Experiment 042 was the 42nd genetic experiment created by Jumba with Hämsterviel's funding. He was designed to make you extremely itchy.
042 and the other first 624 experiments were deactivated and smuggled to Earth by Jumba during his mission to capture Experiment 626.
All of the experiment pods were released and scattered across the island of Kauai.
At an unknown point, Itch was persumbably activated, tamed, and named Itch.
Itch is a teal mammalian flea-like experiment.