New plaque tends to be soft, but is prone to rupturing. Plaque rupture can trigger the formation of a blood clot. Old plaque tends to have a lot of calcium and to be hard, which makes it somewhat less likely to rupture.
Atherosclerosis affects large and medium-sized arteries.
The type of artery involved and the location of the plaque varies with each person. Atherosclerosis is a slow, progressive disease that may start as early as childhood. People's susceptibility to atherosclerosis varies with their genetic make-up and their lifestyles. The circulatory system is very flexible and adaptive. Arteries are seldom totally blocked by atherosclerotic plaque.