Especially in the case of dairy, there’s frequently a confusion over the difference between intolerance and a true allergy. The big difference: Immune response.
In a food allergy, the immune system treats a food product as a foreign invader in the same way it would for someone with a ragweed or dust allergy. The body produces Immunoglobin E (IgE) antibodies specific to the allergen. The next time a person comes in contact with the allergen, the IgE antibodies trigger an allergic response. Depending on the severity of the allergy, symptoms might range from sneezing and itching to hives, difficulty breathing, and anaphylaxis.
A food intolerance is sometimes referred to as a non-allergenic food hypersensitivity. It presents its symptoms more slowly and can appear as a chronic ailment affecting skin, respiratory tract, or gastrointestinal tract. It can be difficult to diagnose or pinpoint the cause. The good news is that while rashes, headaches, congestion, nausea and diarrhea are uncomfortable, food intolerance is extremely unlikely to be fatal.