Women smell better than men.
Nonsmokers smell better than smokers.
And, most important in the view of researchers who tested how well people's noses work, middle-aged persons smell much better than do the elderly.
"This is the really important finding," said Richard L. Doty, a specialist in disorders of the sense of smell who directed the research at the University of Pennsylvania medical school.
"A great many of our elderly have lost much of their ability to smell. In fact, a great many can't smell at all."
Doty's research -- the first systematic testing of how the ability to detect odors correlates with age, sex and other variables -- involved 1,955 volunteers ranging in age from 5 to 99 and tests of 40 chemically simulated scents, including cinnamon, cherry, pizza, gasoline, tobacco, mint, soap, grass, lemon, motor oil and root beer.
Doty found that a person's olfactory ability is usually at its best between the ages of 20 and 40. The sense of smell begins to diminish slightly through a person's 50s and 60s and then drops rapidly through the 70s and 80s.
The study suggests that among people between the ages of 65 and 80, about 60 percent have severe losses in the sense of smell and about one-fourth have lost all ability to smell.
Among those over 80, the proportion with a severe loss was 80 percent. Nearly half could not smell anything.
At all ages, females scored higher than males. Middle-aged women scored about 5 percent higher; women over 65 scored 10 percent to 15 percent higher. In other words, as women grow older they lose less of their smelling ability than do men of the same ages.
Smokers at all ages scored lower than nonsmokers, confirming the general idea that the smoke damages the sensitivity of nerve endings in the nose.
"It's no surprise," Doty said in an interview, "that elderly people complain food doesn't taste good anymore. Many people don't realize it's because they can't smell anymore."
It is well established that the ability to smell is closely linked to the ability to taste. The aromas that waft up from a dish of food and into the nose are interpreted by the brain as part of the same sensations that come from the taste buds. This is why people with stuffy noses often think foods taste bland.
For the elderly, Doty said, the loss of the olfactory sense can have much more serious consequences. Because food is no longer enjoyable, many do not eat well and become malnourished. Because many cannot smell smoke or leaking gas, they are vulnerable to fires and asphyxiation.
"These are real problems that I don't think are being addressed," Doty said.
He said that there was no conclusive evidence of why smelling ability declines but that there was evidence that viral diseases can permanently damage olfactory nerve endings. As a person lives longer, Doty said, the damage may simply accumulate.
Each volounteer in the test was given cards containing 40 "scratch and sniff" patches. These contain microscopic capsules of chemical odorants; when scratched, the capsules break, releasing the aromas. The test, which Doty and his colleagues developed, is a standard one now used inabout 400 medical clinics to diagnose disorders of the sense of smell.
Each patch contains a different odor. In some cases only a single chemical is needed to produce a given smell. The chemical anathol, for example, is readily identified as licorice. To make an odor that people identify as chocolate, by contrast, takes a mixture of more than 20 chemicals.
In the test, each person scratches a patch, sniffs and then must identify the odor from a list of four widely dissimilar choices.
The average score achieved by middle-aged men was around 36 or 37 correct answers while that of middle-aged women averaged about two points higher. Women in their 70s averaged about 32 correct answers, but men of the same age could identify only 26 of 40 odors.
One finding that Doty said he could not yet interpret was that children, especially under 10, scored well below the middle-age average, getting scores comparable to those of people in their 60s and 70s.
Doty said it was not clear whether children simply had trouble coming up with the correct name for the odor. Even among children, however, the sex difference held very strongly.
He said that the female superiority also showed up when the test was used in Japan and within various racial groups in the United States.