Cigarettes are a product consumed through smoking and manufactured out of cured and finely cut tobacco leaves and reconstituted tobacco, often combined with other additives, then rolled or stuffed into a paper-wrapped cylinder (generally less than 120 mm in length and 10 mm in diameter). The cigarette is ignited at one end and allowed to smoulder for the purpose of inhalation of its smoke from the other (usually filtered) end, which is inserted in the mouth. They are sometimes smoked with a cigarette holder. Nicotine, the primary psychoactive chemical in tobacco, is addictive. Cigarette use has also been shown to cause multiple types of cancer, heart disease, respiratory disease, circulatory disease, birth defects (which include mental and physical disability) and emphysema. On average, each cigarette smoked shortens lifespan by 11 minutes.