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Are there any foods that can cause sudden food allergies?

No food can cause an allergic reaction the first time it's ingested. The way an allergy works is that the first time you eat a food, if your immune system decides that food is dangerous to your body, it produces antibodies to "protect" you from the food. Then the next time you eat the food, these IgE antibody molecules interact with the proteins in the food and with each other, causing harmful chemicals such has histamine to be released and cause your allergy symptoms.

When this happens you have a Type I or immediate-onset allergic reaction, meaning you feel the symptoms within two hours of coming into contact with the food allergen. Symptoms may range from a rash or hives to vomiting, trouble breathing or even anaphylactic shock, which is life threatening. There are no specific foods that are more likely to cause Type I reactions than Type II, III or IV reactions. Type I reactions are generally more dangerous and easier to diagnose than the other types. The speed and severity of your reaction depends on a number of factors: how much of the allergen you consumed, how it was prepared, what else you ate with it, how sensitive you are to it, and other medical problems you may have.

Severe immediate allergic reactions are most common with tree nuts, peanuts, soy and wheat. In addition, milk and egg allergies are among the most common in children, and fish, shellfish and citrus allergies are among the most common in adults. Anyone of any age can have a sudden allergic reaction, even to a food that hasn't been problematic for him or her in the past.