Table 4.

Carcinogenicity classifications of chemical exposures found in cigarette smoke

Chemical	IARC	NTP
Tobacco smoking: Active and passive		K
Polycyclic aromatic hydrocarbons (PAHs)		RA
Polonium-210
Benzene	1	K
Vinyl chloride	1	K
1,3-butadiene	1	K
Nitrosamine ketone (NNK)

International Agency for Research on Cancer (IARC) classifications: 1 = Carcinogenic to humans, 2A = Probably carcinogenic to humans, 2B = Possibly carcinogenic to humans, 3 = Not classifiable as to its carcinogenicity to humans; U.S. National Toxicology Program (NTP) classifications: K = Known to be a human carcinogen, RA = Reasonably anticipated to be a human carcinogen. Source of exposure list contains most common exposure sources