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A variety of conditions can cause a foul smell in your nose. Most are temporary and not life threatening, usually related to blocked airways or a sinus infection. A doctor can make a diagnosis and recommend the best treatment.

Whether it’s cooking broccoli, living with pets, driving by a water treatment plant, or finding a leftover that’s been left too long in the fridge, hardly a day goes by when at least one bad smell doesn’t find its way into your nostrils.

But what about bad smells that emanate from your nose?

A variety of health conditions — most of which are related to your sinuses — can trigger a rotten smell in your nose.

Fortunately, most of these foul fragrances are temporary and not signs of a life threating condition. They tend to be indications that mucus or polyps are blocking your airways.

If a bad smell is filling your nose and there are no outward culprits to blame, you may need to look inward.

Or, you may need to have a healthcare professional examine your sinuses and throat for clues to your unpleasant-smelling mystery to start clearing things up.

Here are some likely suspects.

Nasal polyps are soft noncancerous growths that can form on the wall of your nasal cavity or sinuses. These small, teardrop-shaped growths form as a result of chronic inflammation.

If you have asthma, allergies, or frequent sinus infections, your risk for developing nasal polyps increases.

Symptoms of nasal polyps may or may not include a rotten smell in your nose or a dramatically decreased sense of smell and taste.

Nasal polyps tend to be very small, so you may not even know you have them. They may not affect your breathing.

However, large polyps sometimes form.

Or you may have so many small polyps that your nasal passages become blocked, affecting:

  • your sense of smell
  • your ability to breathe through your nose
  • your voice

Other nasal polyps symptoms include:

The bad smell that accompanies nasal polyps may be due to fluid buildup inside the polyps.

The fluid comes from the damp lining of your mucous membrane, which helps moisten your respiratory tract and trap dust and other foreign substances from reaching your lungs.

Nasal polyps can often be treated effectively with prescription corticosteroids, which are medications that can shrink polyps and reduce inflammation.

Usually, nasal corticosteroid sprays, such as fluticasone (Flonase) and mometasone (Nasonex), are tried first.

If they’re ineffective, your doctor may prescribe oral corticosteroids like prednisone, though these drugs are more likely to have more serious side effects than corticosteroid sprays. It is also important to manage the underlying causes of polyps, such as allergies, infections, or asthma.

In more serious cases, endoscopic surgery may be necessary. In this procedure, the doctor guides a thin scope (endoscope) with a tiny lens at one end through the nasal cavity and sinuses.

The endoscope can also remove polyps or any other obstructions that may be impeding airflow.

Sinus infections vary — none of them pleasant — and all of them have the potential to fill your nose with an icky smell. Sinusitis, another name for sinus infection, normally caused by a virus or bacteria.

A fungus can also cause sinus infections. The severity of a fungal infection can range from mild to very serious. Fungi are more difficult for the body to build an effective immune response to compared with bacteria or viruses.

Fungal infections can impair immune function.

They happen more commonly and more seriously in people who are already immunocompromised (have a disease that affects immune function or is on chemotherapy or other drugs that reduce immune response).

Those with chronic sinusitis related to a bacteria or virus may develop fungal sinusitis.

Knowing the cause of your sinus infection is important to planning treatment. You can also have chronic sinusitis, which is a sinus infection that lasts for at least 12 weeks.

Short-term sinus infections are known as acute sinusitis, and they typically last 3 weeks or less.

In addition to a bad smell inside your nose and a reduced sense of smell and taste, symptoms of a sinus infection include:

  • headache
  • facial pressure
  • postnasal drip
  • fatigue

Treatments for sinus infections depend on whether they’re viral or bacterial. A bacterial infection usually requires antibiotics to cure. Antiviral medications exist but aren’t always prescribed.

In many cases, a viral sinus infection will run a similar course with or without medication.

Rest and hydration are recommended regardless of the cause or severity of your infection. Nasal saline rinses can also be helpful to clear congestion.

Smelly mucus in the nose, especially when it thickens and seems to drip incessantly down the back of your throat, is a sign of postnasal drip.

Normally, mucus helps:

  • keep your nasal membranes healthy
  • respond to infections
  • humidify the air you inhale
  • keep foreign particles out of your airways

It mixes with saliva and is swallowed without you being aware of it.

A cold, flu, allergy, or sinus infection can cause mucus to thicken, making it harder for it to drain normally.

Postnasal drip may begin mildly, with no bad smell or impact on breathing. But if the smell worsens and you start to wheeze, you should see a doctor.

