snorkie, thats nearly right, but can be wrong as well!
skin exposure can be a cause, but for most of todays allergic infants, it can start before birth, the ability to develop a imume system just waiting to find a trigger.
my typical allergic march child has always reacted to his allergens at first exposure, touch for nuts, and instant at first taste to many others.
he is allergic to tree pollen, mainly because he was a spring baby, he is allergic to dustmite, something he was exposed to at birth.
the tree pollen leads on to his kiwi allergy, and his peanut, springs forth his allergy to other legumes.
his tree pollen alleryy did cause hay fever , but now outgrown.
his egg allergy often goes hand in hand with peanut, something to do with similar protein strands.
was exposed to dog at birth, on other peoples clothes who owned dogs, and when in same room that a dog had been in.
severe allergy to dogs, and cats.
and so on and on and on.
so , no, wouldnt say that its always safely eaten at first all the time.
however for adults and older children, allergies can develop out of the blue.
a immune system changing, (think teens and all that change!) for those woman going through the menopause, shellfish allergies seem to be a common thread.........
allergies are a complete pain, thats the only constant in it all.