Smoking also causes increased mucous production and a narrowing of the small airways, as well as a decrease in ciliary function (cilia are microscopic, hair-like structures that help to 'sweep' the airways clean of harmful substances) (Ambrose, 2004; NCSCT, 2011). Finally, smoking is linked to decreased immunity, which leads to atherosclerosis and increased risk of infections such as pneumonia, tuberculosis and influenza (Ambrose, 2004; NCSCT, 2011).