Dina Rudick/Globe Staff
Molly Birnbaum (shopping at the Harvard Square farmers’ market earlier this month) lost her sense of smell after getting hit by a car six years ago but has worked to regain it. (Dina Rudick/Globe Staff)
Out for a run six years ago, Molly Birnbaum was struck by a car. Recovering from surgeries to repair a broken pelvis and torn tendons, she realized the blow had also left her completely unable to smell.
Then a recent college graduate and aspiring chef, Birnbaum said it was as if all the color drained out of life. Without the scent of roses, fresh bread, a spring rain, or even trash, she felt like she was living in a black and white world.
Estimates are that 1-2 percent of Americans under 65 have a limited sense of smell; that percentage rises to as high as 50 percent of those over 65. And doctors are just beginning to realize how important smell is to our well-being and our perceptions of the world.
“Your nose, sitting there in the middle of your face, is arguably the best chemical detector on the planet, but we usually fail to realize its importance until it goes missing due to illness or injury,’’ said Stuart Firestein, a scientist who studies the sense of smell, and the chairman of the biological sciences department at Columbia University.
Research into the olfactory process has increased dramatically in recent years, with the first smell-related Nobel Prize awarded in 2004, to an American team; the discovery that smell plays a role in some brain disorders; and the hope that a better understanding of smell may offer insights into how the brain works.
In the awarding of damages in court, the loss of smell has been estimated to account for 3-5 percent of someone’s earning potential, higher if the person has an occupation such as chef or perfume maker, according to standards set by the American Medical Association.
Losing vision, by contrast, is considered by the AMA to cost people 85 percent of their earnings, according to Rachel Herz, a smell researcher at Brown University.
But losing the sense of smell can be as profound a loss as going blind or deaf, said Herz, also author of a 2007 book called “The Scent of Desire’’ about the psychology of smell.
When Birnbaum lost her sense of smell, she lost her self-confidence, her enthusiasm for food, and her career as a chef. She no longer trusted herself to be alone at home, because she couldn’t smell if gas were leaking. She cataloged her losses, her newfound fascination with olfaction, and her efforts to regain that sense of smell in a book, “Season to Taste,’’ (Ecco/HarperCollins).
There is a wide range in the acuteness of people’s sense of smell, with some able to detect faint odors or distinguish between chemically similar smells, and others barely able to identify any smells. Some of it is anatomical: Some of us have a big, clear nasal cavity that allows the smells to bounce around a lot and be “smelled’’ more, while others have allergies that inflame the nasal passages and make it harder to smell.
A few people are born unable to smell. Most young people who lose their smell do so as a result of polyps or chronic inflammation which blocks the nasal passages, problems with sensory neurons, or head injury, as Birnbaum had, said Dr. Jim Schwob, chairman of the department of anatomy and cellular biology at Tufts University.
Training the nose, as Birnbaum did - by practicing detecting and defining different scents - may help restore smell if the physical damage isn’t too great, Schwob said.
Nerve cells involved in smell are among the few in the body that can be regenerated. Research in mice shows that even at an advanced age, they can regrow the 6 million to 8 million nerve cells needed to detect odors, and studies of people, who have about 5 million such cells, suggest we can do the same.
The loss of smelling ability may be one reason older people lose their desire for food - it just doesn’t taste as good when they can’t smell it. Loss of smell can also be an early sign of Alzheimer’s disease. But smell researchers are quick to note that far more people lose smell than develop Alzheimer’s, so older people shouldn’t necessarily be worried if they find their ability to smell deteriorating.
Smell memories seem to be encoded and remembered differently than sights and sounds, Herz said.
“You can visualize your car or hear the song you hear on the radio, you can’t really conjure the aromatic experience of a pizza,’’ she said. “Memories triggered by smell are unique - more emotionally laden. They feel different than if you hear or see something.’’
Birnbaum said she’s regained most of the memories she lost when she couldn’t smell. “When I smell the ocean now, it’s familiar and comforting,’’ she said. But she thinks she may have lost some very specific smell memories. The smell of salsa used to remind her of watching James Bond movies on the couch with her dad, she said. “I haven’t experienced that again.’’
Birnbaum gave up her dream of becoming a chef after the accident. But as she slowly regained and trained her sense of smell, she developed a new passion and profession: writing about food. Today, she’s a cookbook editor for America’s Test Kitchen, and remains an avid foodie.
“I am still today obsessed with cooking, and would spend all day in the kitchen if I could,’’ said Birnbaum, who lives in Cambridge and frequents area farmers’ markets.
Birnbaum said that she felt like she was more of a participant in life once her sense of smell returned.
“Without a sense of smell, I didn’t have to be immediately present in a way that I am when smells are coming at me,’’ she said.
Walking down the streets of New York City where she lived for four years after the accident, “I could be lost in my head and avoid people. But when my sense of smell came back, every person had a smell - the taxis had a smell, the candied nuts, hot dogs, pretzels . . .,’’ she said. “I didn’t realize how much I could not think about it if I didn’t have that cue.’’
Karen Weintraub can be reached at email@example.com.