It's complicated. There are so many kinds of allergies.
But, in short: many parents are needlessly restricting their kids' diets because of the fear of allergies, or the fear that the kids will develop allergies. As a result, I infer, some kids are growing up with unbalanced diets that can have knock-on effects on development.
The authors of the guidelines say that blood IgE tests for specific allergens are not, by themselves, enough to identify an allergy; nor are skin prick tests. Instead--as most of us already knew--the only true test is to eat the stuff and see if anything happens. And it's best if you eat the stuff in a double-blind trial in which neither the doctor nor the patient know, at the time, whether the patient is eating the candidate food or a placebo.
Alternatively, especially for non-IgE food allergies, you can drop a suspect food from your diet for a while and see if there are any changes. The authors recommend only dropping one or two foods at a time.
The authors make a number of intriguing points.
- Food allergies and eczema are highly associated; but you can develop tolerance to a food and it won't cause problems thereafter.
- Conversely, it's possible to become desensitized to a food if you eat a lot of it, but this desensitization can wear off. The authors only briefly touch on this point and don't list a reference.
- You can have a lot of IgE that binds a food, but not have an allergy. This is why blood IgE isn't so useful, and implies that there are other factors downstream of IgE that are altered in eczema patients: possibly a mast cell imbalance.
- You can have a non-immune reaction to food that can affect your quality of life. (E.g. lactose intolerance. I myself have reactions to aged cheese and pickles and concentrated tomato paste, which contain a lot of histamine; I have reactions to hot peppers and alcohol, which dilate blood vessels in my skin and somehow cause irritation.)
- Most kids will eventually tolerate all foods but tree nuts and peanuts.
- The authors do NOT recommend using allergen-specific immunotherapy to treat food allergies arising from IgE. I'm guessing this is because of the risk of anaphylactic shock. However, a large meta-study just found that sublingual immunotherapy was effective and virtually risk-free for treatment of hay fever. It must be that the allergens from pet dander, pollen, and dust mites are somehow less dangerous.
Drugs that alter the immune response to the allergen are commonly considered the most likely candidates for such therapy in the future, but these treatments are not currently recommended.I wonder whether there are any drug candidates in the pipeline.