Final answer:
In allergic reactions, excessive amounts of histamines are produced by mast cells which can lead to various symptoms, and antihistamines are commonly used treatments.
Step-by-step explanation:
When an individual is hypersensitive or allergic to a specific thing, excessive amounts of histamines are produced. Histamines play a central role in allergic reactions and are compounds released by mast cells in response to allergens. On initial exposure to an allergen, the body synthesizes IgE antibodies that bind to mast cells. Upon subsequent exposure, these sensitized cells release histamine and other inflammatory mediators. This release can cause various symptoms ranging from mild reactions like sneezing to severe anaphylactic shocks. Treatments for allergies often involve antihistamines or other medications like steroids.