The main difference between an allergy and a sensitivity lies in the immune system's response and the severity of symptoms. When someone with an allergy encounters the allergen, their immune system overreacts, producing antibodies (IgE) that trigger symptoms such as hives, itching, swelling, difficulty breathing, or anaphylaxis. Allergic reactions can be immediate and severe. Sensitivity refers to a less severe reaction to a substance that does not involve the immune system. Unlike allergies, sensitivities do not typically cause anaphylaxis or involve IgE antibodies. Instead, sensitivities may cause digestive issues, headaches, skin problems, or other symptoms that vary in intensity and onset time.