Cigarette smoking is believed by most research workers in this field to be an important factor in the development of cancer of the lungs and the throat and is believed to be related to cancer of the bladder(膀胱) and the oral cavity(口腔). Male cigarette smokers have a higher death rate from disease than non-smoking males. Female smokers are thought to be less affected because they do not breathe in the smoke so deeply. The majority of physicians and researchers consider these relationships proved to their satisfaction and say. 'Give up smoking. If you don't smoke, don't start. 'Some physicians and research workers though their small number is dwindling(减少)even further are less sure of the effect of cigarette smoking on health. They consider the increase in repiratory (呼吸的)diseases and various forms of cancer may possibly be explained by other factors in the complex human environment-atmospheric (大气的) pollution, increased nervous stress, chemical substances(物质) in food, or chemical pesticides(杀虫剂)that are now being used by farmers in vast quantities to destroy insects and small animals. Smokers who develop cancer or lung diseases, they say, may also, by coincidence (巧合)live in industrial areas, or eat more canned food. Gradually, however, research is isolating (隔离) all other possible factors and proving them to be statistically (统计) irrelevant (不相关). While all tobacco smoking affects life expectancy and health, cigarette smoking appears to have a much greater effect than cigar or pipe smoking. However, nicotine consumption (用量) is not made less by the latter forms, and current research pointed out relationship between all forms of smoking and cancer of the mouth and throat. Filters(过滤 ) and low tar(焦油) tobacco are claimed(声明) to make smoking to some degree safer, but they can only marginally(边缘地) reduce the danger. Male smokers are more affected by smoking than female ones because ______.