A BURNING feeling on the tongue or roof of the mouth can usually be traced to a steaming cup of tea, or maybe to a hot bake or piece of fish just out of the frying pan. But for some people, particularly postmenopausal women, a debilitating burning sensation in the mouth can develop out of the blue. And then it never leaves.

This condition was once considered one of the many symptoms “nervous” older women invented for themselves. But new research now suggests that it is linked to taste changes in the mouth.

Burning mouth syndrome (BMS) is defined as a constant burning sensation in the mouth that’s usually present in the tongue and often on the palate, but it can be anywhere. It often starts suddenly and then it can continue for months or years. People complain that their mouth feels as though they had been burnt with hot coffee, or had just eaten pepper except it just does not go away.

The burning sensation usually gets worse over the day. It is not too bad in the morning, then it gets worse after the first meal of the day and then it peaks in the late afternoon or by early evening. Once people go to sleep, the pain usually disappears. And then when they wake up in the morning, they feel fine.

And the cycle keeps repeating itself. Very commonly, BMS is associated with a metallic or bitter taste in the mouth that also gets worse over the day. A lot of people complain about dry mouth. But when you look in the mouth and check the flow of saliva it’s normal. These symptoms are often very severe. There have been a lot of studies looking at the psychological impact and if burning mouth syndrome is severe and ongoing, it can cause a lot of depression and anxiety. The pattern of changes is very similar to what’s seen in other people who have chronic pain.

Until recently, the diagnosis of BMS was typically based on the clinical symptoms. It has been a diagnosis of exclusion so that people were tested to see if they had an oral yeast infection or a vitamin deficiency or diabetes. And if they had none of those changes and their mouth looked normal and they had the typical pattern of burning, they ended up with a diagnosis of burning mouth. But more recent studies show the association between burning mouth and taste changes. Remarkably, there is almost a footprint of the disorder—a loss of bitter taste at the tip of the tongue.

We can check the ability to taste sweet, sour, salt and bitter flavours at the front and then at the back of the tongue using a spatial taste-test. So someone with burning mouth syndrome may have normal tastes or somewhat reduced tastes for sour, sweet and salty flavours but the ability to taste bitter flavours, which is located at the tip of the tongue, is often gone.

The theory is that the taste inhibits pain and, if there’s a problem with taste (like loss of bitter taste at the tip of the tongue), there’s a loss of inhibition of the pain fibres, so someone spontaneously begins to produce pain. And the pain is interpreted as burning mouth pain. Another test is performed using a local anaesthetic. When a local anaesthetic is applied to the tip of their tongue where they have the burning, the pain often gets worse instead of getting better.

The disease is most common in women after menopause. One of the reasons that this problem is found in older women relates to the loss of estrogen that occurs during the menopausal period and that causes a loss of bitter taste buds. We do see men with burning mouth, but it’s less common. Sometimes I see younger people with it or even men, but it is usually associated with a benign condition called geographic tongue. Geographic tongue causes inflammation on the surface of the tongue causing red patches that come and go and move around. That might affect the taste buds which then leads to the loss of pain inhibition and burning mouth.

When the bitter taste is lost within the taste bud, the pain fibres surrounding that bud are the ones that experience a loss of inhibition and start becoming painful. An infection, a nutritional deficiency of B12, folate or iron can also damage taste buds.

And just to make it a little bit more complex, the people who are most at risk of developing burning mouth are called super-tasters—people who have the greatest number of taste buds on the tip of the tongue.

This is a genetic difference: some people are non-tasters, some are medium tasters and some are supertasters. Flavours are much more intense for super-tasters, and they have different taste preferences than non-tasters and medium-tasters. Women are much more likely to be supertasters than men. So, most people with burning mouth syndrome are supertasters who have had a taste loss for some reason.

People who do a lot of clenching are at increased risk. They keep their tongue pressed tightly against their teeth at night and they end up with their tongue scalloped. When the clenching is controlled, through medication or the use of mouth guards, they often feel better. In addition, certain conditions such as diabetes, thyroid disease and liver dysfunction have been associated with burning mouth syndrome. While there is no specific drug to treat BMS several medications used for other diseases have been found to give relief.