Blood clot surrounding a hair shaft (brown), coloured scanning electron micrograph (SEM). Red blood cells (erythrocytes) are trapped within a fibrin protein mesh (yellow). Clots are formed in response to cardiovascular disease or injuries to blood vessels. As a clot ages, the normally concave-shaped red blood cells begin to deform into more crenated star-like forms known as echinocytes or burr cells (centre).