How antihistamine works?
In: Biology
Allergic Rhinitis (or environmental allergies generally) is occurs when an allergen such as pollen (called an antigen) triggers a receptor on an immune call called a mast cell that tells the mast cell that it is bad for you. This mast cell releases a bunch of inflammatory mediators including histamine.
Histamine activates the histamine 1 receptor which causes your eyes to leak, your nose to run, itching, and your brain to tell your body to sneeze.
Antihistamines block this histamine 1 receptor to prevent this process from occurring when the allergen is encountered.
Additionally, histamine is one of the main wakefulness neurotransmitter. First generation antihistamines such as diphenhydramine, chlorpheniramine, doxylamine, and hydroxyzine enter your central nervous system and block receptors there as well, causing drowsiness. Second generation antihistamines such as cetirizine, loratadine, fexofenadine do not cross (or do so to a much lower extent) the blood brain barrier and thus are considered “non-drowsy”
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