If science has any credibility, it derives from transparency. When you make a claim about how something works, you provide references to experiments, describing what was done so it can be replicated, detailing what was measured and how. Then people discuss what they think it means in the real world.

Maria Hatzistefanis is a star of lifestyle pages and the owner of Rodial, the cosmetics company that sells a product called Boob Job which, it claims, will give you a "fuller bust" "increase the bust size" and "plump up the décolleté area" with "an instant lifting and firming effect", and deliver an increase of half a cup size in 56 days. Or rather an increase of "8.4%". It's all very precise.

I'm not going to lose sleep over anybody who buys a magic cream to make their breasts grow bigger. What worries me is that Hatzistefanis's company is making libel threats against a doctor, simply for daring to voice doubts at these claims.

This is her crime. Dr Dalia Nield, a plastic surgeon, told the Daily Mail it was "highly unlikely" the cream would make your breasts bigger, and questioned the amount of information provided by Rodial. "The manufacturers are not giving us any information on tests they have carried out. They are not telling us the exact ingredients in the product and how they increase the size of the breast."

That's fair. I don't trust claims without evidence, especially not about a magic cream that makes your breasts expand. Maybe it does work – I don't particularly care, either way – but when I asked the company for any evidence or information on ingredients, they refused. This is odd, as I've seen the letter Rodial's lawyers sent, and they tell Dr Nield: "Our client on request would have provided all information required on clinical assessment and product ingredients."

Apparently not.

Dr Nield went on to speculate that the gel could be "potentially dangerous … it may even harm the skin and the breasts – we need a full analysis". This is reasonable: anything that has real effects on the body may have unintended side-effects, and that is an uncontroversial statement, especially when important information is being withheld.

The story gets stranger. When Sense About Science, who have helped drive the campaign for libel law reform in the UK, put out a press release about Rodial threatening Dr Nield with libel, they were contacted by Hegarty, the firm of solicitors for Rodial. They seemed to be trying to stop people from daring to talk about the existence of their libel threat.

People often ask if there are short cuts in detecting nonsense. It's not easy to do in a checklist, because there are so many ways to distort evidence, but for me there is one clear risk factor. Science is built on transparency, giving your evidence and engaging with legitimate criticism. If you hear of a company refusing to hand over evidence it says supports its claims, whether they are a drug company or some dismal cosmetics firm, all you know is that you are being deprived of information and that vital parts of the picture are missing. If you hear someone is threatening to sue their critics, again, all you know is that people will be intimidated from raising legitimate concerns and, again, you are being deprived of information.

Meanwhile, Dr Nield is one individual facing a large company. Doctors and scientists are commonly asked for their opinion on medical interventions, and it's in our collective interest that they give honest answers without fear that their lives will be taken over for years by a company with money and a distorted sense of reputation, and lose vast sums of money even if they successfully defend the case, as has happened so many times recently. With the law today, doctors and scientists might be wise to stop giving any view about any drug or health-related product marketed for commercial purposes, in any forum, and make it clear that from now on, decisions about efficacy should be made solely by the manufacturers. Good luck with that.