My son will be 6 in May. He was diagnosed with allergies at 9 months. I fed him half a Yo Baby yogurt (so approx 2 oz) and he was covered in hives from head to toe, so swollen we could barely recognize him, and vomiting. He hasn't intentionally been fed a drop of dairy since. Allergy testing - both blood and skin tests - have also shown him to be allergic to eggs and most nuts.
Shortly before his 5th birthday, he finally tested negative to all tree nuts, though still positive to peanuts. He has never eaten a nut of any kind, so we don't know how, or if, he would react.
Around his 4th birthday, his egg test showed improvement, but upon feeding him eggs, he still reacted. Testing the following year showed further improvement. He can now eat baked goods (brownies, cake, cookies) with 1-2 eggs (but not 3) and he still cannot eat things like scrambled eggs, quiche, or anything else where the egg is not fully cooked into something. The process of baking denatures the protein that he is allergic to, so he can now tolerate it. When he does have a reaction to egg, it usually results in a small rash around his mouth and an itchy throat.
As for the dairy, even now he reacts with hives, vomiting and sometimes wheezing to even the slightest accidental exposure. One of his allergists said that on a scale of 1 - 100, a 15 is considered a severe dairy allergy. My son consistently tests at 100.
Prior to the formal diagnosis at 9 months, we had no idea he had any allergies. However, he did have bad eczema throughout his entire infancy and was nursed exclusively. I consumed dairy, eggs and nuts throughout my pregnancy and while nursing. It's highly likely that the eczema was a result of allergens being passed through my milk, but his old pediatrician never suggested it so we never knew.