Itching helps us protect our skin. Scientists think that there are two kinds of itch and that each plays a different role. Like other feelings of the skin, itching is the result of signals carried by nerves from the skin to the brain.
The first kind of itch is caused by physical contact. This itch warns us when we touch a plant, insect, or chemical that might damage the skin. An opening in the skin can let in germs that cause infection. When we scratch or brush at the itch, we are trying to remove whatever caused it.
The second kind of itch is triggered by insect bites, allergies, or anything else that makes the skin release a chemical called histamine. The itch prompts us to scratch, which removes the outer layer of dead skin cells—along with any foreign objects or toxins that are stuck to them. Also, the irritation lets us know which plants and insects to avoid in the future.
But this system is not perfect. Sometimes scratching can break the skin, leading to infection. So scratch lightly and not too much.