Scratching That Bug Bite Feels Good at First — but Science Says Stop

You have probably been told since you were little: don't scratch that bug bite. But why does something that feels so good turn out to be a bad idea? Scientists now have a clearer answer, and they got part of it by putting tiny cone-shaped collars — just like the ones vets put on dogs and cats — on mice to see what scratching really does to the skin.

Researchers found that scratching can start a cycle that makes an itch worse, not better. When you scratch, your body sends more immune cells rushing to the area. Those extra immune cells cause more swelling and more itching, so you feel the urge to scratch again. It becomes a loop that is hard to break.

Dr. Daniel Kaplan is a skin doctor, called a dermatologist, at the University of Pittsburgh. His team studies how the body's immune system reacts in the skin. He was looking at a common type of itch called allergic contact dermatitis, which can be caused by things like poison ivy or the nickel found in some jewelry.

Kaplan's team put a rash-causing substance on the ears of mice. The normal mice scratched, and right away, immune cells flooded the area and the rash got worse. Mice that were bred with faulty itch-sensing nerve cells scratched less, and their rashes stayed much milder. This gave the team a clue that scratching itself was making things worse.

To be sure, the researchers fitted some normal mice with tiny cone collars so the mice could not scratch even though they still felt itchy. These mice also had much less swelling and fewer immune cells in the affected area. That proved it was the scratching — not just the itch — that caused the extra inflammation.

Kaplan said this matches what people experience every day. Leave a mosquito bite alone and the itch is gone in five or ten minutes for most people, he said. But start scratching and the bite becomes your friend for a week, getting itchier and more inflamed the more you scratch.

So what is happening inside the skin? The team looked closely at special immune cells called mast cells. Mast cells are like the first responders of the immune system — they rush to a problem and release chemicals to fight germs or poisons. One of those chemicals, called histamine, is what triggers the itchy feeling during an allergic reaction.

Scientists already knew that allergens, the things that cause allergies, can wake up mast cells. But Kaplan's team found that pain can wake them up too. When we scratch, we tend to scratch until it hurts a little. That pain causes nerve cells to release a chemical messenger called substance P, which activates mast cells through a separate pathway.

If scratching makes things worse, why does it feel so good in the first place? One old idea is that scratching helps animals brush off parasites like fleas or mites. Kaplan's team also found that mice that scratched had lower levels of a common skin bacteria called Staphylococcus aureus on their ears. That might explain why scratching feels rewarding — it has some small benefits in nature.

Even so, doctors say those small benefits are not worth it. Kaplan said people should avoid scratching, even though he knows it is easier said than done. For summer itches from bug bites or poison ivy, doctors suggest creams like hydrocortisone or calamine lotion, or a soothing oatmeal bath. Kaplan also shared a trick: menthol creams can fool the skin into feeling cold instead of itchy, helping you break the itch-scratch cycle — what he calls a cheat code.