If you get sudden onset of congestion and it is infrequent, the most likely cause would be a viral infection. Viral infections, such as the common cold, are highly contagious and can occur at any time of the year, though they are more common in the wintertime. Not all colds "act" the same. They can be of more or less severity. They can start in the nose or the throat or the chest and they usually spread to involve other regions.

Clues that you have a viral infection are:

Sudden onset and usually feel slightly tired
Large amounts of nasal drainage, frequent blowing
Usually no pain
Prominent congestion and airway obstruction
Usually both sides of your nose are involved
Often people you have been in contact are sick with "the crud"
Symptoms usually are improving by day 5 or 6 and generally are fully cleared before 2 weeks
Minimal relief from antihistamines

Other causes of sudden onset of congestion include acute allergic attacks, and acute bacterial sinus infections.

Acute allergies are usually seasonal and are related to specific pollen blooms or related to exposure, such as disturbing garden material with the release of mole spore. Rummaging through mold-infested material or being around pets that you are allergic to or other situations that can instigate an acute allergic reaction. Acute allergic reactions are characterized by sneezing, itchy eyes, and copious clear drainage, they usually resolve in a couple of days after the exposure has ceased.

If the congestion is infrequent, but comes at the same time every year, consider seasonal allergies. Seasonal allergy flare-ups occur when people have an allergy to a specific pollen and when that pollen blooms, suddenly. Ragweed is one of the most common blooms, but other pollens can also be responsible. Sudden allergy flare-ups from pollen are called "hay fever." Hay fever is not usually caused from hay, and there is usually no fever associated with it. The term hay fever refers to a sudden onset of nasal congestion, itchy eyes, sometimes cough and throat symptoms and is associated with a specific sudden pollen bloom.

Clues that your problem is allergic:

Onset takes several days unless you have some prominent exposure to allergens, like cleaning some musty garage or doing garden work
Sneezing itching and congestion usually affect your nose first and foremost
Usually no pain
Eye itch is common with acute allergies
Usually both sides of your nose are involved
No obvious exposure to people who are sick
Symptoms may come and go depending on if you are inside or outside
Significant relief from antihistamines

Acute bacterial infections often follow the common cold or an allergy flare up. They are frequently just on one side and they frequently cause facial pain or sinus headaches. Cloudy or colored drainage is common and in children cough is the most common symptom.

Clues that you have a bacterial infection:

A cold or allergy seems to be improving, but then gets worse again
One side more involved than the other
Sinus or facial pain, or pain in upper teeth
Thin yellow or green drainage
Not improving after a week
An odor is sometimes noticed
Headaches in people not prone to headaches
Sometimes a cough from post nasal drainage

What to do ?

If this sounds like your situation. First, consider the possibility of that you have a viral infection, see treating colds with OTC medicines. For some reason, people underestimate the number of colds that they suffer each year and prefer to believe that the problems are allergic or of other origin.

If you are pretty sure that it's not a cold, try OTC allergy medicines, use them consistently for a week or so, if they work, some are indicated for long term use if needed. If that doesn't help, a visit to the doctor may be in order. If your problem is frequent and hasn't responded well to OTC medicines, it is time to find out what is going on.

Bacterial infections and difficult to treat allergies can benefit from prescription medicines.  

When congestion is a frequent but not persistent problem, it is often from either allergic rhinitis, flare-ups of chronic sinusitis, or frequent viral infections. Let us consider the difference between these common causes of frequent sudden onset, brief duration nasal congestion.

Frequent Viral Infections

Some people are prone to frequent viral infections. The common cold is one group of viral infections. On most occasions, patients will be doing just fine and then suddenly develop nasal congestion, nasal airway obstruction, clear drainage, sometimes sore throat and sometimes a cough. In adults, there is usually no fever. There are hundreds of types of viruses and they can each product slightly different symptoms. The symptoms of viral infections almost always are on both sides of the nose. They are sometimes associated with a feeling of malaise or a general body-feeling of illness, and they rarely include significant facial pain. It is possible to have some nasal drainage or discharge that is slightly cloudy with viral infections, but more often the drainage is clear.

The average adult gets about two viral infections per year. They are more common in people who are exposed to young children. School teachers, daycare workers and parents with young children are at high risk. Sometimes, it is possible to have a run of "bad luck" and get more than one viral infection, one after the other. It can be hard to differentiate this fairly common situation from an isolated more long-term problem, such as a bacterial sinus infection. People who are at risk for frequent viral infections can benefit from considering just how such infections are spread and taking measures to reduce their spread.

