Wound scab. Coloured scanning electron micrograph (SEM) of keratinocytes and a hair at the site of a skin wound. Keratinocytes are skin cells that contain the protein keratin. They migrate to the site of a wound and form accumulating layers that form the hard protective object called a scab. This covers the wound, allowing skin repair to proceed under the surface. Once the wound has healed, the scab will loosen and fall off. Magnification: x120 when printed 10cm wide.