Inquiry

Science

fascinating itchiness feedback loop:
histamine → stimulates sensory nerves → neuropeptides released → activate mast cells → histamine released

histamine acting in skin and in the brain produce different effects. first-generation antihistamines (like Benadryl) are a non-selective H1 receptor antagonist that crosses the BBB and blocks both peripheral and central H1 receptors, which causes drowsiness via the CNS; whereas second-generation antihistamines (like Zyrtec) do not cross the BBB and bind peripheral H1 receptors primarily, largely avoiding effects to the CNS.