If you’ve been dealing with postnasal drip for more than 10 days, seek medical attention.

Along with constant swallowing of mucus, coughing (especially at night) and a sore throat are the other signs of postnasal drip.

In some cases, poorly draining mucus can build up in the middle ear, causing earache and an ear infection.

If there’s blood when you blow your nose, it’s most likely a result of vigorous nose-blowing with dry mucus. If it continues, you should see a doctor immediately. It may only be a sign of a growing infection or a scratch inside your nose, but it’s better to find out sooner than later if it’s something more serious.

Drinking lots of fluids and using a saline nasal spray is helpful. You may also benefit from sleeping with your head slightly elevated and using a humidifier, vaporizer, or nasal saline solution to moisten your nasal cavity.

Shop for humidifiers online.

If those remedies don’t do the job, your doctor may recommend antihistamines (if an allergy is to blame) or a cortisone steroid nasal spray to relieve inflammation.

Shop for antihistamines online.

If a bacterial infection is causing postnasal drip, you will need a course of antibiotics.

When bacteria collect on a tooth, they can eat away at the surface. This is tooth decay. That buildup of bacteria can cause both bad breath and a bad smell to come through your nose.

Good oral hygiene, which includes brushing your teeth and flossing daily as well as scheduling regular dental appointments, are the best ways to prevent tooth decay and tooth and gum problems.

If your dentist has identified a cavity or other problem that needs to be addressed, such as periodontitis (gum disease), try to get treatment as soon as possible.

Your tonsils include crevices and folds that can trap:

  • saliva
  • mucus
  • food particles
  • dead cells

Sometimes the debris can harden into tiny objects called tonsil stones.

Bacteria can feed on tonsil stones, generating a bad smell in your nose and a bad taste in your mouth. Poor oral hygiene and unusually large tonsils increase the risk of tonsil stones, but it’s important to note that plenty of people have tonsil stones with perfectly adequate oral hygiene.

Practicing good oral hygiene and staying hydrated can help reduce the risk of bacterial buildup.

Gargling or flushing the tonsils with a water pick can sometimes dislodge tonsil stones. In serious cases, tonsillectomy, lasers, or radio waves can be used to treat this condition.

This is one condition that can’t be blamed on bacteria or any actual producer of bad smells.

Phantosmia is a hallucination of your olfactory system. You smell odors that aren’t really there, but you think they’re in your nose or somewhere around you.

Phantosmia can develop after a respiratory infection or a head injury. Conditions such as Parkinson’s disease, brain tumors, or inflamed sinuses may also trigger phantom smells in your nose.

For some people, phantosmia resolves on its own. For others, treating the underlying cause of phantosmia may help eliminate the bad smell sensation.

Chronic kidney disease (CKD) is a progressive loss of kidney function.

Your kidneys serve several purposes, including the filtering out of waste products from your blood for removal from the body in urine.

If the kidneys aren’t functioning well, waste materials may build up in the body.

Those materials can produce an ammonia-like smell that you may notice in the back of your nose. You may also have an ammonia-like or metallic taste in your mouth.

This development usually occurs only after CKD has advanced to stage 4 or 5.

At this point, you’ll have other symptoms, such as kidney pain, changes in urine color, and fatigue, so a new ammonia smell probably won’t be the first sign of kidney trouble.

A foul smell with unilateral nasal drainage could be the result of a foreign body trapped in the nasal passage. This is especially common for kids or intellectually delayed adults.

A number of people who have regained their sense of smell during a COVID-19 infection have experienced distorted smells, or parosmia. People have reported that coffee smelled like gasoline, or food smelled like decayed garbage.

Covid-19-related parosmia is thought to occur because of alterations that occur as damaged olfactory receptors regenerate after a loss of smell.

When you have a bad smell in your nose for more than 1 week and there’s no external source, you should see your doctor. If you don’t already have a primary care doctor, our Healthline FindCare tool can help you connect to physicians in your area.

Because a rotten smell in your nose often means you’re also dealing with a sinus infection, nasal polyps, or another condition, it’s likely you also have other symptoms.

And because an ammonia smell in the nose can signal advanced kidney disease, see a doctor right away if you have that symptom.

This is especially true if you have other symptoms such as kidney pain and changes in the appearance and smell of your urine.

Most causes of a bad smell inside your nose are treatable. Your experience with smelly mucus or smelly tonsils may be a one-time event.

However, if you’re prone to frequent sinus infections, you may encounter these unpleasant episodes repeatedly.

Talk with your doctor about how you can lower your risk for nasal and throat problems down the road.