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How does histamine help immune cells reach an injured or infected area?

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antihistamines, including Benadryl — antihistamine Antihistamines such as Benadryl (diphenhydramine) and Claritin (loratadine) can be purchased without prescriptions. Both of those agents act by blocking H₁ receptors. However, whereas Benadryl binds to those receptors in the central nervous system (CNS), causing drowsiness, Claritin does not readily enter the CNS and thus does not normally cause drowsiness.

When tissue is injured or infected, mast cells release histamine, which plays a vital role in the immune system response by facilitating inflammation.1

Histamine helps immune cells reach the affected area by causing nearby blood vessels to dilate and increase in permeability. This structural change allows leukocytes (white blood cells) and plasma proteins to leak out of the bloodstream and migrate through the vessel walls directly to the site of injury or infection. Once they arrive, these immune cells begin fighting the infection and working to nourish and heal the damaged tissue.1