system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:What exactly is an itch? What triggers us to feel like we need to scratch that spot?

and I don't just mean insect bites, but also when we get those random itches??
gpt
An itch is caused by a molecule (Neuropeptide Natriuretic Polypeptide B) that is released by a nerve cell which triggers a system in our bodies telling the brain that you have an irritation on some area of your skin. Sometimes the nerves are stimulated by an actual itch and sometimes they are stimulated by reactions to chemicals in our bodies (like Histamine). It's really hard to say exactly what causes itches but scientists are working on pinpointing the exact reasons.