Cholesterol is a soft, fat-like substance found in the bloodstream and in all your body's cells. Your body makes all the cholesterol it needs. Low-density lipoprotein (LDL or 'bad') cholesterol can join with fats and other substances to build up in the inner walls of your arteries. The arteries can become clogged and narrow, and blood flow is reduced. High-density lipoprotein (HDL or 'good') carries harmful cholesterol away from the arteries and helps protect you from heart attack and stroke.