The pain came without warning. It was February of last year, and the man was eating dinner. He’d just reached for a glass of wine.
“It really burned my mouth when I started to drink,” says Greg (the healthcare worker in Toronto asked for his name to be changed). The odd and disquieting sensation had no apparent cause—no burns or cuts or other injuries. Yet the burning and tingling Greg felt on his tongue and the roof of his mouth persisted. “It was very intense during the middle of the day and then subsided at nighttime,” he says.
Perhaps, he was told when finally visiting the family doctor months later, the pain was related to a yeast infection on the tongue. But the prescribed anti-fungal medication made no difference. Next Greg saw a dentist, who found no abnormalities in his mouth and recommended he get a blood test to rule out an autoimmune disorder. Eventually, though, one of Greg’s doctors referred him to Miriam Grushka, an oral medicine specialist in Toronto. Grushka has spent decades studying and treating Greg's condition, which is called burning mouth syndrome.
“People say they feel like they burnt their tongue on a cup of coffee, but the burning never went away,” says Grushka. “In the vast majority of cases it’s benign, but it’s very uncomfortable.”
Each week, she sees around 15 patients who have burning mouth syndrome or similar conditions. These hallucinations, or phantoms, are characterized by a taste or feeling in the mouth that will not go away. Oral phantoms are often treatable, and are rooted not in the mouth but the brain. But much else about these phantom feelings is still a mystery. Grushka and other researchers are still unraveling why they happen and how to banish them.
Most people don’t consider taste to be quite as useful as senses like vision or hearing. Throughout human evolution, though, taste has been important for survival. It guided us to nutrient-packed foods and warned us of poisons and spoiled food. When the facial nerves that carry this vital information are damaged, however, we wind up with spurious tastes or pain.
“The worst thing that can happen to a person in the taste system is to get a phantom; it’s very disruptive and very, very hard to live with,” says Linda Bartoshuk, an experimental psychologist at the University of Florida in Gainesville. “You can imagine how frightening it would be to wake up with something like a strong bitter taste in your mouth and not be able to get rid of it.”
It’s not uncommon for people to develop a metallic taste in the mouth during pregnancy, though this is related to hormone changes. The phantoms that Bartoshuk studies often have a metallic tinge as well, but they can be any basic taste, from sweet to bitter. Other times, oral phantoms can be a feeling in the mouth. Aside from burning pain, this can mean roughness, dryness, numbness, a gummy coating on the tongue or teeth, or a sensation that something is caught in the throat.
Burning mouth pain is usually concentrated in a particular area of the lips, gums, tongue, or roof of the mouth. Taste phantoms are not tied to any one area. “The phantom is kind of disembodied,” Bartoshuk says. “People tend to just feel it coming from all over.”
Oral phantoms typically begin very suddenly and can be impossible to ignore. This is especially true for burning mouth syndrome. “It could be in the range of toothache pain, so the burning can be very intense and it can be associated with a lot of with emotional fallout because people are just absolutely miserable with it,” Grushka says.
There’s no evidence that oral phantoms are symptoms of an underlying disease, Bartoshuk says. “They’re actually a reflection of the way the taste system is wired in the brain.”
She believes that these sensations often share a common cause. It all starts with damage to one of the nerves that carry taste information from the mouth to the brain. There are three of these nerves on each side of the mouth, gathering taste from different parts of the tongue.
The brain areas that process taste input from each of these nerves communicate with each other. Normally, each sends messages that dampen the others’ sensitivity to taste information and pain. But if one nerve is damaged, the others will become more responsive.
“By having multiple nerves carry taste and by having them inhibit each other in the brain, you can protect the system against one or two of them getting damaged,” Bartoshuk says. “That allows the person to have a normal sense of taste even though they may have a lot of damage to taste nerves.”
Sometimes, however, the brain may become overly sensitive and read the normal, background activity of the nerves as taste information. “The release of inhibition in the brain is so energetic that I think what happens is you may actually be tasting ‘noise’ in your nervous system,” Bartoshuk says. “Suddenly it ups the threshold of perception and you taste it.” This is similar to how ringing in the ears is thought to come about, when the brain’s auditory system becomes more active to try to compensate for hearing loss.
