CHICAGO — Mimi Koberlein woke up one morning unable to smell the bacon her husband was frying for breakfast. Confused, she ran to the shower, grabbed her shampoo and inhaled deeply. Nothing. Two years later, Koberlein, 47, still can’t smell lemons, freshly cut grass, her three boys or any other fragrances of life. Diagnosed with anosmia, or smell loss, she has tried decongestants, nasal irrigation, oral steroids and acupuncture. But nothing has worked.

Without scented cues to guide her, Koberlein said she now feels anxious about personal hygiene, frequently changing her clothes on hot days. She often forgets to eat, throws away perfectly good food in case it has spoiled and puts up with remarks about how “great” it must be not to have to smell stinky feet or dog poop.

Smell is often considered the most expendable of the five senses, the one people often say they would sacrifice if forced to give one up. But the olfactory system is far from dispensable; it warns about gas leaks or smoke and makes food and drink palatable. Smells communicate information, connect us to the environment and play a vital role in emotions and mood, arousal, memory and quality of life.

There are no evidence-based preventive measures, interventions or treatment options for smell disorders and fewer scientists in taste and smell research than in other fields, according to the National Institutes of Health.

That leaves anosmics — and there are millions of them — on their own as they struggle with a life upended by a disability few understand.

Anosmics report higher levels of depression, anxiety and social isolation. Eating and drinking become difficult; they lose their appetite, have trouble cooking and gain or lose weight. They also frequently describe themselves as “frustrated,” “disconnected,” “missing out on something” and “lost,” according to published studies.

Sufferers seek validation — or at the very least some empathy — but the condition is often trivialized. They sometimes receive disinterested, rude or callous “help” from doctors and are subjected to “smell tests” by disbelieving friends and family or strangers, according to interviews and published surveys.

“I feel a little bit like a freak show,” said Koberlein of Redwood City, Calif., who has lost 30 pounds since her sense of smell vanished. “If a person loses any other sense, there are fundraising drives, public education or awareness campaigns — at least some sympathy for the situation. With anosmia, it’s just, ‘eh, that’s weird,’ and people move on. For those of us who suffer from it, a big piece of our life experiences are gone.”

At least 6.3 million Americans report problems with their sense of smell, a figure that is likely underestimated because many people aren’t aware of their problem until it’s severe or doctors fail to perform adequate tests, according to the National Institute on Deafness and Other Communication Disorders, or NIDCD.

Standardized olfactory tests have been available since the mid-1980s, but very few physicians use them, making it difficult to track the number of people affected.

The prevalence of smell loss increases dramatically with age, affecting more men than women. Smell disorders also can be caused by a physical blockage, viruses associated with the common cold, head trauma and exposure to toxins.

Evidence of smell and taste disorders in association with other health problems is also increasing, according to the NIDCD. People with early stage Alzheimer’s disease, nongenetic forms of Parkinson’s and polycystic kidney disease all report a reduced sense of smell. In addition, about 3 percent of those with olfactory disorders were born without the ability to smell.

Even though there have been no breakthroughs in treatments, some smell and taste clinics boast about outright cures or measurable improvements for their patients. But claims of cures are “unfortunate and misleading,” said olfactory researcher Richard Doty, director of the University of Pennsylvania’s Smell and Taste Center.

“Every hope is false hope,” said Andreas Keller, a research associate at The Rockefeller University, who has studied the hidden consequences of olfactory dysfunction. “There’s not much we can tell people.”

At the Monell Chemical Senses Center in Philadelphia, where scientists conduct basic research on taste and smell, staffers regularly receive desperate emails from people who have lost their sense of smell and want advice on treatment. “All we can say is, ‘I’m sorry, there’s nothing we can do,’ “ said Leslie Stein, Monell’s director of science communications.