Cholesterol is a waxy, fat-like substance found in your blood that your body needs to build healthy cells, but high levels can increase risk of heart disease. There are two main types: LDL ('bad' cholesterol) can build up in artery walls, narrowing them and increasing heart attack and stroke risk; HDL ('good' cholesterol) helps remove other forms of cholesterol from your bloodstream. Diet, exercise, genetics, and weight all affect cholesterol levels. Blood tests measure cholesterol as part of routine health screening. High cholesterol typically has no symptoms, so testing is important. Treatment may involve lifestyle changes and medications if needed.