This can result in symptoms that mimic an allergic reaction. It can occur due to genetic factors or certain medications. Histamine is a signaling molecule, which means it sends signals between cells.

Allergy season can be miserable for tens of millions of Americans when trees, grass, and other pollens cause runny noses, ...

H1 blockers like Zyrtec (cetirizine) block receptors from an immune response are typically used to treat environmental or seasonal allergy symptoms. H2 blockers like Pepcid AC (famotidine ...