A food allergy is a mistake made by the immune system. The body treats a harmless protein in a food as though it were something dangerous, and mounts a defence against it. The food has not changed. The response to it has.
An allergy is not a preference, a fad, or a fussy eater being difficult. Nobody chooses one and nobody is talked out of one. The reaction happens whether the person wants it to or not, and wanting very much to be well has no effect on it at all.
An intolerance is a different thing. It is usually the digestive system struggling with a food rather than the immune system attacking it, and while it can make somebody thoroughly miserable, it does not carry the same risk. Both are real, both deserve to be taken seriously, and the two need different handling.
Nobody has settled the question of what causes allergies. Genetics play a part, so does the environment a child grows up in, and so does a great deal that is still being argued over in the research. What is clear is that no parent causes an allergy by feeding a child wrongly, and blaming one for it is both cruel and useless.
Allergies can develop at any age. Somebody who has eaten a food happily their whole adult life can begin reacting to it, and somebody who reacted as a toddler may not react as a teenager. That second direction is what people mean by outgrow, and it is not something to assume has happened without testing.
Severity is not fixed either. The size of a past reaction is a poor predictor of the size of the next one, which is why an allergic person whose last reaction was mild is still taking a real risk. That unpredictability is the whole reason allergic families ask so many questions.
Cooking does not remove or neutralise allergen proteins — and where a doctor has told a particular family something different about a particular food, the doctor is right about that family and this page is not. Heat changes flavour and texture; it does not make the protein invisible to an immune system that has decided to attack it. Neither does freezing, and neither does stirring a small amount of the food into something else.
Amount matters, but not in the way people hope. For one allergic person a large helping is needed before anything happens; for another a smear left on a plate is enough. There is no threshold that holds across people, which is why nobody can borrow anybody else's answer.
Everything on this page is general education about allergies. It is not a diagnosis and it cannot become one: nothing on a website can work out what a particular person's body does with a particular food. That is a question for a doctor who can actually test for it.
Questions this page raises
Ezzie will have a go at any of these.