Egg allergic patients may tolerate some foods with eggs, but not others - why?

The egg allergen is affected by the degree of heating. Therefore, there are patients who tolerate cakes and muffins but still react to pancakes, French toast, and scrambled eggs.

Both mayonnaise and ranch dressing contain egg that has been pasteurized but is still more allergenic than egg that has been more extensively heated. Therefore, a challenge would be needed to determine if the patient who is tolerating muffins or pancakes can tolerate products with egg that has been less extensively heated.

Who will "outgrow" food allergy? It depends on the epitope

Each food is composed of many proteins and these proteins have multiple areas, termed epitopes, to which the immune system can respond. Epitopes that are dependent upon the folding of the proteins are called conformational epitopes. Epitopes that are not dependent upon folding are called linear epitopes.

A linear epitope oftens means a more prolonged allergy which is “stable” and persistent. A conformational epitope (egg, milk) often means a mild, transient allergy.



8 top allergens account for 90% of food allergies (click to enlarge the image). The likelihood of a negative oral food challenge is shown in relation to the respective values of skin prick test (SPT) and serum IgE (sIgE).

References:

If patient tolerates egg baked in pancakes and muffins should they be able to tolerate in mayonnaise and ranch dressing? AAAAI, 2011.
Ovomucoid- and ovalbumin-specific IgE/IgG(4) ratios  predict reactivity to baked egg. JACI, 2012.
Rare, medium, or well done? Effect of heating on food protein allergenicity http://goo.gl/Z4LbX - It definitely affects milk and egg products.

Image source: Wikipedia, public domain.