Sometimes, you know exactly why you’re itchy: you have a mosquito bite, you had a run-in with some poison ivy, your allergies or eczema is acting up. But you know when you have an itch that seems to come from nowhere? You find yourself mindlessly scratching at the back of your hand, or your back suddenly breaks out in an outrageous itch and you can’t reach it. Why on earth does this happen?
There was a time when itches were considered a mild subset of pain – the study of itching is pretty new in the scientific and medical communities. It’s true that pain and itches, as well as heat, share very similar neural pathways and excite the same neurons. But a study from 2013 shed some new insight onto how itches differ from pain. Itches are related to a neurotransmitter known as NPPB (don’t worry about trying to pronounce that, it’s an abbreviation for natriuretic peptide B). NPPB, interestingly enough, is also a major player in blood pressure control; it’s also the sole cause of itchy sensations in your body.
Itching has an evolutionary benefit, according to Gil Yosipovitch of the Temple Itch Center; itches can warn us of dangers in our immediate environment, such as poison or miniscule irritants. The receptors on our skin’s surface are constantly analyzing and responding to external stimuli, and when danger is sensed there are a number of possible reactions including pain, heat, and itches. Something as small as a single thread, or as innocuous as soap residue or your own dead skin, can ignite your nerve endings and make you crazy to scratch that itch.