Gradual Egg-tolerance Induction in Hen's Egg Allergic Children

1. The investigators here want to test the hypothesis that a total period of 18 months of gradual open introduction of a certain egg product with regard to full egg tolerance induction is not inferior when compared to a total period of 30 months gradual open introduction of a certain egg product (see steps for the specific egg products) after tolerance to baked egg has been obtained.
2. The investigators also want to define step-specific 'tolerance-failures' and study the relevance of specific IgE to specific egg components to predict failures at each step.

Step 1: open baked egg test passed (either at home or in the hospital): this is routine clinical practice; afterwards daily intake of increasing amounts of heated egg (amounts to be noted in diary)

Step 2: open provocation test at home with hard-boiled egg, both hen's egg white and yolk, passed; afterwards weekly intake of either hard-boiled egg white or yolk or both (amounts and days to be noted in diary)

Step 3: open provocation test at home with waffles, omelet, pan cake or scrambled egg passed; afterwards weekly or two-weekly intake of one of these specific preparation forms or of the previous preparation forms (amounts, days and preparation to be noted in diary)

Step 4: open provocation test at home with fried or poached egg or softly boiled egg with liquid yolk; afterwards regular intake of one of these preparation forms or one of the prior steps (amounts, days and preparation to be noted in diary)

Step 5: open provocation test at home with raw egg: eg. In chocolate mousse; mayonnaise or tiramisu; afterwards unlimited intake of all egg containing preparation forms (for 3 months in both groups to be noted in the diary)

If tolerance to a certain step is not yet present (this is: if any reaction occurred during the months registered between two steps), the next step will be postponed. The number of failures (any reaction in relation to egg ingestion), the type of reaction and the additional time period necessary before the next step can be taken, will be recorded. After each time period, the investigators will measure specific IgE to hen's egg white and to Gal d 1, as standard clinical practice.