It is a symptom of many systemic diseases, including diabetes, kidney failure, liver disease, Lyme disease, nerve disorders, thyroid disease and various forms of cancer. In some cases, itching is the first symptom of a serious internal illness. Diffuse, whole-body itching is an early symptom of kidney failure. In rare cases, a nasal itch heralds a brain tumor. Odd itches include aquagenic pruritus, which results from contact with water, and mitempfindungen, an itch in one spot on the body that results from scratching another spot.
Some itches are all in the mind.
Various mental conditions, from obsessive-compulsive disorders to delusional syndromes, compel people to scratch. And anxiety can make real itches worse. Despite the omnipresence of itching, scientists know relatively little about its physiology. So when you try to go to sleep, that itch that wasn't too bad during the day now becomes unbearable. The most important of these C-fiber neurotransmitters is substance P, which dilates blood vessels and indirectly activates mast cells.