Immediate and Delayed Food Allergy: When Do Symptoms Appear?
- Why does a food allergic reaction occur?
A food allergic reaction occurs because proteins, that are present in foods we eat, are erroneously recognised as “dangerous” by our immune system, which normally protects us from infectious agents. Thus, after having recognized the allergenic protein, the immune system triggers an immune response to neutralize the dangerous protein: this is the allergic reaction.
- Do allergic reactions always show up immediately after the ingestion of the allergenic food?
There are essentially two types of allergic reactions to foods, one showing up immediately after the food ingestion (the immediate on-set reactions), the other showing up later, even after 2 days from the ingestion of the allergenic food (delayed on-set reactions).
- Are immediate and delayed on-set food allergic reactions different?
Broadly speaking, yes. Immediate on-set allergic reactions involve IgE antibodies, while delayed on-set food allergic reactions engage other components of the immune system, the T-cells.
Immediate on-set allergic reaction
The IgE-Mediated Food Allergy | Delayed on-set allergic reaction
Non-IgE-Mediated Food Allergy |
The parts of the immune system responsible for immediate on-set food allergic reactions (the most dramatic example of which is food anaphylaxis) are IgE antibodies.
In food allergic people (who are sometimes referred to as being “atopic”) eating certain food proteins (such as whey and casein protein contained in cow's milk) results in the production of specific IgE antibody molecules directed against the protein. The second time the individual eats the food, these specific IgE molecules interact with each other and with the protein, to cause the release of harmful chemicals (such as histamine) from mast cells, causing damages associated with the symptoms of food allergy.
Damage may occur to the skin, respiratory system or gastrointestinal tract.
The audiovideo explains the immune system responsible for immediate on-set food allergy
| “T-cells” are the components of the immune system responsible for delayed-type food allergic reactions.
In people with a predisposition for delayed on-set food allergy, initial ingestion of food protein leads to the production of specific types of “T-cell”. When the food is subsequently ingested, the food protein is “processed” in a variety of ways and “presented” to the previously generated food-specific T-cells. These T-cells then “invade” the area of the body about to suffer damage (e.g. skin, bowel).
This processing, presenting and invasion can take up to 24-48 hours, which explains the delayed response. T-cells release chemicals that, through a chain of events, lead to the damage associated with symptoms of food allergy.
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