About 10 years ago some infernal, multilegged creature crawled deep into my ear. I poured water into the ear to flush the critter out. I was about to crack when an ant scurried out. Perhaps most interesting is that itching reflects our thoughts and emotions. Some people become itchy when they're anxious or depressed.
Some people scratch their heads when they're deep in thought.
Ark. It seems that everything causes itching. Skin disorders, obviously, are a major culprit. Acne can itch. So can scars. Various bacterial, fungal and viral infections also cause itching.