Dry roasted peanuts may be more likely to trigger allergic reactions than those that are "raw", a study has shown.
The high temperatures involved in dry roasting cause chemical changes that can sensitise the immune system to peanut proteins, research suggests.
Scientists believe this may explain why peanut allergy is so much more common in the West than in eastern Asia.
Dry roasted peanuts are a popular snack in Western countries, whereas in the East they are more often used in cooking and eaten raw, boiled or fried.
The research involved comparing the effects of proteins from dry roasted and raw peanuts in mice. Animals initially exposed to dry roasted peanut proteins subsequently developed a far stronger immune reaction to peanuts. Dr Amin Moghaddam, from Oxford University, said: "Our results in mice suggest that dry roasted peanuts may be more likely to lead to peanut allergy than raw peanuts.
"The dry roasting causes a chemical modification of peanut proteins that appears to activate the immune system against future exposure to peanuts.
Professor Quentin Sattentau, who led the team from Oxford University's Dunn School of Pathology, said: "This is the first time, to our knowledge, that a potential trigger for peanut allergy has been directly shown."
But he stressed that the research was at an early stage and it would be premature to avoid roasted peanuts or their products.