Why am I itching???????

[Dianyla]

Histamine can bind to a number of different histamine receptors - H1 and H2 are the prominent ones that the drugs tend to target, but there are H3 and H4 receptors as well. Heck, they may have found some others by now. What the histamine causes to happen, depends on what receptor it binds to. And the receptors are more prominent on different tissues.

Here's a neat map of histamine pathways in the body:

(click for bigger)