A matter of taste and smell.

What if you couldn't taste your favorate foods or smell poisonous fumes? One teen tells how smell and taste losses changed his life.

Riding his mountain bike, watching TV, or hitting the books, Matthew Clarke, 19, seems like your average teen--with one exception: He has poor taste, and we don't mean the plaid-shirt-with-a-polka-dot-corduroys kind.

It began with a severe auto accident just over a year ago, when the car Matthew was riding in skidded into a telephone pole. Flung from the back seat, Matthew smashed into the windshield head-on. After 12 hours of surgery to repair several fractured facial bones--followed by weeks of recovery--Matthew began to notice something odd. "My food tasted bland," he says. Sure, he could still eat cheeseburgers and pizza, but they weren't the same. "I can't really taste cheese anymore," he says.

Had Matthew's sense of taste been injured in the accident? Not quite, says Dan Kurtz, director of the Smell and Taste Disorders Clinic at the State University of New York at Syracuse. Matthew's problem was a partial loss of his sense of smell. "If Matthew can't tell its flavor."

You've probably noticed that taste and smell are linked. Ever eat when your nose is stuffed? If you still don't believe it, try this: Close your eyes, plug your nose, and chew on a variety of flavored jelly beans one by one. Without your sense of smell, says Kurtz, the only thing you can say is that the candies all taste "sweet." That's because taste buds made of sensory cells on your tongue detect only four primary tastes--sweet, salty, bitter, and sour (and possibly a fifth "meaty" taste).

To detect any other flavors, you need the direct involvement of your "sniffer." To see what we mean, unplug your nose while eating the jelly beans. You can suddenly identify their cherry, orange, and lemon flavors. That's because each candy's aroma wafts up into your nasal cavities, stimulating smell sensors that send signals to your brain. In millisecons, your brain interprets the signals as a particular flavor (see diagram, p. 24).

THE NOSE KNOWS

Of course, Matthew's problem is not merely a stuffy nose. Kurtz theorizes that when Matthew's head hit the windshield, he damaged or severed some of his olfactory neurons, millions of tassel-like nerve cells in the nasal cavity that--when funtioning--can detect some 10,000 odors (and nearly as many flavors). Scar tissue may have formed, perventing some of Matthew's olfactory neurons from sending signals to his brain.

Compared with losing other senses sucha as sight or hearing, Matthew's smell and taste deficits may seem trivial. But scientists who study these senses theorize that smell and taste may have evolved as built-in "alarm systems" to protect our bodies from danger--poisonous gases or spoiled foods, say. Without these senses, we expose ourselves to hazards. For instance, if Matthew can't smell smoke or natural gas, he has little warning of a nearby fire or possible explosion. Also, due to his loss of smell, Matthew has trouble sniffing spoiled foods, such as nose-wrinkling rotten milk, which can be filled with harful bacteria that can make you ill.

Mathew's case of hyposmia, a partial loss of small, is not uncommon. At any given time, says Kurtz, about one in four Americans has hyposmia (and therefore a related taste deficit). Causes other than head trauma include viral infections, nasal allergies, certain medications, aging, and smoking. In addition, an estimated two to four million Americans suffer from anosmia, a complete loss of smell. Some of these people were born with a genetic condition that interferes with the development of their olfactory system. They have never been able to smell--good things or bad.

THE BRIGHTER SIDE

The sweet-smelling news for Matthew is that his chances of recovery are relatively good. About 30 to 40 percent of people with smell losses caused by head trauma do recover, at least partially, says Kurtz. Unlkike some other neurons in the body, olfactory neurons can repair themselves over time and once again send signals to the brain. With that could come a renewed sense of taste.

In the meantime, Matthew is learning to live with his losses. As a safety measure, his family has installed extra fire alarms in their home. Matthew carefully checks the expiration dates on milk, cheese, and other foods products. Thinking back to the accident, he's thankful that he can still walk, see, and think. Truth is," "I hadn't thought about smell and taste before," Matthew says. "It's something we take for granted."