Though itching is a universal human affliction, science still cannot fully explain the exact mechanism by which we perceive an itch—or why scratching provides such fast relief. What we do know is that several chemicals produced by the body can cause itching, the most notorious being histamine. We also know that, though itching and pain sensations are carried by different nerve fibers, there must be interconnections. Very hot or cold applications, for example, can make an itch stop. And oral painkillers can often help relieve it. A study that scanned brain activity in people with deliberately induced itching found that when they were allowed to scratch, areas of their brains associated with unpleasant sensations, such as itching, became less active, while areas associated with pain became more so.
Itching is a symptom that can signal a near-limitless variety of problems, from trivial to life-threatening. If you have a persistent itch, here's how to proceed.
Itching can be generalized or limited to one or more specific locations. If the itch is localized and accompanied by a rash, here are the main culprits to investigate, in approximate order of likelihood:
With or without a rash, itches that have spread over your whole body sometimes indicate more serious conditions. Common causes include:
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