Welcome to the forum.
Allergic reactions occur instantaneously upon exposure to an allergen or ingestion.
Read the book ( public domain-free download) Dr. Coca's Pulse Test.
You will then have a better understanding. There are many types of allergies, reactions
and sensitivities. Sometimes the symptoms may not show for quite some time
and sometimes they show up right away.
However, the reaction in the body takes place immediately, whether we experience symptoms or not.
And unfortunately many people are suffering from serious illnesses-some for life- because of undetected and undiagnosed allergies.
Should you have a particular situation, please post with more details.
Hi, welcome to the forum, food allergy may start any time after allergen containing food is taken and there is no fix timing. It usually starts within one hour after intake of food.
Determination of the food you are allergic to, is one of the challenges which you need to pass through.
The common existing food allergens are Peanut flour, peanut butter, powdered egg white, Powdered/fresh milk Soy milk, soy flour Wheat breads, flour etc.
As allergic reactions are IgE mediated, blood tests will show increase in these levels secondary to a food allergy. The problem with the food allergy testing is sometimes the amount of food they challenge with may be not sufficient to elicit any allergic reactions.
When such food is consumed in large quantities can elicit allergic reaction in the form of hives, redness of skin, itching etc. You need to note down such food also in your diary and avoid the intake in future.
I suggest you to consult skin specialist/ immunologist for further line of management. Take care and regards.