5–8% of the population suffers from a food allergy that can potentially lead to a severe reaction. Different factors of severity have been studied, but the relationship between the amount of allergen consumed and the severity of the reaction has never been investigated. Therefore, there is uncertainty regarding the consumption of very small amounts of allergen (traces).

The aim of our study was to analyze qualitatively and quantitatively the allergen content in foods that have caused a food allergy reaction.

We collected during one year (2021) medical history, food samples eliciting reactions and allergy diagnostic tests of patients presenting reactions suggestive with immediate food allergy and consulting in the emergency departments in the University Hospitals of Geneva and local hospitals or in the allergology outpatient consultation. The samples were analyzed by immunoassays and mass spectrometry.

In total, we recruited 145 patients, 105 (72.4%) were children. Patients were mostly reacting to milk, egg, tree and peanuts. 30% of the reactions were severe reactions needing epipen. When analyzing the foods, we found in the 115 food samples analyzed so far eliciting doses from 12.8mg/kg to 1000g/kg of food.

In this non-exhaustive series of food allergic reaction over one year in the canton of Geneva, we higlighted that (1) there is no general relationship between severity and quantity of allergen consumed, (2) “trace” declaration on foodstuff does not reflect the quantity of allergen in the foodstuff and doesn’t provide the necessary information for allergic patient. In conclusion, results for this study will help to provide better counselling for prevention of accidental reactions, in particular in children.