Parents have been warned against using allergy tests for their children bought online or on the high street because they are not scientifically valid.
Experts from the National Institute for Health and Clinical Excellence (NICE) said that parents should take their children to a GP if they are concerned about food allergies rather than spending money on often unreliable private tests.
The watchdog has drawn up new guidelines designed to make the process of diagnosing food allergies in children faster. It said that parents who buy private tests, many of which have no scientific basis, run the risk of unnecessarily restricting their child's diet, which could lead to them being undernourished.
Dr Adam Fox, a consultant in paediatric allergy at Guy's and St Thomas' Hospital in London, helped set out the new guidelines.
He said that the "skin prick" test used by the NHS for years is "absolutely scientifically validated".
But he said parents could get confused by the IgE blood test used on the NHS and some IgG food intolerance tests available commercially and often classed as alternative or complementary tests.
IgG could not be validated scientifically, Dr Fox said, adding that home testing kits, where the results are posted back to the company, should be avoided.
"You can't diagnose a child without seeing them," he said.
The guideline, aimed at those in primary care working with children and young people with suspected food allergy, says parents who opt for private allergy tests should ensure they are seeing a reputable, trained specialist.