debates". It encourages scientists to engage in controversial issues such as GM foods or animal research, and it aims to respond to inaccuracies in public claims about science, medicine and technology while promoting the benefits of research. The charity is governed by trustees, who include journalists, doctors and scientists. It is funded by donations from other trusts and foundations, and societies, industry and individuals.