Bad Taste From the Back of Your Mouth? It Could Be an Infected Wisdom Tooth
Most people notice the taste before they notice anything else. It sits at the back on one side, it does not go away after brushing, and it returns within an hour of using mouthwash. Sometimes there is a slight ache, sometimes nothing at all.
That combination — localised, persistent, unresponsive to cleaning — points strongly towards something trapped and infected rather than a general hygiene issue. In the late teens and twenties, the most common cause is a wisdom tooth that has come through only partially.
This article explains why that happens, what the taste actually is, and which symptoms mean you should be seen the same day rather than waiting.
Can an Infected Wisdom Tooth Cause a Bad Taste?
Where does the taste come from?
Yes, and it is one of the more characteristic symptoms. A partially erupted wisdom tooth has a flap of gum overlying part of it, and beneath that flap is a pocket that a toothbrush cannot reach. Food debris and bacteria collect there. As the bacteria break down trapped protein, they release volatile sulphur compounds — the same family of compounds responsible for the smell of decay — and if pus is forming, that discharges into the mouth as well. The taste is the product of that process draining out from under the flap.
Why Wisdom Teeth Are Prone to Infection
Partial eruption. A wisdom tooth that has come through only part way is the classic setup. The gum flap over it, called an operculum, creates a pocket that is warm, moist, low in oxygen and impossible to clean properly. It is close to an ideal environment for anaerobic bacteria.
Impaction. Where there is not enough room at the back of the jaw, a wisdom tooth may be angled forwards into the tooth in front, lie horizontally, or remain buried. Angled teeth create a food trap between themselves and the second molar, and that space is prone both to infection and to decay on the back of the healthy tooth in front.
Access. Even fully erupted wisdom teeth sit at the very back of the arch, where the cheek is tight, the toothbrush is at an awkward angle and the gag reflex is easily triggered. Plaque control is genuinely harder there for almost everyone.
Timing. Wisdom teeth typically erupt between the late teens and mid-twenties — often a period of irregular routines, and often after orthodontic treatment has finished and attendance has become less regular.
Understanding Pericoronitis
Pericoronitis is inflammation of the soft tissue around the crown of a partially erupted tooth, and it is the specific condition behind most of these symptoms.
The sequence is straightforward. Bacteria colonise the space beneath the operculum. The body mounts an inflammatory response, and the flap swells. Because it swells, it is more likely to be bitten by the opposing tooth, which traumatises it further and increases the swelling. That in turn narrows the opening and makes drainage worse, so bacteria accumulate faster. It is a self-reinforcing cycle, which is why the condition tends to worsen over a few days rather than settle.
Acute pericoronitis produces pain, swelling, a bad taste and often difficulty opening the mouth fully. Chronic pericoronitis may produce little more than the intermittent taste and mild soreness, flaring periodically — often when you are run down, unwell or under stress.
Signs and Symptoms
• A persistent bad or metallic taste from one side at the back
• Bad breath that does not respond to cleaning
• Tenderness or throbbing at the back of the jaw
• Red, swollen gum tissue over or behind the last tooth
• Pain when biting, if the flap is being caught by the upper tooth
• Discharge of pus when the area is pressed
• Difficulty opening the mouth fully — this is called trismus and is a significant sign
• Swollen, tender glands under the jaw
• Earache or pain radiating along the jaw on that side
• Fever or feeling generally unwell
Our page on wisdom tooth pain covers the symptom picture in more detail.
Other Possible Causes of a Bad Taste at the Back
Wisdom teeth are the most likely explanation in a young adult, but not the only one:
• A dental abscess draining through a sinus tract onto the gum
• Advanced periodontitis with deep pockets around the back molars
• Decay under an old restoration, or a lost crown or filling leaving a cavity that traps food
• A cracked tooth with bacterial ingress
• Tonsil stones, which produce a similar sulphurous taste but are usually felt further back and more centrally
• Sinus or nasal problems, and post-nasal drip
• Reflux, some medications and dry mouth
Our article on whether persistent bad breath is a gum problem explains how to distinguish the common causes.
When Professional Dental Assessment May Be Needed
Arrange an appointment if:
• The taste has persisted for more than a few days
• There is tenderness, swelling or discharge at the back of the mouth
• You have had repeated flare-ups in the same area
• You are biting the gum behind your back teeth
• A wisdom tooth is partially through and difficult to clean
Seek urgent care the same day if you have facial swelling, fever alongside the pain, difficulty opening your mouth more than a couple of centimetres, or pain that is worsening rapidly. Spreading infection in this region can become serious. Difficulty swallowing or breathing requires emergency medical attention rather than a dental appointment. Our emergency dentist page explains how to be seen quickly.
Treatment Approaches
Managing the acute episode. The area is irrigated to flush debris from beneath the flap, and the occlusion is checked to see whether the upper tooth is traumatising it. Antibiotics may be prescribed where there is spreading infection, systemic involvement or facial swelling — but they are an adjunct, not a solution, because they do not remove the pocket that caused the problem. Symptoms very commonly return once the course finishes if nothing else changes.
Operculectomy. Where the tooth is well positioned and likely to erupt fully, the gum flap can be removed surgically so the pocket is eliminated. This is appropriate in a minority of cases and the flap can regrow.