Allergic Rhinitis

"Allergies" are a common cause of congestion and in some people this can be a frequent event. In addition to congestion, patients often have sneezing, itchy eyes, and clear drainage. Allergic rhinitis occurs when inhaled particles that you are allergic to cause an inflammatory reaction on the mucous membranes of your nasal passages. Those particular things that you are allergic to determine when you will have problems and how severe the problems will be. The incidence of allergic rhinitis has been estimated at somewhere between 20% and 40% of people. Not all patients with allergic rhinitis have severe or frequent symptoms. Reactions to cigarette smoke, fumes and odors do not usually represent true allergic reactions, but they can cause similar symptoms by direct irritation or by stimulating certain nerves in the nasal passages. These exposures are usually obvious to the patient.

If you are allergic to mold spore or dust mite, you can have reactions anytime of the year. Sudden flare-ups can occur when you are exposed to large amounts of the agent that you are allergic to. Dust mites are especially dense in carpets, bedding and draperies. Mold spores are especially dense in house plants, flower beds, old magazines and books, objects stored in humid conditions, and anywhere that is frequently damp and where the air does not circulate well.

If the congestion is frequent and comes at the same time(S) every year, consider seasonal allergies. Seasonal allergy flare-ups occur when people have an allergy to a specific pollen and when that pollen blooms, suddenly. Ragweed is one of the most common blooms, but other pollens can also be responsible. Sudden allergy flare-ups from pollen are called "hay fever." Hay fever is not usually caused from hay, and there is usually no fever associated with it. The term hay fever refers to a sudden onset of nasal congestion, itchy eyes, sometimes cough and throat symptoms and is associated with a specific sudden pollen bloom.

Chronic Sinusitis

Chronic sinusitis is one of the most common problems to cause persistent nasal congestion but it can also be a cause of intermittent congestion, ie congestion that flares up and cools down.  It is not always clear why people with chronic sinusitis have flare-ups and cool-downs. The actual process is termed acute exacerbations of chronic sinusitis.  Patients with acute flare-ups of chronic sinusitis, will often have one side of their nose or sinuses more affected than the other;  sinus pain is frequent and sinus headaches are common. Chronic sinusitis can be from low grade bacterial infections, inflammatory reactions to mold spore, or from physical obstruction of drainage.  Obstruction can be from polyps, cysts, or other anatomic abnormalities.

What to do now?

It can be hard to distinguish between the three possibilities suggested above. If you have young children or work around children it is quite possible that at least some of these events represent acute viral infections. Consider treating them as viral infections. If you are pretty sure that it's not a cold(s), try OTC allergy medicines, use them consistently for a week or so.  If they help, some are indicated for long term use.  Steroid sprays used every day are the single most effective medicine for nasal symptoms of allergy.  See the section on treating chronic problems with OTC medicines.   If things aren't going well, a visit to the doctor may be in order. If your problem is frequent and hasn't responded well to OTC medicines, it is time to find out what is going on.

Tips to avoiding viral infections

Viral infections spread when microscopic amounts of nasal secretions or saliva are passed from one person to another. Droplets in the air from sneezes or coughs are one of the ways such secretions can be spread. It is likely that a more common way that viral infections are passed is when you touch the surface that someone with a virus has touched and then later spread the virus to yourself by touching your mouth, your nostril, or rubbing your eyes.

There are some important issues to consider that can help reduce the frequently of catching viral infections, especially when surrounded by persons who are sick, when in crowds where it is likely that there are persons who are sick, or during those times of the year when viral infections are quite common. You should avoid touching your face with your hands unless you have just washed your hands or if you need to scratch or rub your face, use a Kleenex, a cloth. Washing your hands frequently or using the newly available antiseptic/alcohol gels can be very helpful. It is surprisingly common for people to rub or scratch their eyes. When this becomes necessary, you should either use a Kleenex or the inside surface of your shirt or other garment instead of your hands. It is surprising that for some patients, taking simple precautions such as this, can dramatically reduce their frequency of infections. This is especially the case in school teachers, parents of young children, and those in contact with the public.

Nasal congestion lasting more than 6 weeks

Chronic sinusitis is probably the most common cause of a frequent and constant congestion. Chronic sinusitis is just that, chronic inflammation of the sinus cavities. It can be from chronic low grade bacterial infections, chronic inflammation from mold spore inhalation, and from anatomic abnormalities that interfere with adequate drainage. There are other less common causes also.

