We all know that picking and scratching at a scab is a bad idea – it only increases healing time and can even lead to infection. But a healing scab just begs to be scratched. Why do scabs itch so much?
“I say that skin is very smart and insanely stupid at the same time,” said Dr. Adam Friedman, professor and chair of dermatology at GW Medical Faculty Associates, a nonprofit organization affiliated with George Washington University, told Live Science. “That doesn’t seem to make any sense. Why would that happen when it could actually lead to bad things?”
Friedman pointed out that scabs aren’t the only skin condition that prompts you to scratch when you shouldn’t. Inflammatory skin diseases – such as eczema, psoriasis and acne — all itch for different reasons. But when a scab does develop, the wound healing process is to blame.
This process has three phases. After you suffer a skin injury like a scrape or cut, the inflammatory phase begins with clotting — which reduces blood loss — and immune cells rush in to remove debris and bacteria from the wound. Once the purification is complete, specialized cells send a signal to the immune system to reduce inflammation.
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This leads to the next stage: the proliferation phase. At this point, new skin cells and blood vessels form to repair the damage caused by the wound. This phase overlaps with the last step, the remodeling phase, in which the new cells reorganize to bring the skin as close as possible to its original shape.
In an average cut, the inflammatory phase lasts 10 to 14 days, and that’s when most of the itching takes place.
“Wound healing is itchy, period,” Friedman said. “You can’t do anything about it. It’s going to itch because the inflammatory cells that are coming in are secreting things for good reasons. But the same signals they put out will actually sensitize the sensory nerves in the skin.” These particularly sensitive skin nerves can itch until the inflammatory phase subsides.
In addition, the scab itself can cause itching. “Every time that scab moves or shifts… that movement will also tell those sensory nerves to send a signal to the brain to itch.” Not to mention they are a good food source bacteriaso that more inflammation can be stimulated.
“And what do people do then? They’re picking on it,” Friedman said. “And that creates more inflammation, more trauma. And that sustains the early stages of wound healing.”
So how do you dull the itch? Friedman suggested trying not to leave the scab at all.
“Scab is bad,” Friedman said. “It’s like a boulder in the middle of the road… It’s a barrier to allowing these new cells to invade in a very linear fashion.” This slows down the wound healing process.
Instead, Friedman said, the best way to care for a wound is to keep it moist — for example, by applying petroleum jelly (like Vaseline) or silicone gel – and covered with a bandage. This even applies to wounds that are already crusted. A wet scab isn’t pretty, but it heals faster and is less itchy than a dry scab.
“It’s going to look very thick, almost like slime, and people are going to be like, ‘Oh, it’s so gross,'” Friedman said. “No, that’s actually how you want the wound to be. This gel-like material allows your cells to go straight through” and remodel themselves properly.
Originally published on Live Science.
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