They develop when white blood cells in arteries trigger inflammation by reacting to damage usually caused by a combination of high blood pressure and so-called bad cholesterol that irritates the walls of the artery. In an effort to repair the damage, white blood cells produce a foamy mixture that incorporates cholesterol and other stuff and then hardens. As plaque accumulates, arteries stiffen and narrow, sometimes preventing enough blood from flowing to the tissues and organs that need it and further driving up blood pressure.
