Smokers suffer from impaired smell.

Smokers suffer from impaired smell

A rose may not smell as sweet to longtime cigarette smokers. New research suggests repeated exposure to chemicals in cigarette smoke damages the sense of smell, creating a deficit that can persist for years after a smoker kicks the habit.

While some research teams previously reported that smoking harms a person's sense of smell, others found no link between smoking and olfactory function, or the ability to detect odors. The new report adds credence to the growing belief that cigarette smoking causes long-term but reversible deficits in olfactory ability.

A group led by Richard L. Doty, of the Smell and Taste Center at the Hospital of the University of Pennsylvania in Philadelphia, studied 553 men and 85 women working at a chemical manufacturing facility. The researchers interviewed the workers about current and past smoking histories and culled information from the company's personnel office to control for workplace exposure to chemicals that could interfere with the sense of smell. Study participants took a standardized, multiple-choice "smell test" in which they were asked to identify whiffs of 40 different odors, such as pizza, motor oil and banana.

Compared with people who had never smoked, current cigarette smokers were nearly twise as likely to show impaired ability to smell, the researchers found. Ex-smokers showed a reduced ability to detect odors that improved with the number of years elapsed since quitting. In the March 2 JOURNAL OF THE AMERICAN MEDICAL ASSOCIATION, Doty and his colleagues say their work shows that a person with a two-pack-a-day cigarette habit spanning 10 years would have to abstain from cigarettes for 10 years before regaining a normal sense of smell. The researchers detected no olfactory deficits among pipe or cigar smokers, but they suggest this finding reflects the small number of pipe and cigar smokers in the study.

Although scientists have yet to pin down any biological basis for cigarette smokers' impaired performance on the smell test, Doty says he suspects that certain chemicals in tobacco smoke, such as acrolein, acetaldehyde, ammonia and formaldehyde, damage the olfactory receptor cells in the nose. Animal studies have shown that exposure to cigarette smoke once or twice a day for a week can cause anatomic changes in such cells, he says. Researchers don't know whether such changes persist over time.

Scientists do know that in animals, damaged olfactory receptor cells die and are replaced by healthy ones. Doty's group speculates that a similar replacement process begins in the human nose when people stop smoking. "There is some repair possible, but it's not a very rapid repair," says cell biologist Robert C. Gesteland of the University of Cincinnati College of Medicine.

While an acute sense of smell enhances the taste of food and the appreciation of a rose, olfaction is far more than a frivolous sensory ability, odor experts maintain. The nose alerts people to many dangers, including fire, spoiled food and toxic chemicals. "If you can't smell leaking gas, you're in peril," Doty says. Scientists don't really know how olfactory defects affect human health, but Gesteland notes that odor cues influence a variety of human activities, including sexual behavior and mood.