Allergies

Allergies can cause constant congestion. The type of allergies that are year round are called Perennial Allergic Rhinitis. To be frequent and year round the "irritant" must be constantly present. Examples of allergens that cause persistent symptoms are dust mite, mold spore, pet dander, and cockroach antigen.

Anatomic abnormalities

It is possible to have only anatomic problems as a cause of constant congestion. Enlarged adenoids, enlarged inferior turbinates, concha bullosa, and nasal septal deviations can all cause constant congestion. To identify these causes, an examination by a specialist is usually necessary.

What to do ?

If this sounds like your situation. First, you should explore the section on treating allergies with OTC medicines and treating Chronic Problems with OTC medicines. Consider a trying some of these recommendations if you haven't already.

If that doesn't help, a visit to the doctor may be in order. If your problem has persisted for 6 weeks, and hasn't responded well to OTC medicines, it is time to find out what is going on. If nothing seems to work, you may have chronic sinusitis and should see a specialist.

Diagnosis of chronic sinusitis

Chronic sinusitis is initially diagnosed by symptoms. Later, to confirm the diagnosis, a CT scan is usually obtained. The initial diagnostic criteria for chronic sinusitis are:

2 or more of these major symptoms:

facial pain or pressure
nasal obstruction or blockage
nasal discharge or purulence or discolored postnasal discharge
hyposmia or anosmia
purulence in nasal cavity

or one of the above and 2 of these

headache
fever (for chronic rhinosinusitis)
halitosis
fatigue
dental pain
cough
ear pain, pressure, or fullness

Of note, facial pain requires another major factor associated with it for diagnosis (facial pain plus 2 minor factors is not deemed sufficient for diagnosis of rhinosinusitis).

The 2003 diagnostic criteria for chronic rhinosinusitis requires the above criteria for longer than 12 weeks or more than 12 weeks of physical findings. In addition, one of the following signs of inflammation must be present:

Discolored nasal drainage from the nasal passages, nasal polyps, or polypoid swelling as identified on physical examination with anterior rhinoscopy after decongestion or nasal endoscopy
Edema or erythema of the middle meatus or ethmoid bulla on nasal endoscopy
Generalized or localized erythema, edema, or granulation tissue (If the middle meatus or ethmoid bulla is not involved, radiologic imaging is required to confirm a diagnosis.)

Imaging modalities confirming the diagnosis include the following:

CT scanning demonstrating isolated or diffuse mucosal thickening, bone changes, or air-fluid levels

OR

Plain sinus radiography revealing air-fluid levels or greater than 5 mm of opacification of one or more sinuses

MRI not recommended for routine diagnosis because of its excessive sensitivity and lack of specificity

In general, plain radiography has low sensitivity and specificity. CT scanning is considered the imaging standard for evaluation of chronic sinusitis

When congestion is primarily one sided

Certain problems are less likely if only one side is involved. For example, you generally expect allergies and viral infections to affect people on both sides of their nose almost equally.

If the problem is one sided and chronic, then the possibilities are very similar to that of chronic congestion that affects both sides.

Crooked nasal septal bones, cysts, polyps, and tumors are examples of anatomic abnormalities. Anatomic abnormalities are a frequent source of one sided chronic congestion. Often anatomic abnormalities can work in concert with infection and allergy to give a one sided problem.

Acute bacterial infections can cause one sided congestion, and if the problem is of recent onset and associated with facial or upper dental pain; acute bacterial sinusitis is likely.

Viral infections can begin on one side, but they usually involve both sides of the nose equally after a couple of days. In patients with a nasal septal deviation, or other anatomic abnormality, viral infections can be more symptomatic on one side.

Some thoughts

When one sided airway obstruction is also present, nasal septal deviations come to mind. This is especially true if there isn't much drainage and the problem is long standing and of consistent severity.

When problems have lingered on one side after an acute illness, one sided chronic sinusitis should be considered.

Mild chronic symptoms with pressure between the eyes can be from a concha bullosa, nasal septal deviation, low grade chronic infection, or occasionally such symptoms originate from different types of headaches.

What to do ? If this sounds like your situation. First, you should explore the section on treating Chronic Problems with OTC medicines. Consider trying some of these recommendations if you haven't already.

If that doesn't help, a visit to the doctor may be in order. If your problem has persisted for 6 weeks, and hasn't responded well to OTC medicines, it is time to find out what is going on. Chronic sinusitis and nasal septal deviations often need the attention of a specialist to diagnose and treat them efficiently.