Your skin has three layers.

Small cuts that only affect the top layer usually heal without scars. But for deeper cuts, your body has a stronger response, and that’s when a scar forms.

When you get a cut, blood rushes in to fight germs and stop the bleeding. The blood then dries into a scab. Under the scab, special cells called fibroblasts build strong collagen fibers to close the wound.

A scar is made of this thick collagen. It’s tougher than normal skin and doesn’t grow hair or have sweat glands. The collagen stays for life as your body’s way of making sure the hurt area is strong enough to fight future cuts and keep infections out.