In "Understanding and Managing Your Child's Food Allergies(2006)," by Scott H. Sicherer, M.D., I learned that sesame and poppy seeds seem to cause severe allergic reactions for some. Seeds such as sunflower and flax seed have varying amounts of proteins, and the amount of seeds eaten can make a difference as to if a reaction develops. The author doesn't say how common this is or how likely. I believe I've seen sunflower seed on a list of "The 20 Least Allergenic Foods," on a couple of different internet sites. I've thought that sunflower seed and flax seed were quite safe to substitute in place of peanuts or tree nuts, and maybe they usually are, but it's good to know that they may be the problem, if I see my daughter eating a baked good I've made and she gets an unexplained rash. UPDATE Nov 2010- my daughter is just fine eating baked goods I've made with flaxseed. Sunflower seeds have been fine for her, but there was one particular brand that she developed a noticeable rash and hives- I think it was cross contamination issues with nuts. I have not bought sunflower seeds for her since, as her nut allergies are worse, and I don't want any that are packaged on the same equip as tree nuts.
Beef, says Sicherer(p. 66), may cause reactions if your child has cow's milk allergies, particularly if the beef isn't cooked well. About 10% of children with severe cow's milk allergies react to beef. This is because beef retains some cow's milk proteins. Another thing to keep in mind if my daughter is eating beef and I notice a rash. (I sometimes notice rashes on her face and am frustrated, thinking, what was it that she ate that she's reacting to?!")UPDATE Nov 2010: I haven't had issues with my daughter eating beef. I have since realized that even her being around her allergens and touching, then ingesting, she can get a rash.