Do cigarette filters provide any benefits to the smoker, or were they simply created by the tobacco companies to make customers think they were addressing the health risks of smoking? Filters seem to trap something, as evidenced by the discoloration noticed on any discarded butt. While I'm on the topic, why don't manufacturers make filters out of something that actually decomposes when exposed to the environment, rather than something that litters our beaches, parks and sidewalks forever?
Why don't they design a biodegradable butt? Yeah, that's a real puzzler—if there's one thing cigarette makers are known for, it's their deeply felt sense of social responsibility. Probably just nobody's brought it to their attention yet. We'll come back around to this in a minute, but let's talk in the meantime about the first part of your question.
The short answer is no, filters don't really do anything. They're about the illusion of a lighter cigarette rather than the fact of one. This revelation shouldn't exactly be shocking, but you may be interested to learn that manufacturers didn't set out to make a deceptively useless filter—early on, cigarette manufacturers appear to have actually wanted something that would remove some of the harmful materials their products contained.
You old enough to remember the 1950s, Tom? Americans had by then been puffing happily away on their mass-manufactured smokes for half a century, while at the same, time lung cancer—previously quite rare—was becoming epidemic. It was only after World War II that scientists started putting the pieces together. As we know now, cigarette-industry players—Philip Morris, Lorrilard, et al.—were soon well aware of the link between their products and lung cancer; they just didn't feel like sharing this info publicly. Manufacturers did, however, put some cash behind a project to mitigate, in earnest, some of the malign side-effects of smoking: the cigarette filter. And they appealed to textile and chemical companies for help.
An early result was the Kent Micronite filter, designed by Lorillard; it used asbestos fibers to trap, uh, harmful substances. The fact that it was literally full of carcinogenic matter wasn't what made it unpopular. Rather, the thing worked too well: The Micronite, which removed 30 percent of tar particulate, also removed the cigarette's flavor and forced smokers to pull harder on their draw. It also proved excessively tricky for mass production, as did filters using natural materials like cotton and wool, which have a nonuniform structure. What manufacturers needed was something that could be made in volume and at low cost—Americans at the time were, after all, going through about 400 billion cigarettes a year.
The answer turned out to be a filter made of cellulose acetate. This did, indeed, block a little tar and toxic gas, but smokers, ever resourceful, responded by changing their behavior—smoking more, taking deeper puffs, etc.—thereby making the practical effect of the cellulose-acetate filter approximately nil. At this point cigarette makers basically threw up their hands, yielding to the intractability of what was known as the "filter problem." As a 2011 paper in the journal Tobacco Control put it, researchers had "confronted an engineering contradiction: to design a cigarette filter that would appreciably reduce the health hazards imposed by smoking (caused by tar, nicotine and gases) while preserving the taste and 'satisfaction' that smokers craved (provided by tar, nicotine and gases)."
Accordingly, the industry did something that conformed much more to our expectations for its behavior. One chemist discovered that if you adjust the pH in cellulose-acetate filters, you can get them to change color during the smoking process, making it look like some really bad stuff is being screened out. Thus does the filter story take its ghoulishly cynical left turn: Hoping to keep concerned smokers onboard but unable to actually make cigarettes safer, manufacturers settled for tricking the smokers into thinking the cigarettes were safer.
Where does that leave us? The fact that filters change smokers' MO has produced one observable public-health effect: a shift in the type of cancer you get from smoking. A 2011 study in the International Journal of Cancer, based on 30 years of research, suggested that while declining rates of squamous cell cancer can be attributed to cigarette filters, so can increasing rates of another type of cancer, adenocarcinoma, which occurs in parts of the lung that smoke reaches through deeper inhalation. You can't win for losing.
Anyway, getting to your other question: Cellulose-acetate filters are photodegradable, meaning UV in sunlight breaks them down somewhat. This might be OK but for the fact that so many of them—globally about 4.5 trillion butts become litter every year, out of 6 trillion cigarettes annually smoked—end up in the environment. We don't yet know what damage this is doing, though (for instance) under lab conditions, one cigarette butt in 1 liter of water is enough to kill both salt- and freshwater fish. The tobacco industry's position? It's smokers' responsibility not to litter—full stop. You can expect to be waiting on your better filter just a while longer.
Send questions to Cecil via StraightDope.com or write him c/o Chicago Reader, 350 N. Orleans, Chicago 60654.