What is the mechanism of action for antihistamines?

Antihistamines work primarily by binding to histamine receptors, specifically the H1 receptors, on cells rather than stimulating histamine release. When histamine is released during an allergic reaction, it binds to these receptors and causes symptoms such as itching, swelling, and vasodilation. By occupying these receptors, antihistamines prevent histamine from exerting its effects, thereby alleviating the symptoms associated with allergic reactions, such as sneezing and itching. This interaction is crucial for their efficacy in counteracting the effects of histamine in the body.

The other options do not accurately describe how antihistamines function. For instance, stimulating histamine release would exacerbate allergy symptoms rather than alleviate them. The notion that antihistamines cause vasodilation is misleading; instead, they inhibit the inflammation and excessive dilation induced by histamine. Lastly, increasing white blood cell counts is not related to the action of antihistamines, as they primarily target specific receptors associated with allergic responses rather than affecting overall immune cell production.