Black hairy tongue: why it happens, and how long it takes to clear

The top of the tongue is covered with thousands of fine projections that give it its velvety texture. A review published in the World Journal of Gastroenterology writes that these projections are normally shorter than 1 millimetre, but that in black hairy tongue they can reach 12 to 18 millimetres in length and 2 millimetres in width. The cause is that the surface layer of the tongue fails to shed normally. The layers that cannot shed build up, the projections grow long like hairs, and fungi, bacteria and debris settle between them.

The colour comes from this build-up. The same review explains that residues of tobacco, coffee, tea and other foods, and bacteria that produce pigment, collect between the projections. Cleveland Clinic also notes that the colour is not always black, and can be brown, green, white or other colours. What you see is not the tongue itself but the layer clinging to the lengthened projections.

Why it happens is also largely known. Cleveland Clinic writes that the two commonest causes are poor oral hygiene and a diet of soft foods, because the projections need friction to shed; hard foods and a toothbrush provide this friction. MSD Manuals also counts the tongue not getting enough mechanical stimulation, and food debris becoming trapped between the projections, as the main cause; it notes that it can also appear after a feverish illness or antibiotic treatment, or with overuse of peroxide mouthwashes, and that it is common in heavy smokers.

There are data from Turkey as well. In a study published in Oral Diseases examining 5,150 dental patients, tongue lesions were strongly associated with smoking, drinking black tea and moderate or poor oral hygiene, and hairy and coated tongue was significantly more common in men. The review reports the overall prevalence of black hairy tongue in this study as 11.3%, 18% in men and 6% in women. This rate was measured in people attending a dental clinic; the review writes that prevalence varies from country to country between 0.6% and 11.3%, so the Turkish figure is at the top of the range.

Medicines deserve a separate mention. The review writes that the medicines most often blamed are antibiotics, but that cause and effect has not yet been clearly established and that older studies were based on oral penicillin preparations no longer in use; some antipsychotic medicines that dry the mouth are also linked with this condition, and Cleveland Clinic adds antidepressants, chemotherapy and radiotherapy to the head and neck to the list. In a paper published in the Journal of International Medical Research, 19 antibiotic-related cases were reviewed, and in all of them the symptoms cleared once the medicine was stopped and the tongue was brushed. In one of the cases in the paper, the blackness appeared 12 days after the antibiotic was started and cleared 8 days after the medicine was stopped and the tongue was brushed three times a day.

The choice of mouthwash matters too. The review writes that long-term use of oxidising mouthwashes containing sodium perborate, sodium peroxide and hydrogen peroxide is associated with black hairy tongue. Cleveland Clinic also recommends using a mouthwash that does not contain peroxide or another oxidising agent. If you regularly rinse with hydrogen peroxide to whiten your teeth or freshen your breath, this habit may be the cause.

The tongue may also not be hairy at all, just stained. In the review, this condition, called pseudo-black hairy tongue, is described as the tongue being stained a dark colour without the projections growing longer; foods, tobacco and medicines containing antibiotics, antidepressants and bismuth can do this. Bismuth is found in some stomach medicines. The way to tell them apart is to look at the texture of the tongue: if the surface is smooth but dark rather than furry like a carpet, and the colour fades quickly after stopping the medicine, it is staining.

What really needs to be told apart is dark colour on the tongue coming from a patch or a lump. In the differential diagnosis, the review lists dark pigmentation of the mushroom-shaped projections on the tip and sides of the tongue, which is more common in people with darker skin; congenital moles and patches in babies; and acanthosis nigricans, which causes well-defined, dark, raised lesions on the top and sides of the tongue and can be associated with an underlying cancer. A review in American Family Physician also writes that growths on the tongue often need a biopsy to tell benign ones from precancerous lesions. If what you see is not a furry layer but a flat, well-defined dark patch, a lump or a sore, you are outside the subject of this page.

The situations in the first list usually clear up with cleaning the tongue and removing the cause. If a point from the second list applies, see a doctor.

You can carry out the first four steps at home. If there is no clear improvement within two weeks, see a doctor for the last two.

1. 1

   Find the cause

   In recent weeks, have you started antibiotics or a new medicine, are you using a peroxide mouthwash or a new toothpaste, has your tea, coffee or cigarette consumption gone up, are you eating mostly soft foods? The review recommends asking about local triggers such as a new toothpaste or mouthwash as well.

2. 2

   Clean your tongue gently every day

   After brushing your teeth and flossing, gently clean the top of your tongue a few times from back to front with a tongue scraper or a soft toothbrush. Cleveland Clinic counts this as the first step of treatment. Do not press hard enough to make it bleed; the aim is to help the lengthened projections shed.

3. 3

   Cut down on the triggers

   Cleveland Clinic recommends cutting down on coffee, tea and alcohol, giving up tobacco and stopping peroxide mouthwashes. If you are eating mostly soft foods, foods that need chewing also provide friction on the tongue.

4. 4

   Ask yourself about a dry mouth

   The review lists a dry mouth among the important predisposing causes. Drink plenty of water; if you take a medicine that causes a dry mouth, tell your doctor.

5. 5

   Examination by a doctor

   Cleveland Clinic writes that the diagnosis is usually made just by looking at the tongue, and that no tests are needed. The doctor looks at whether the surface is really furry, at the location and edges of the patch, and at whether there is a sore or a lump.

6. 6

   Rarely, a biopsy

   Cleveland Clinic notes that if another problem is suspected, a biopsy may be requested, and that this is extremely rare.

Treatment for black hairy tongue is mostly simple; what is done depends on the cause.

The following are wrong decisions often seen with this complaint. We set them out so that you can ask the right questions, whichever doctor you see.

The timings vary with the cause and how quickly it is removed. The sequence below is a general framework.

1. The first few days

   Once daily tongue cleaning starts, the build-up on the surface begins to lessen. In one antibiotic-related case, the symptoms cleared 8 days after the medicine was stopped and the tongue was brushed three times a day.

2. 1 to 2 weeks

   Cleveland Clinic writes that symptoms usually clear within this time. The review also notes that it gets better within days to a few weeks once the cause is removed and the tongue is cleaned.

3. If it is still there after 2 weeks

   For symptoms that last longer, Cleveland Clinic advises seeing a doctor about treatment options.

4. Preventing it coming back

   The review writes that stopping smoking, avoiding alcohol and regular oral hygiene are fundamental to preventing it coming back. Cleaning your tongue should be part of your daily routine, just like your teeth.

We are not giving a single figure here, because black hairy tongue usually clears with nothing more than a tongue scraper and a change of habits; in cases that need a doctor, the scope depends on the cause. These are the items that determine the scope:

Whether it is sorted out at home

Most cases clear with daily tongue cleaning and removing the trigger.

Examination by a doctor

A tongue that does not clear or looks suspicious needs examining; usually no further tests are requested.

Accompanying tooth and gum problems

During periods when oral hygiene has slipped, tartar and gum inflammation also build up; a clean is a separate item.

Rarely, medicine or a biopsy

In cases that do not respond to cleaning or look suspicious, medicine or a biopsy comes into consideration.