Scientists have found a gene defect which can triple the risk of a child developing a peanut allergy.
It could lead to new treatments for the most common cause of death from food aversions.
An international team, led by researchers at the University of Dundee, studied defects in the Filaggrin protein, which are carried by more than 10 per cent of people.
Previous studies showed this defect caused a range of other allergic conditions including eczema and asthma.
Dr Sara Brown, of Dundee, said: 'It was a logical next step to investigate whether Filaggrin may also be a cause of peanut allergy, since a child may develop all three of these diseases together.
'Allergic conditions often run in families, which tells us that inherited genetic factors are important. In addition to that, changes in the environment and our exposure to peanuts are thought to have been responsible for the recent increase in peanut allergy seen in the Western world in particular.
'Now, for the first time, we have a genetic change that can be firmly linked to peanut allergy.'
The Filaggrin gene helps build barriers in the skin to protect the body against irritants and allergens.
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Changes in the gene decrease the effectiveness of this barrier, allowing substances to enter the body and leading to a range of allergies.
The study found that one in five of all peanut allergy sufferers has a Filaggrin defect. Those with the defect can be three times more likely to suffer peanut allergy than people with normal Filaggrin.
The collaboration looked at 1,300 people in four different population groups in Canada, England, Ireland and the Netherlands.
Scientists said it was the first time that any genetic association with peanut allergy has been demonstrated in more than one population, making it more likely to be a 'genuine risk factor'.
Professor Irwin McLean, one of the world's leading authorities on Filaggrin who is also based at Dundee, said: 'The Filaggrin defect is not the cause of peanut allergy but we have established it as a factor in many cases. We don't yet know enough about the causes of peanut allergy but this is an important step forward.'
The findings are published today in the Journal of Allergy and Clinical Immunology.