US experts have said that full-body scanners now being introduced at some international airports are unlikely to increase an individual’s risk of developing cancer in the future.

A report by Reuters quoted US radiation expert Dr James Thrall from the American College of Radiology as saying that radiation thresholds of the scanners were ‘well below’ levels that would pose a cancer risk. Dr Thrall is also chief of radiology at Massachusetts General Hospital in Boston.

‘When X-rays are used for medical imaging purposes, they have to be energetic enough to get through the human body,’ said Dr Thrall.

‘The X-rays used in the backscatter machines in airports have such low energy that they literally bounce off the skin. That is what backscatter implies.’

Airports in the Netherlands, Canada and the UK are introducing full-body scanners following the failed attack on a flight to Detroit on Christmas Day.

The machines have been criticised for their intrusiveness – and some UK experts say they contravene child protection laws.

Airports use two types of X-ray machine to scan passengers – millimetre wavelength imaging equipment aims radio waves at the body to create a three-dimensional image, while backscatter machines harness low levels of radiation to create a two-sided image. Both types of scanner can see through clothes and pick up any unusual items a person might be carrying. However the backscatter machines use ionizing radiation used in medical X-rays.

‘All of the concerns that we have about the medical use of X-rays really don't apply to these devices,’ said Dr Thrall. ‘The exposure is extremely low and the energy of the X-rays is also very, very low.’

The US already has 40 millimetre wave scanners situated at 19 airports. The US Transportation Security Administration says that a single scan by a backscatter machine is equivalent to two minutes of flight time in terms of radiation dosage.

David Brenner, who is director of the Centre for Radiological Research at Columbia University Medical Centre in the US, said it was a matter of weighing up the risks of radiation against the benefits of being scanned in this way to prevent terrorist attacks on aircraft.

‘From an individual's point of view, the risks are going to be small,’ he said. ‘If very large numbers of people would be exposed to a small risk, then you've got a population problem.

‘If the benefit means we're safer, then that probably outweighs the potential risk,’ he added.

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