We’re not talking about itches from bug bites or poison ivy, which are reactions to histamine. We mean those random itches that leave you absent-mindedly scratching your nose.
Itch research remains a relatively new field of study, and, previously, itches were thought to be just extremely mild forms of pain. While both itches and pain (and heat) are all transmitted through the body by similar neurons, a 2013 study showed that itches are special—they’re triggered by Nppb, a neurotransmitter that also happens to be responsible for controlling blood pressure. Without Nppb, you wouldn’t feel itchy.
Gil Yosipovitch, M.D., director of the Temple Itch Center, explains that itches evolved to warn animals of environmental dangers. Receptors near the skin’s surface are poised to react to any external irritant, no matter how tiny. If you feel a random itch, something just a couple microns long—be it dust, soap residue, dead skin, or a thread of clothing—is probably disturbing a few nerve endings, which send signals to the spinal cord asking for a much-needed scratch.