Study to Assess Tolerance of Traces in Peanut/Tree Nut Allergic Children.

This protocol will help better define whether patients with peanut and/or tree nut food allergy can tolerate traces in products with precautionary allergen labelling.

Visit 1 (V1): During this visit at the Pediatric Research Platform at the Children's Hospital, subjects will undergo an open food challenge to 3 processed foods labeled with "may contain traces" by following safety and accuracy guidelines for food challenges (7). The following foods (similar for all patients) will be given in one dose in the size of a regular serving:

* cookies, max 30 g;
* chocolate, max 30 g;
* breakfast cereals, max 50 g.

Each meal will be administered with a 1 hour observation period in between and at the end.

If the patient does not react to any of the foods or has only oral itching (mild symptoms), he/she will be instructed to stop the ban on "may contain" foods and eat them regularly. If the patient has more than mild symptoms, the study will be stopped and the patient will be banned from eating foods with traces. The study subjects with a negative challenge and instructed to eat foods with the "may contain" label will be provided emergency medications and instruction on when and how to use them according to current guidelines (8).

An age appropriate quality of life questionnaire will be filled out by the parents/patient during the visit.

For the following 3 months after "may contain food" challenges, the patients will be invited to eat on a regular basis any foods labeled as "may contain" tree nuts and/or peanuts and record the consumption on a diary. Such foods will only be eaten in presence of a family member instructed for the measures to be taken in case of a reaction. They will record any history of reaction and contact the study team. The brand name of the food, and if available the batch will be recorded. The participants will store the study food and its packaging safely in a box and bring it along at V2 for allergen content analysis.

If a reaction occurs, the food will be analyzed for allergen content by immunoaffinity capillary elecrophoresis-matrix assisted laser desorption/ionization mass spectrometry, as well as a simplified version of this technique, the immunomagnetic separation -matrix-assisted laser desorption/ionization mass spectrometry.

Visit 2 (V2): During this visit, the parents/patients will report on the brand, the frequency and the amount of "may contain" foods eaten since V1.

The quality of life questionnaire will be filled out again by the parents/patient.

Eligibility Criteria:
Inclusion Criteria:

* Children aged 2-18 years at time of inclusion
* Tree nut or peanut allergy documented by:

  * Positive skin prick tests (SPTs) to peanut and/or tree nuts
  * Positive specific IgE (sIgE) to peanut and/or tree nuts ( ≥0.35 kU/L)
  * A recent (\< 1 year) positive food challenge, reacting to the dose of 30 mg of proteins or below.
* Parent/Legal guardian has been informed about the study and has signed Informed Consent Form

Exclusion Criteria:

* History of a moderate or severe reaction during a food challenge with a dose of 30 mg of proteins or less.
* Expected non-adherence to the study protocol.
* Severe or uncontrolled asthma.