Raw Egg is More Allergenic Than Cooked or Processed Egg
Yes, raw whole egg is more allergenic than cooked or processed forms, and this has critical implications for oral food challenges and dietary reintroduction in egg-allergic patients. 1
Evidence from Clinical Guidelines
The Journal of Allergy and Clinical Immunology guidelines explicitly state that "raw forms of foods are more allergenic than processed/cooked versions of foods" and specifically use hard-boiled egg as an example. 1 This principle is so important that the guidelines mandate: if an oral food challenge is performed with cooked egg (such as hard-boiled egg) and the patient passes, only similarly processed/cooked versions of egg may be added to the patient's diet—not raw egg. 1
Clinical Implications for Practice
Oral Food Challenge Protocol
- When performing oral food challenges, use the least processed/cooked form of food that will actually be incorporated into the patient's diet. 1
- Standard challenge portions include 1 hard-boiled or scrambled egg, or 1 slice of French toast (containing 1 egg per slice of bread). 1
- A negative challenge to cooked egg does not grant permission to consume raw egg products. 1
Mechanism of Reduced Allergenicity with Heating
The reduction in allergenicity with cooking relates to the differential heat stability of egg proteins:
- Ovomucoid is the most heat-stable egg allergen and remains allergenic even after extensive heating. 2
- Patients who react to heated egg typically have higher IgE antibody levels to ovomucoid compared to those who tolerate heated egg. 2
- In one study, 21 of 38 subjects (55%) who reacted to freeze-dried raw egg white had negative challenge responses to heated egg white, demonstrating substantial reduction in allergenicity with heating. 2
- Heating combined with ovomucoid depletion resulted in 16 of 17 subjects (94%) who reacted to heated egg white having no reaction to heated and ovomucoid-depleted egg white. 2
Protein Structure and Digestibility
- Egg proteins' allergenicity is linked to their resistance to gastroduodenal digestion, which allows them to reach the intestinal mucosa intact and trigger immune responses. 3
- Processing and heating alter protein structure and digestibility patterns, generally reducing allergenic potential. 3
- Pasteurized whole raw egg powder maintains similar IgE-binding patterns to fresh raw egg, making it a suitable substitute for raw egg in clinical challenges when infection risk is a concern. 4
Major Egg Allergens
The four primary egg white allergens are: 5
- Ovomucoid (most heat-stable)
- Ovalbumin
- Ovotransferrin
- Lysozyme
Ovomucoid plays the most important role in allergic reactions to egg white compared to other egg proteins. 2
Common Pitfall to Avoid
Never assume that tolerance to baked or cooked egg means tolerance to all egg forms. 1 This is a critical safety issue—patients who pass challenges with extensively heated egg (such as in baked goods) may still react to lightly cooked or raw egg preparations. The degree of heating and processing directly correlates with allergenicity reduction. 2, 3