Bartoshuk suspects that the more profoundly the taste nerves are injured, the more likely someone is to get a phantom. A common cause of this damage is repeated ear infections, because the chorda tympani—the taste nerve that innervates the front of the tongue—runs through the middle ear. Head trauma and radiation or chemotherapy can also impair taste nerves enough to spark a phantom. Why some people experience burning pain or roughness, others a salty taste, and others still sweetness or bitterness is not clear.
It’s also not known how common oral phantoms are. Estimates for burning mouth syndrome vary; one study found a prevalence of around 3.7 percent in adults. Postmenopausal women seem to be especially susceptible. This could be because the ability to taste bitterness declines at menopause. On top of this, women are more likely to be supertasters. “Women have a double whammy,” Bartoshuk says. “Both of these things put you at a highly vulnerable position for burning mouth syndrome, and maybe a little bit of extra damage and you’re over the line and you get it.”
To diagnose a person with taste phantom or burning mouth syndrome, Bartoshuk and her colleagues numb their mouth. Usually, the phantom actually gets worse. “That’s a tipoff that they’re in the brain,” Bartoshuk says. She thinks that, until it wears off, the anesthetic removes even more of the sensory input that would normally quell the phantom.
On the other hand, people with phantoms often find that their symptoms improve while they are eating. “If you add taste—like sucking on a candy—then the burning disappears completely,” Grushka says.
Taming a phantom
Even today, many physicians are not familiar with oral phantoms.
“Not only is it unpleasant in itself, especially if it’s bitter, but it’s frightening,” Bartoshuk says. “You go to your doc and you tell him you have a symptom like this and they've either never heard of it or they can’t imagine what it is, and the fear is that it’s something awful that they’re not able to diagnose.”
Sometimes, people request unnecessary treatments like having their fillings changed or implants taken out in hopes that it will help their symptoms, Grushka says. “I do a lot of continuing education trying to tell dentists, if a patient comes in with any of these bizarre symptoms, don’t do anything irreversible because that will just probably make it worse.”
In fact, invasive procedures are not needed to treat burning mouth syndrome or taste phantoms. Grushka discovered the treatment for these conditions by chance. Some years ago, one of her patients was prescribed a drug called clonazepam for an unrelated condition—and her burning mouth pain went away. After the woman told Grushka what had happened, she began testing the drug at different doses. It turned out that a very low dose of clonazepam eased both burning mouth pain and taste phantoms.
Clonazepam (often sold under the brand name Klonopin) belongs to a class of drugs that are often used to treat epilepsy and panic attacks. These drugs can also ease oral phantoms by tamping down the brain’s hypersensitivity to messages from the uninjured taste nerves. “We trick the brain by giving it a drug that does what the taste input [from the damaged nerve] used to do,” Bartoshuk says.
Grushka estimates that the drug is effective for about two thirds of the people she prescribes it to. It’s not clear why some people respond to medications when others don’t, or why the drugs are more effective in certain people. Even if medication does not help, however, oral phantoms will usually fade with time. They may vanish in a few days, linger for several years, or fade and then flare up again later. In some cases a phantom will persist indefinitely, but this is rare.
“Fortunately, the nervous system tends to regenerate when there’s damage to taste and so these things tend to heal themselves,” Bartoshuk says.
Our senses of taste and smell are closely tied together. In fact, both the aroma and much of the flavor of any given food stems from compounds called volatiles that travel into the nose while we’re eating. And people can hallucinate smells just as they do taste. But taste and olfactory phantoms seem to work a little differently.
For one thing, a taste phantom is always a simple quality like sweetness or saltiness, but people often have trouble describing their olfactory phantoms. “You can create a quality in the brain that you’ve never experienced through the nose,” Bartoshuk says. “Taste is a simpler sense.”
People sometimes liken their olfactory phantom to some kind of chemical that they’d expect to smell in an industrial setting, says Donald Leopold, an ENT physician at the University of Vermont Medical Center in Burlington. When people can put a name to what they’re smelling, they often describe the odor as being like burned rubber, cigarette smoke or ashes, feces, or spoiled meat. The smells can sometimes be so powerful that they cover up the flavors of actual food. “People will say that they’ll have a burned rubber sandwich for lunch rather than a ham sandwich,” Leopold says.
Like oral phantoms, olfactory hallucinations may be related to sensory processing that has gone awry, but their exact cause is not known. They’ve been linked to a number of conditions including upper respiratory infections, head trauma, radiation therapy, sinus disease, migraines, depression, and, very rarely, brain tumors. But they sometimes strike in people with no history of any of these ailments.