Removal of the opposing tooth. Occasionally an upper wisdom tooth is over-erupted and repeatedly biting the lower flap. Removing it can settle the situation without touching the lower tooth.
Wisdom tooth removal. Where the tooth is impacted, repeatedly infected, causing decay in the tooth in front, or has no functional role, extraction is usually recommended. This is planned with radiographs and sometimes a CBCT scan to assess the relationship of the roots to the nerve in the lower jaw. Our wisdom teeth page covers what the procedure involves.
Monitoring. Not every asymptomatic wisdom tooth needs removing. Where a tooth is causing no problems and is cleanable, watchful monitoring at routine appointments is entirely reasonable.
Prevention and Oral Health Advice
• Clean the back teeth deliberately. Angle the brush behind the last tooth and spend time there rather than sweeping past it. A small-headed or single-tufted brush helps considerably.
• Clean between the back molars daily with floss or an interdental brush sized for the space.
• Use an antibacterial mouthwash if advised, aiming it towards the back of the mouth. It is a supplement to brushing, not a substitute.
• Warm salt-water rinses can help settle mild irritation, though they do not treat established infection.
• Attend routine check-ups so wisdom teeth can be monitored radiographically as they develop.
• Keep hygiene appointments, since the back molars are where professional cleaning matters most.
• Act early. A flare-up managed at day one is far simpler than one at day five.
Key Points to Remember
• A persistent one-sided bad taste at the back of the mouth is a common early sign of wisdom tooth infection
• Partially erupted teeth create a pocket beneath a gum flap that cannot be cleaned at home
• Pericoronitis is self-reinforcing — swelling worsens trapping, which worsens infection
• Antibiotics settle symptoms but do not remove the underlying pocket
• Difficulty opening the mouth, facial swelling or fever require urgent care
• Not all wisdom teeth need removing; asymptomatic, cleanable teeth may simply be monitored
The NHS page on wisdom tooth removal explains when extraction is considered and what it involves.
Frequently Asked Questions
1. Will the bad taste go away on its own?
An episode of pericoronitis can settle temporarily, particularly if the trapped debris flushes out, and many people find symptoms come and go. The pocket beneath the gum flap remains, though, so recurrence is common. Repeated episodes are the usual reason removal is eventually recommended, and each flare-up carries the risk of becoming more severe than the last.
2. Can I treat an infected wisdom tooth at home?
You can make yourself more comfortable — warm salt-water rinses, careful cleaning of the area, over-the-counter pain relief taken as directed — but you cannot resolve the underlying problem at home. Do not attempt to open or drain the area yourself. If the taste, swelling or pain persists beyond a couple of days, have it assessed.
3. Do all wisdom teeth need to be removed?
No. Current guidance is against routine removal of wisdom teeth that are causing no problems. Extraction is generally considered where there is recurrent infection, decay in the wisdom tooth or the tooth in front, cyst formation, or damage to adjacent structures. A tooth that is fully erupted, functional and cleanable can usually be left alone and monitored.
4. Is the removal procedure uncomfortable?
It is carried out under local anaesthetic, so you should not feel pain during the procedure itself, and sedation is available for anxious patients. Afterwards, swelling, soreness and limited mouth opening for several days is usual and is managed with prescribed pain relief. Experience varies considerably between individuals and depends on how the tooth is positioned.
5. Why does it flare up when I am run down?
Chronic pericoronitis exists in a balance between the bacteria present and your immune response. Illness, poor sleep, stress and anything else that reduces immune resistance can shift that balance, allowing the bacterial load to increase and symptoms to appear. It is a common pattern and one many patients recognise once it is pointed out.
6. Could it be something other than a wisdom tooth?
Yes. Deep gum pockets, an abscess draining onto the gum, decay under an old filling, tonsil stones and sinus problems can all produce a similar taste. This is why an examination with radiographs matters rather than assuming. If you no longer have wisdom teeth, another cause is certain.
Conclusion
A one-sided bad taste at the back of the mouth is a symptom worth taking seriously, particularly if it keeps returning. It usually indicates something trapped that cleaning cannot reach, and in a young adult that is most often a wisdom tooth.
The condition responds well to prompt assessment and becomes considerably more difficult if left. If you have facial swelling, fever or difficulty opening your mouth, that is a same-day problem rather than a next-available-appointment one.
To have the area examined, arrange an appointment at 22 Wimpole St, London W1G 8GQ, or call 020 7183 0692.
Dental symptoms and treatment options should always be assessed individually during a clinical examination.
Dental Disclaimer
This article is for general educational information only and is not professional dental advice, diagnosis, or a treatment recommendation. Information here is general and cannot replace an in-person assessment by a qualified, GDC-registered dental professional. Symptoms, suitability, fees, timelines, and outcomes vary according to individual clinical circumstances. If you have pain, swelling, or other concerning symptoms, seek prompt professional dental care. Always request a written treatment plan and cost estimate before proceeding with treatment.
Written Date: 6 September 2026 Next Review Date: 6 September 2027
Written by Dr Yasha Y Shirazi · reviewed by Dr Yasha Y Shirazi, GDC 195843
This article is general information, not personal clinical advice. For a diagnosis and a plan tailored to you, book a consultation with a GDC-registered dentist.
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