LDL cholesterol, or low-density lipoprotein cholesterol, is often called the "bad" cholesterol because it carries cholesterol through your blood and can lead to plaque buildup in the walls of your arteries. This buildup, known as atherosclerosis, narrows the arteries and increases the risk of heart disease, stroke, and other cardiovascular problems

. LDL is a type of lipoprotein, which is a particle made of fats (lipids) and proteins that transport cholesterol in the bloodstream. Because cholesterol is fat-like and cannot dissolve in blood, LDL carries cholesterol to cells throughout the body. While cholesterol is necessary for cell repair and hormone production, too much LDL cholesterol can cause harmful deposits in arteries

. Health professionals measure LDL cholesterol levels in milligrams per deciliter (mg/dL) of blood. Generally, an LDL level below 100 mg/dL is considered optimal, 100-129 mg/dL near optimal, 130-159 mg/dL borderline high, 160-189 mg/dL high, and 190 mg/dL or above very high. High LDL levels increase the risk of cardiovascular disease, so maintaining a healthy LDL level is important for heart health

. In summary, LDL cholesterol is a lipoprotein that transports cholesterol in the blood, but excess LDL can cause artery-clogging plaque, raising the risk of heart attack and stroke, which is why it is termed the "bad" cholesterol