Allergic reactions are primarily caused by which of the following?

Allergic reactions are primarily caused by proteins, specifically allergens, which can provoke an immune response in sensitive individuals. When a person is exposed to a particular allergen, which is often a protein or proteinaceous component from substances like pollen, pet dander, certain foods, or insect stings, their immune system mistakenly identifies it as a threat. This triggers the production of immunoglobulin E (IgE) antibodies, leading to a cascade of immune responses.

Histamines play a significant role once an allergic reaction is initiated. They are released by mast cells and basophils in response to the binding of IgE to the allergen. The release of histamines leads to various allergic symptoms, such as sneezing, itching, and swelling; however, histamines themselves are not the primary cause of the allergic reaction.

Enzymes and neurotransmitters, while important in many biological processes, do not primarily drive allergic reactions in the same way proteins do. They may have roles in other bodily functions, but they are not the main instigators of the immune response associated with allergies.