Atherosclerosis is a condition in which artery walls accumulate fat deposits, cholesterol and other substances in and on it. The deposition is called plaque and over time, it hardens leading to narrowing of arteries. It gradually causes cardiovascular issues like such as coronary heart disease or peripheral artery disease, as well as a heart attack or stroke when plaque restricts the optimal flow of oxygen, blood and nutrients to body parts. Detected causes leading to atherosclerosis are high blood pressure, high cholesterol, and cigarette smoking. Now, scientists also doubt the active role of air pollution in causing atherosclerosis. Studies were conducted and results showed long term exposure to ozone has caused considerable increase in rate of carotid wall thickness progression and risk of new plaque formation in many cases. This in turn can injure carotid arteries — the two large vessels responsible for supplying blood to the head and neck. "This may indicate that the association between long-term exposure to ozone and cardiovascular mortality that has been observed in some studies is due to arterial injury and acceleration of atherosclerosis," says Meng Wang, Ph.D., assistant professor of epidemiology and environmental health. However, scientists still have a long way to go as they just know that long-term exposure to ozone causes atherosclerosis, but are unaware of its biological processes.