Hookah accounts for over half of the tobacco smoke consumed by young adult smokers in the US, a study has found. Toxicant exposures - such as tar, carbon monoxide and nicotine - were lower, yet substantial, for those young adults who smoked tobacco just using a hookah, compared to those who smoked both hookahs and cigarettes, researchers said. In the US, waterpipe tobacco smoking or hookah rates are increasing and cigarette smoking rates are decreasing, especially among young adults, according to the study published in the journal Tobacco Control. "Most hookah smokers in the US are not daily users, whereas many cigarette smokers smoke multiple times a day, so it may seem that the vast majority of public health and policy-related interventions should be directed at cigarette smoking," said Brian A Primack from the University of Pittsburgh School of Medicine in the US. "What our research shows is that hookah smoking contributes significantly to the burden of tobacco smoke-related toxicants inhaled by our young people. "Therefore, public health and policy efforts should explicitly address hookah smoking in addition to cigarette smoking," said Primack. The researchers analysed data from 3,254 adults aged 18 to 30 who were randomly selected in March 2013 to complete a questionnaire about their tobacco use. The participants were 63 percent female, 17.5 percent Hispanic and 10.1 percent black. The study combined self-reported frequency and quantity of tobacco consumption information with estimates from previous studies of the toxicants associated with cigarette and waterpipe tobacco smoking. In the 30 days before completing the survey, about 1 in 20 participants reported hookah smoking, and about 3 percent reported smoking both cigarettes and hookah. Cigarette smoking was reported by 23.4 percent of participants, with most of them smoking close to every day of the previous 30 days. Whereas smoking one cigarette involves about 10 to 12 puffs, each containing a volume of 50 millilitres of smoke, one 45- to 60-minute hookah session can involve 100 inhalations of about 500 millilitres each. This is why smoke loads can be so large for hookah users, even if they use infrequently, researchers said.