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 rather, have a physician examine your sinuses and throat for clues to your malodorous 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 of developing nasal polyps increases.

Symptoms of nasal polyps 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, and your voice. Other nasal polyps symptoms include:

The bad smell that accompanies nasal polyps may be due to the 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 serious side effects than corticosteroid sprays.

In more serious cases, endoscopic surgery may be necessary. In this procedure, the doctor guides a thin, flexible 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 air flow.

Sinus infections come in a few varieties, 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, can be caused by a virus or bacteria.

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 7 to 10 days.

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

  • headaches
  • facial pressure
  • postnasal drip
  • fatigue

Treatments for sinus infections depend on whether they are viral or bacterial. A bacterial infection usually requires antibiotics to cure. Antiviral medication exists, but isn’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.

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, fights infection, humidifies the air you inhale, and keeps 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 gets bad and you start to wheeze, you should see a doctor. If you’ve been dealing with postnasal drip for more than 10 days, seek some medical attention.

If there is blood in your mucus, 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.

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 an earache and an ear infection.

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

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.

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, and that buildup of bacteria can cause both bad breath and a bad smell to come through your nose.

Good oral hygiene, which includes brushing teeth and flossing daily as well as 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), don’t put off getting treatment.

Your tonsils include crevices and folds that can trap saliva, mucus, food particles, and 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.

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

Gargling can sometimes dislodge tonsil stones. Even vigorous coughing can help. In serious cases, 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 will 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.

When you have a bad smell in your nose for more than one week and there’s no external source, you should see your doctor.

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

A buildup of mucus, a sore throat, or other symptoms that linger for more than a few days should prompt a visit to your doctor to identify and treat the underlying issue.

And because an ammonia smell in the nose can signal advanced kidney disease, see a doctor right away if you have that symptom, especially 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 are prone to frequent sinus infections, you may encounter these unpleasant episodes repeatedly.

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