People with a peanut allergy are more at risk of a reaction if they exercise or suffer from sleep deprivation, research has shown.
The find could pave the way to a new understanding of when allergic reactions are more likely to strike.
One in every 100 adults and one in every 50 children have peanut allergies - the most common cause of fatal allergic reactions.
Both exercise and sleep deprivation reduce the "threshold of reactivity" - the amount of peanut needed to trigger a reaction, the allergy research team at Addenbrooke's Hospital found.
The study, funded by the Food Standards Agency (FSA) and published in the Journal of Allergy and Clinical Immunology, will be used in work around food labelling, the FSA said.
Dr Shelley Dua, lead investigator at Addenbrooke's, said: "Precautionary allergen labels on food such as the commonly used 'May contain traces of...' are currently quite vague and not very helpful.
"This is partly because until now we simply haven't known enough about the amount of allergen which causes a reaction and how day-to-day factors like tiredness and exercise affect allergic reactions.
"This study takes us a long way towards building that knowledge and changing the way we label allergens, making life easier and safer for allergic individuals."
FSA chairwoman Heather Hancock said: "The FSA commissioned and funded this groundbreaking research because we want to significantly improve the understanding of everyday impacts that can contribute to an allergic reaction.
"This is vital work and can help us redefine how foods are labelled in future, so that people can manage their allergies more safely.
"It's impossible to remove the allergy risk for people, but these findings give us essential evidence. In future, it could support precautionary allergen labelling so people will know exactly when a food poses a real risk to them, which can increase the trust they have in their food."