Understanding Itching and Scratching: What You Should Know
Most of us have heard the persistent warning since we were kids: Don’t scratch that bug bite or rash; it’ll only make it worse. But, why does something that feels so relieving have such a negative reputation?
Itchiness can arise from various sources, including sometimes serious medical conditions. Yet, regardless of the reason, doctors have consistently advised against excessive scratching because it can harm the skin. Researchers have now begun to unravel why even a minor itch can spiral into an uncontrollable need to scratch.
How did they uncover these insights? One method involved using tiny “cones of shame” on mice to investigate what occurs at the cellular level when an itch is scratched—or left alone.
They also explored why a scratch brings a moment of relief. It’s not just humans or mammals that scratch; even fish do! This raises interesting evolutionary questions, and the mouse experiments hint at some potential protective role against germs—although that still doesn’t justify scratching.
Swelling and Increased Itchiness: The Consequences of Scratching
Dr. Daniel Kaplan from the University of Pittsburgh has been looking into a common type of itch known as allergic contact dermatitis, often triggered by irritants like poison ivy or nickel.
In a study, his team applied an irritant to the ears of mice. The regular mice scratched, leading to a rush of inflammatory immune cells to the area, which caused increased swelling. Interestingly, mice with defective itch-sensing nerves didn’t react the same way. But was scratching truly the key factor?
To find out, normal mice wore veterinary-style collars that prevented them from scratching. The result? They experienced considerably less swelling and fewer inflammatory cells.
Kaplan noted that this aligns with what people often observe: scratching can indeed make things worse. “If you ignore a mosquito bite, it usually goes away in about five to ten minutes,” he mentioned. “But if you start scratching, it can linger for a week, becoming itchier and more inflamed.”
The Immune System: Friends or Foes?
To delve deeper, Kaplan’s team examined mast cells, which are among the immune system’s first responders. When activated, they release substances that combat germs or toxins, or, via histamine, they can initiate itchy allergic reactions.
It’s been understood for a while that allergens can trigger mast cells, but pain can do so as well. Kaplan pointed out that when we scratch, we often scratch until it starts to hurt.
Pain-sensing nerve cells release substance P, a chemical messenger. In a study published last year, Kaplan’s team found that substance P can activate mast cells via a different pathway than allergens, which might explain why scratching tends to inflame already itchy rashes or bites further.
Why Does Scratching Feel Good?
We learn to avoid pain from things like touching a hot stove. But the relief of a good scratch seems to provide positive feedback in evolutionary terms. Why is that?
One theory suggests scratching might help remove parasites, such as fleas. However, Kaplan was also interested in findings from other labs that indicate mast cells could help fend off common skin bacteria like Staphylococcus aureus. Testing this, his team infected mice, then ran a variation of the cone-of-shame itching experiment. Those that scratched had lower levels of this bacteria on their ears, possibly due to additional inflammation or some mast cell-related substance.
Yet, these potential benefits don’t outweigh health advice. Kaplan emphasized, “Ultimately, scratching is harmful. You really should avoid it,” while acknowledging that this can be easier said than done.
Managing Minor Itches
How to handle an itch often depends on its cause, and there’s definitely room for better treatments. Currently, antihistamines and certain medications for hives can alleviate itching triggered by mast cells. There’s research ongoing into new strategies, like MRGPRX2 blockers, targeting the pathway identified by Kaplan’s team, which they hope will benefit conditions like chronic eczema.
For the common summer itches from bug bites or poison ivy, dermatologists recommend anti-itch products like hydrocortisone cream, calamine lotion, or oatmeal baths.
Another tip from Kaplan: Menthol creams can trick the skin into feeling cold instead of itchy, just long enough to potentially break the itch-scratch cycle. He likened it to a “cheat code.”
