What Your Nose Knows
Sense of Smell and Your Health
Your sense of smell enriches your experience of the world around you. Different scents can change your mood, transport you back to a distant memory, and may even help you bond with loved ones. Your ability to smell also plays a key role in your health. If your ability to smell declines, it can affect your diet and nutrition, physical well-being, and everyday safety.
Whether coffee brewing, pine trees in a forest, or smoke from a fire, the things we smell are actually tiny molecules released by substances all around us. When we breathe in these molecules, they stimulate specialized sensory cells high inside the nose. Each of these sensory cells has only one type of odor receptor—a structure on the cell that selectively latches onto a specific type of “smelly” molecule. There are more smells in the environment than there are odor receptors. But a given molecule can stimulate a combination of these receptors, creating a unique representation in the brain of a particular smell.
“It’s estimated that the number of odors that people can detect is somewhere between 10,000 and 100 billion, or even more,” says Dr. Gary Beauchamp, a taste and smell researcher at Monell Chemical Senses Center in Philadelphia. We all have different combinations of odor-detecting cells in our noses, he explains, so people vary greatly in their sensitivity to smells. “In fact, when you or I smell the same physical thing, our perceptions may be very different,” Beauchamp says.
Because smell information is sent to different parts of the brain, odors can influence many aspects of our lives, such as memory, mood, and emotion. For thousands of years, fragrant plants have been used in healing practices across many cultures, including ancient China, India, and Egypt. Aromatherapy, for example, aims to use essential oils from flowers, herbs, or trees to improve physical and emotional well-being.
To date, there’s little scientific evidence supporting aromatherapy’s effectiveness for most health issues. Yet memories of smell can be vivid and long lasting, which may have a positive effect.
“Lavender is a good example, which is touted as a relaxation odor,” Beauchamp says. “But the question is: Is that a relaxation odor because we’ve had past experience with this particular odor where we’ve been relaxed, and so we’ve learned the association?” Scientists continue to examine how different types of aromatherapies might affect our health and well-being.
Smell is also important for your perception of taste. Chewing your food releases aromas that travel from your mouth and throat to the nose. Without smell, we can detect only 5 basic tastes: sweet, salty, bitter, sour, and umami (savory). But our brains incorporate information from both taste and smell receptors to create the perception of many different flavors.
Some people may think they’ve lost their sense of taste if food begins to taste bland or slightly “off.” But in fact, they may have lost their ability to smell.
Many things can cause smell loss. A stuffy nose, or a harmless growth in the nose (called a polyp) can block air and thus odors from reaching the sensory cells. Certain medications, like some antibiotics or blood pressure pills, can alter smell. These effects are usually temporary. Your smell should come back once you’ve recovered or stopped the treatments.
But some things can cause a long-lasting loss of smell. A head injury or virus, for example, can sometimes damage the nerves related to smell. And your ability to smell may naturally fade as you get older.
“A good sized majority of people don’t know they have a problem with their sense of smell,” says Howard Hoffman, a public health expert at NIH. A national health and nutrition survey recently revealed that 12% of adults have a smell dysfunction. The problem increases with age, with 39% of those ages 80 and older showing a deficit.
“Quality of life issues from smell loss affect people differently depending upon their situation,” Hoffman says. “The effects can be enormous.” Food can become less enjoyable. You may lose interest in eating or change your eating habits, consuming a less healthy diet.
People who’ve lost their sense of smell sometimes try to boost flavor by adding more salt or sugar to their foods. But these additions might cause problems for those at risk for certain medical conditions, such as high blood pressure, kidney disease, or diabetes. Talk with your doctor if you think a smell deficit might be affecting your quality of life.
Smell loss can also put you in harm’s way if you don’t notice a “warning” smell. The recent national health and nutrition survey found that 1 in 10 people couldn’t identify the smell of smoke, and about 15% couldn’t identify the smell of natural gas. “As people get older, those rates go up,” Hoffman says. For those ages 70 and older, 20% couldn’t identify the smell of smoke, and 31% couldn’t recognize gas odor.
“With age, there is a decline in the ability to smell to some extent in the nose, but much more in the brain itself,” says Dr. Davangere Devanand at Columbia University, an expert on neurodegenerative diseases and smell loss. “The main reason appears to be that the functioning of the brain regions involved in smell and memory become impaired as we grow older.”
But problems with your ability to smell may be more than normal aging. They can sometimes be an early sign of serious health conditions, such as Parkinson’s disease, Alzheimer’s disease, or multiple sclerosis. Devanand’s group is currently studying the relationships between smell dysfunction and Alzheimer’s disease.
If your food doesn’t smell or taste the way you think it should, talk to your doctor. Health care providers can give you a “scratch and sniff” smell identification test to help assess the kind of smell disorder you might have. This test alone can’t diagnose more serious health problems, but it can be informative when used alongside other tests.
Smell may be the most mysterious of our 5 senses, Beauchamp says. “We know quite a bit about smell loss and can diagnose this fairly well. But, for the most part, we have no treatments that are reliable and widely accepted” for long-lasting cases of smell loss. Some studies suggest that smell training may help you improve your ability to discriminate and identify odors. It may stimulate growth of new receptors or improve your brain’s ability to interpret low levels of odors, Beauchamp explains. But researchers are still learning how and whether this works.
Like all of your senses, your sense of smell plays an important part in your life. If you think you’re experiencing a loss of taste or smell, see your health care provider. There may be ways to help fix the problem. If not, your doctor can help you learn to cope with the changes in smell and taste.
Olfactory deficits predict cognitive decline and Alzheimer dementia in an urban community.
Devanand DP, Lee S, Manly J, et al. Neurology. 2015 Jan 13;84(2):182-9. doi: 10.1212/WNL.0000000000001132. Epub 2014 Dec 3.
New chemosensory component in the U.S. National Health and Nutrition Examination Survey (NHANES): first-year results for measured olfactory dysfunction. Hoffman HJ, Rawal S, Li CM, Duffy VB. Rev Endocr Metab Disord. 2016 Jun 10. [Epub ahead of print] Review. PMID: 27287364.
NIH News in Health, Aug 2016