There’s an old saying among people who work in public health: Tobacco is the only legal product that, when used as intended, will kill you. Decades of research have thoroughly documented the health problems that result from inhaling tobacco smoke – more than a dozen different types of cancer, heart disease, stroke, emphysema and other respiratory diseases, among others. Are these risks an inevitable part of smoking? Or is there a way of creating safe cigarettes without any of these hazards?
“I think it’s very unlikely,” says Stephen Hecht from the University of Minnesota Cancer Center, who studies tobacco carcinogens – substances that cause cancer. Tobacco smoke is a complex cocktail of at least 4,000 chemicals including at least 70 known carcinogens. No one has made a “cigarette that is significantly decreased in all of these [chemicals] and is still something people would want to smoke, even though the industry has worked on this for around 50 years,” says Hecht. “There’s no indication that it’s possible.”
As Hecht says, it’s not that the industry hasn’t tried. Journalist Will Storr recently documented a history of bungled attempts to create a safer cigarette, from one that passed the carcinogenic smoke through a filter made of another carcinogen – asbestos – to another that heated tobacco rather than burning it, but tasted of sulphur, charcoal, and burning plastic.
The problem is that no single step in the production or consumption process fills cigarette smoke with its dangerous constituents. Some constituents are in the tobacco leaves themselves at the point of harvesting. The plants can absorb metals and metalloids like arsenic and cadmium from fertilisers and the surrounding soil, while sticky hairs on their leaves can gather particles from the air, including radioactive elements like polonium-210.
When the harvested leaves are cured and dried, compounds within them are converted into tobacco-specific nitrosamines (TSNAs), a class of well-known and intensely studied carcinogens. And when the smoker lights up, chemical reactions in the burning leaves fill the smoke with carbon monoxide, hydrogen cyanide and a cocktail of carcinogens – the infamous polycyclic aromatic hydrocarbons (PAHs), and vapour-borne “volatiles” like formaldehyde and benzene. As long as you’re burning plant matter and inhaling the smoke, you’ll get a lungful of carcinogens. “There’s no getting around that fact,” says Neal Benowitz, a pharmacologist from the University of California, San Francisco.
As always with toxicology, it’s the dose that makes the poison, and a laundry list of ingredients is a poor way of assessing a product’s true risk. But it’s clear that many of the substances in cigarette smoke, particularly the well-studied TSNAs, PAHs and volatiles, are found at significant levels in both the smoke and the bodies of smokers who inhale it. And, they cause similar patterns of DNA damage to those seen in actual tumours.
The route of exposure also matters. Many of the chemicals in tobacco smoke are also found in other everyday sources, including foods. But there’s a big difference between taking these substances into your guts, where they pass through a soup of enzymes before being actively transported into the bloodstream, and sucking them directly into your lungs where they can passively diffuse into your blood.
There are some measures that could individually reduce the number of carcinogens in smoke: modifying the blend of tobacco; refining the curing process; including charcoal filters to absorb some of the volatiles; and so on. “But there’s no evidence that this does any good,” says Hecht. None of these measures completely deletes the full spectrum of carcinogens, and Hecht adds, “We tend to focus on the compounds that we know are dangerous, but that’s maybe only a few hundred of the 4,000 that are identified. There could be other things going on that we’re not aware of.”