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Allergy needs the immune system
The classic example is milk allergy versus milk intolerance. On the surface a mild milk allergy looks the same: an upset stomach, feeling gross, some gassiness. With intolerance, the body cannot digest lactose because it lacks an enzyme. With allergy, T cells and B cells produce antibodies that attack the milk protein.
An allergy can escalate. It can bring a skin rash, wheezing, and a full-on anaphylactic event that ends in the ER. Intolerance will not do that.
Mild forms of the two are easy to confuse, so many people assume they have an allergy, and the only way to know for certain is to see an allergist. There are only about 5,000 allergists in the US, compared with more than 40,000 anesthesiologists and 60,000 pediatricians. Seeing one takes a referral, so a lot of people are out there self-diagnosing.
What do T cells and B cells do in allergy?
B cells make antibodies, and in allergy they produce IgE aimed at a harmless substance. T cells help direct that process, with a subset called Th2 cells pushing B cells toward IgE production. IgE then attaches to mast cells throughout the skin, gut, and airways. On the next exposure, the allergen cross-links the IgE and the mast cells release histamine.
Why can milk allergy be dangerous but intolerance not?
Lactose intolerance is a shortage of lactase, the enzyme that splits milk sugar, so undigested lactose ferments in the gut. The effects stay in the digestive tract. A milk allergy involves the immune system reacting to proteins like casein and whey, and that reaction can spread to the skin, lungs, and blood pressure. This is why anaphylaxis occurs in allergy and not in intolerance.
Why are there so few allergists?
Allergy and immunology is a small subspecialty that requires training beyond a pediatric or internal medicine residency. The field has fewer than 6,000 practicing physicians in the United States, according to workforce surveys. Most of them cluster in metropolitan areas. Large parts of the country have no allergist within easy reach.
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