“There’s no known treatment that’s predictably effective, largely because we don’t know what causes this,” Leopold says. A few years ago, he tested whether cocaine could provide relief from olfactory phantoms based on claims that had been made during the 1960s. “We tried that multiple times on some people, and it didn’t have any long-term effect,” he says. He’s now investigating the causes of olfactory phantoms, and has started to take MRI scans of the heads of people who are experiencing them. These images, he hopes, will eventually provide a clue to which parts of the brain are involved.
Olfactory phantoms are most common in women aged 30 to 50, and often begin for no apparent reason. “They’ll be sitting in their office or reading in a bus or something and they’ll look around to other people to see if they can smell this smell and they’ll ask their friends and they’ll be reassured that there are no bad smells around, but they’re sure there are,” Leopold says. “I’ve had people refit their entire house, rip up carpet, get new sofas and so on just because they thought they smelled.”
In most cases, the phantom vanishes after a few minutes or after the person has gone to sleep. Rarely, the phantom does not abate; Leopold occasionally sees patients who have had olfactory phantoms for decades. Some people have asked him to surgically eliminate their sense of smell because their phantoms are so unpleasant. Even then, the phantom sometimes will return. But in the vast majority of cases, olfactory phantoms will disappear on their own within a year.
Why olfactory phantoms so often take the form of noxious smells isn’t understood, Leopold says. By contrast, disagreeable taste phantoms are common, but not overwhelmingly so. One woman Bartoshuk examined liked to eat butterscotch candy because it paired so well with her salty phantom. Bartoshuk herself has given herself short-lived phantoms in the lab by anesthetizing her chorda tympani nerve. “I get a gorgeous sweet phantom,” she says. “Although they’re frightening, they don’t have to be unpleasant.”
One of Leopold’s patients did perceive the scent of peaches, while another smelled butterscotch candy. “But even those people said that 24/7 peaches is still not pleasant,” he points out.
Life with a phantom
While waiting for their phantoms to lift, there are a few tricks that people use to make them more bearable. They may chew gum or sip cola to mask their taste phantoms. Wearing bleaching trays seems to dampen burning mouth pain in some people, though it’s not certain why. Those with olfactory phantoms can sometimes find a few hours’ relief by dripping saline into their noses to clog the upper part of the nasal cavity.
Still, living with a taste or smell that never goes away can be exhausting. “When it’s pretty bad it’s all they can think about,” Grushka says. “They don’t want to socialize, they don’t want to go out.”
People who live with phantom smells or tastes are often hesitant to talk about them. “Many of them haven’t mentioned this to their primary care providers or their friends or family because they don’t want to have people think badly of them,” Leopold says. As a result, he says, these phenomena are hugely underreported. “So we’re just beginning to understand the importance of this and how much it affects people.”
Though oral phantoms are easier to treat than olfactory ones, there is still a lot we don’t know about them—such as why medications help some people and not others. “I think there are multiple causes and only some of them are going to be cured by the cure we know; we have to find out how the others work,” Bartoshuk says. She’s also investigating whether volatiles might be a new option for treating oral phantoms.
These chemicals tune our perception of taste all the time. When “you eat a nice sweet strawberry, part of the sweetness is coming from sugar, part of it is coming from volatiles that enhance the sweet message in the brain,” Bartoshuk says. “The question is, could we put taste input into the brain through volatiles and help people who’ve had taste damage get rid of phantoms?”
She and her colleagues want to treat phantoms more quickly and in more people. They’ve seen how intrusive these tastes, pains, and smells can be, and how people’s concern does not necessarily end when they are diagnosed. Another of Grushka’s patients, Maria S., a retail worker in Toronto, said in an email that the most difficult aspect of burning mouth syndrome has been “the pain and thinking that it may be something else or that it will stay forever.” She first noticed burning in the tip of her tongue four years ago, which improved but, she says, “unfortunately it seems to keep coming back.”
For Greg, the burning pain has lessened since he began taking medication in the fall. But even when an oral phantom is not overpowering, it can get in the way of normal life. “It cuts back on my social behavior in terms of engaging in conversation or being more outgoing because I’m aware of what’s going on with my tongue; it’s distracting me,” he reflects.
Over time, the phantom sensation has morphed from burning to dryness and roughness. “You want things to go away quickly; this is not going to go away quickly,” he says. “You have to be patient with it, I guess.”