There are two main causes of high cholesterol: your genes and your diet.
The cholesterol made in your body is referred to as endogenous cholesterol. The liver is the main organ of the body that makes cholesterol. While high cholesterol levels are not healthy, your body needs still needs some cholesterol to perform many biological functions, such as making hormones (like estrogen or testosterone) and providing structure to cells. In fact, your liver makes most of the cholesterol your body needs on a daily basis.
Exogenous cholesterol refers to the cholesterol obtained from the foods you eat. It is usually obtained through a diet containing high amounts of cholesterol, saturated fats, or trans-fats. These fats are usually found in animal meats and processed foods, like chips or cookies.
A low-fat diet and exercise may help to lower your high cholesterol levels if it is only due to exogenous cholesterol. However, some cases of high cholesterol may have something to do with your family history. There are some inherited diseases of high cholesterol that may cause a defect in how cholesterol is absorbed in your body or made in the liver. In these cases, diet and exercise may not be enough to lower your cholesterol and medications can be used to lower it.
Sources:
Dipiro JT, Talbert RL. Pharmacotherapy: A Pathophysiological Approach, 6th ed 2005.

