I have bad breath and a strange taste in my mouth. What is causing it?

Bacteria produce the smell. As they break down the protein in food debris and dead cells, sulphur gases are released. These bacteria work in corners without oxygen: in the grooves on the back of the tongue, at the bottom of a gum pocket, between two teeth, inside a decay cavity and under a denture. All five have the same thing in common: neither a toothbrush nor mouthwash reaches them. That is why the smell does not go away.

The most common single source is the back of the tongue. The back third of the tongue is rough; bacteria, dead cells and food debris build up there as a whitish coating. Because saliva flow slows down at night, the smell is at its strongest in the morning. In someone who brushes their teeth but never cleans their tongue, this is the source.

Medically, the most important source is the gum pockets. In a healthy mouth, the gap between the gum and the tooth is one to three millimetres. When inflammation reaches the bone, this gap deepens and its bottom turns into a hollow without oxygen; the bacteria that produce the smell live right there. The pattern is clear: the smell eases for a few hours after brushing, comes back during the day and never stops completely. If your gums also bleed, the source is certain. This disease progresses without pain; the smell is its first warning, and a loose tooth its last.

The third source is decayed teeth, fillings that have opened up at the edges and the area under a denture. Food gets trapped inside a tooth with a cavity, and a toothbrush cannot empty that space. When decay reaches the nerve and kills the tissue, the decaying tissue inside the canal gives off its own smell. An acrylic denture is porous; when it is worn without being taken out at night, a closed surface forms underneath where bacteria and fungi grow. The body of a fixed bridge also sits on the gum, and if the underside is not cleaned with super floss, it smells. This smell is one-sided, always comes from the same area and does not go away whatever your oral care.

Dry mouth prepares the ground for all of this. Saliva washes the mouth and buffers acid; when there is less of it, the mouth cannot clean itself. Hundreds of medicines reduce saliva, led by blood pressure medicines, antidepressants and bladder medicines. The causes outside the mouth come after this: with postnasal drip and sinusitis, the mucus running down the throat gives bacteria a foothold at the back of the tongue; acid reflux leaves a sour taste in the mouth; and in uncontrolled diabetes the mouth dries out and gum inflammation speeds up. The telling sign is this: a smell that comes from the mouth eases for a while after you clean your teeth, while a smell from the sinuses or the stomach is not affected by oral care at all.

Taste is a separate sign. The most common cause of a metallic taste spreading through the mouth is bleeding gums; the iron in blood gives this taste. The taste that really needs attention is a different one: a persistent taste from a single spot, described as salty or like pus, that gets stronger when you touch the area with your tongue. This is inflammation at the tip of a root draining into the mouth through a small opening it has made in the gum. The pain stopping is not healing; it has stopped because the pressure has been released. A sweetish, acetone-like smell on the breath is a different matter. Going without food or a very low-carbohydrate diet causes the same smell; but if you have diabetes and the smell comes with nausea, vomiting, fast breathing or extreme thirst, your blood sugar may have risen dangerously high. That situation gets worse within hours: go to A&E.

This distinction becomes clear after an examination, pocket measurements and an X-ray. Seeing yourself in the second list does not mean that tooth will go today; it only changes the option we will discuss.

This sequence is for diagnosis, not treatment. By the end, you know which spot the smell is coming from, whether any part of it is urgent and which step will really deal with it.

1. 1

   First, we separate out what is urgent

   If the smell comes with swelling in your face or under your eye, a high temperature, difficulty opening your mouth or difficulty breathing, the inflammation has spread beyond the tooth; go to A&E the same day. If there is a sweetish, acetone-like smell on your breath and it comes with nausea, vomiting, fast breathing or extreme thirst, the place to go is not a dentist but A&E. If none of these apply, the smell is not urgent, but it will not go away on its own either. A salty or pus-like taste from a single spot is not a matter for A&E, but it should not be put off; that tooth needs to be seen within days.

2. 2

   We talk through the history of the smell

   How long it has been going on, whether it changes after brushing, and whether it comes from a single spot or from everywhere all narrow down the source. The list of medicines you take, postnasal drip, acid reflux, smoking and your blood sugar readings matter just as much.

3. 3

   We map your mouth

   We look at the coating on the back of the tongue, pocket measurements taken at six points around every tooth, bleeding, the edges of old fillings, the area under a denture and any small blister on the gum. A deep, narrow pocket around a single tooth is the first sign of a root fracture.

4. 4

   X-rays and, if needed, a CBCT scan

   A panoramic X-ray shows the bone level, what is under the supporting teeth of a bridge and the dark area that points to inflammation at the tip of a root. Decay between the teeth often cannot be made out on a panoramic X-ray; for that we take bitewing X-rays. For root fractures that do not show up on a plain X-ray, we use a cone beam CT (CBCT) scan.

5. 5

   Send us your X-ray

   If you have a panoramic X-ray or a CBCT scan, send it through the form; we write to you within 24 hours about whether the source of the smell can be seen and which options are on the table. The final decision is made after an examination and pocket measurements.

These are not competing options but steps taken in order, starting with the simplest. The important point is this: each step only deals with its own source; it does not do the job of another.

We are not writing this to frighten you, but so that you can ask the right questions whichever dentist you see. If a dentist does not explain these points without being asked, ask.

The sequence below applies to the route that starts with tongue and interdental cleaning and, if needed, continues with gum treatment and implants. If the source is a single area of decay, the process is much shorter than this.

1. The first three days

   When tongue and interdental cleaning are done regularly, there is a noticeable drop in morning breath. These three days show how much of the smell can be solved at home; the rest is a job for the dentist.

2. Two to three weeks

   After a scale and polish, the gums firm up, the bleeding stops and the smell from the pockets fades. Temporary sensitivity to cold in the first few days is normal; do not stop brushing.

3. Six to eight weeks

   We measure the pockets again. Where pockets have closed, the matter of the smell is closed too; where they have not, surgical cleaning or the future of that tooth is discussed. A smell that continues while the mouth is completely clean points to a cause outside the mouth, and we direct you to an ear, nose and throat specialist or an internal medicine specialist.

4. If extraction and implants were chosen: three clinical days

   In the protocol we use, the implants lock mechanically into the hard basal and cortical layer deep in the jaw. A conventional implant, by contrast, is placed in the upper part of the jaw that shrinks as teeth are lost, that is, the alveolar bone; there, anchorage strong enough to bear load only forms after months of the bone fusing with the implant. That is where the difference comes from. Bone grafting does not come into it, and at the end of three clinical days you leave with your final fixed teeth. We also use it for our patients with diabetes. After that, it comes down to maintenance: the underside of fixed teeth, just like the underside of a bridge, smells if it is not cleaned.

We do not give a single figure on this page: for a patient who comes in with bad breath, the route can end with a single cleaning session or extend to extraction and implants, and the difference between the two is large. We give you the right figure after seeing your mouth and your X-ray. These are the items that determine the price:

What the source is

A scale and polish, root cleaning inside the pockets, a filling, root canal treatment and an implant are different procedures, with different lengths and numbers of sessions. A figure given before the source has been identified is bound to change at the clinic.

How many areas are affected

A single tooth that smells and gum disease that has spread through the whole mouth are costed separately. In the second case, treatment is planned area by area and the number of sessions goes up.

The condition of existing work in your mouth

Bridges that need to be removed and replaced, crowns that have decayed underneath and dentures that do not fit widen the scope. The X-ray and the examination tell us which of them can stay.

Extra surgery and the teeth on the implants

If extraction and implants are the route, the material of the fixed teeth made on the implants and the laboratory work determine the total. We tell you in writing from the start which brand of material we use.