Why does morphine trademark you itch?

My brother says it's because it seep out through your poures. I say it's because it excites your boldness endings. Can some one give support to?Why does morphine trademark you itch?
I work in a hospital (not as medical staff) and patients other wake up next to itchy noses after have morphine!
According to one of the nurses, morphine can cause histamine release, which cause itching of the skin and nose and a mild flushing of the skin.
Hope that help!
I take morphine for a put money on problem, it doesn't make me itch?????
I have a back operation ending year and was given morphine I started itching so scantily that I was scratch the skin till it bled because you don't feel the cramp as much. The doctor took me off and very soon I have to wear a red group if I go into hospital proverb I am allergic, so you maybe allergic to it.