What are scabs?

What are scabs for, and is it OK to pick them?

Scabs put a lid on your cuts and scrapes, keeping blood in and nasty bacteria out. And, although it is fun, picking your scabs is dangerous, as it does the exact opposite.

So why is it dangerous to pick them?

Because scabs are like temporary plasters that cover your cuts until the skin has a chance to grow back underneath. They fall off on their own when the repairs are complete. Pick them off any sooner, and you risk opening up the wound again. At best, this will mean you just form another scab, so the wound takes longer to heal than it would have. But the second scab may be even bigger than the first, and is more likely to leave a permanent scar on your skin when it finally comes off.
At worst, the wound could become infected, and lead to much bigger problems.

Like what? What’s the big deal about a little cut?

Ordinarily, nothing. This is because your body has a strong immune system and a clever system of blood clotting to prevent too much blood loss from the cut. When you get cut, the cells nearby release signals that start two major chain reactions. One chain reaction brings immune cells to the area to fight off any bacteria trying to get in through the cut. These are white blood cells that drift around in your bloodstream waiting for an attack. Some of them, called macrophages, can punch holes in the bacteria or eat them whole and digest them with acids. Others, called B-Cells, make special proteins called antibodies, which surround the bacteria with white helper cells and summon killer cells to destroy them.

So why do we get scabs?

Scabs are made of the bits left over from this battle – the dead bacteria and immune cells – plus a special protein called fibrin. Fibrin is the end result of the other chain reaction – the one that leads to a blood clot. Again, when the wound occurs, special blood cells (this time called platelets) stick together and react with other proteins called clotting factors to build a clot. This clot is made from fibrin, a stringy protein that stretches across the wound, pulls the edges together and plugs the gap between them. This helps to stop any more blood from escaping, but also stops bacteria getting in.

What happens if they do?

It depends on what type of bacteria. Some of them we can fight off easily enough, and the wound heals over normally. Others, like the clostridium bacteria that cause gas gangrene, can dodge the immune system long enough to do serious damage. So you could end up losing an entire leg or arm from one infected cut! Worse still, if bacteria makes it into the bloodstream, it can travel around the body to other organs like your liver, heart or brain, doing damage there instead. And you really don’t want that to happen.

Yikes! I’m never picking a scab again!

If you’re healthy, and you keep the cut clean, none of this should be a problem. But the scab is there for a reason, and it’ll fall off on its own when it’s ready. Until then, just enjoy it. Admire the colours, impress your friends... but leave it alone!

From: http://www.sciencemuseum.org.uk/onlinestuff/snot/what_are_scabs_for_and_is_it_OK_to_pick_them.aspx