What causes nasal congestion?

Nasal congestion occurs because the linings of your nasal passages become inflamed or swollen, making it more difficult for air to pass through them. This is what creates that ‘stuffy’ or blocked feeling. Your body may also produce more mucus than usual, causing a runny nose as well as a blocked one.2 While it can be irritating, in the majority of cases nasal congestion isn’t serious and causes nothing more than some discomfort.1 Depending on the cause of your stuffy nose, you may also experience sinus congestion at the same time.

What causes nasal congestion?

Anything that irritates your nasal passages can cause congestion, but the most common triggers are: 3, 4Allergies or hay fever (‘allergic rhinitis’)5 Cold and flu viruses Sinus infection Exposure to irritants such as chemicals, smoke or perfume, Dry, cold air, Certain medications (such as those used to treat high blood pressure)Hormonal imbalances (such as during pregnancy).

How Long Does Nasal Congestion Last?

Most cases of nasal congestion caused by a virus will resolve. For adults, speak to your doctor if:2 Your nasal congestion gets worse or symptoms last more than seven days.You have a high fever. Your nasal discharge is yellow or green and you also have sinus pain or fever (this may be a sign of bacterial infection)You have blood in your nasal discharge, or a persistent clear discharge after a head injury.For children, seek medical attention if:2 Your child is younger than two months old and has a fever.Your baby's runny nose or congestion causes trouble nursing or makes breathing difficult.

How Can I Prevent Nasal Congestion?

You can reduce the risk of catching viral infections like the cold or flu by washing your hands frequently, avoiding any close contact with people you know are sick, and keeping up a healthy lifestyle – meaning lots of sleep, a nutritious diet and daily exercise.8 However, other causes of nasal congestion, such as allergies, may require specific medication or treatments.5

What Is a Runny Nose?

If you are experiencing a runny nose, you’re likely encountering a mucus buildup that drips out of your nose.13 If you have nasal congestion, you may experience a runny nose.13

How Do You Know if it’s a Cold or Allergies?

If you’ve been trying to figure out whether what you’re experiencing is due to an allergy or a cold, you may need to consider your symptoms and when you experience them. Learn the difference between allergy vs cold symptoms and treat them accordingly with this guide from Theraflu.

Brunette woman in a yellow jacket is blowing her nose, unsure whether she has an allergy or cold.

Key Takeaways

Symptoms between colds and allergies overlap. Both can produce sneezing, congestion, and a runny nose, making it difficult to distinguish between them.⁴
Unique symptoms can help you tell them apart. Fever and sore throat are more common with colds, while itchy eyes are typical of allergies.⁴
A decongestant nasal mist can help. Get fast-acting relief with Theraflu Severe Congestion Relief Nasal Mist.

What Causes Allergies

An allergy is an outsized immune reaction to a substance that is usually not harmful.¹ Your immune system will typically protect the body against harmful substances like bacteria and viruses; it will also react to foreign substances known as allergens.¹

What Are Common Allergens?

Someone with an allergy may be affected by allergens through skin contact, consuming something, inhaling something, or being injected.¹

Common allergens include:¹

Insect venom
Pollen
Pet dander
Animal scratches
Latex
Medication
Certain foods
Dust
Mold or Mildew

For people with allergies, the immune system will react to allergens by releasing chemicals such as histamine, which prompt allergy symptoms.

How Do Allergens Affect Us?

Commonly, allergy symptoms will affect the part of the body that has come into contact with the allergen. For example:¹

If you scratch a cat and then touch your eyes, you may have itchy, watery or red eyes as a result.
Eating peanuts when you have a peanut allergy may result in a life-threatening reaction where your throat swells up and restricts your airway. Other allergic responses to food may be less severe: nausea, cramping and abdominal pain.
Inadvertently wearing latex gloves when you have a latex allergy can cause a skin rash or hives.
Going outside during Springtime can cause you to inhale pollen, which can cause a stuffy nose or excess mucus.

What Causes a Common Cold

There are over 200 different viruses that can cause a common cold, with the most common being the rhinovirus.² Once infected, a cold can affect your nose, sinuses, throat and windpipe, and can spread easily, especially when people are in close contact like homes, schools and workplaces.²

What is the Rhinovirus?

Rhinoviruses are viruses that affect the nose and are the most frequent cause of the common cold.³ These viruses can spread from person to person all year long, but are most common during the early fall or spring.³ There are currently no immunizations to prevent an infection from a rhinovirus.³

Preventing the Cold

Colds are highly contagious, they can spread easily from person to person.² For a person to become infected, the virus must penetrate the moist tissues of your eyes, mouth or nostrils.² Being near an infected person who is coughing means you may breathe in some of their droplets of fluid containing the virus.²

Thankfully, there are a few ways to prevent a cold:²

Wash your hands. Wash them frequently, especially when you’re preparing or eating food, using the restroom, wiping your nose or coming into contact with someone who appears sick.
Don’t touch your face. The virus can spread from your hands to your eyes, nose and mouth.
Clean frequently used surfaces. A virus can live on a commonly used surface like a counter or a doorknob and then transfer to your hand, which may then touch your face.

Allergy vs. Cold Symptoms

Despite colds and allergies being caused by different things, they have a few similar symptoms. Thankfully, you can usually tell whether you’re experiencing the symptoms of a cold or a seasonal allergy by the type of symptoms you have and how often they show up.⁴

While there is a fair amount of overlap between the symptoms, there are also a few key differences: seasonal allergies are rarely accompanied by the sore throat and fever that may come along with a cold.⁴

We’ve created this helpful chart to help you learn whether you have an allergy or cold, based on your symptoms:⁴

Symptom	Cold	Allergy
Fever	Sometimes	Never
Itchy Eyes	Rare	Common
Sneezing	Common	Common
Runny Nose	Common	Common
Nasal Congestion	Common	Common
Cough	Common	Rare
Sore Throat	Common	Rare

Managing Nasal Congestion from Cold and Allergies

Nasal congestion is a common symptom of both the common cold and seasonal allergies, but thankfully it can be treated the same way no matter what’s causing it. Try using a decongestant to help relieve a stuffy nose.¹

Get fast-acting relief from severe nasal congestion with Theraflu Severe Congestion Relief Nasal Mist. You’ll breathe better at the push of a button, whether you’ve got a cold or seasonal allergies, thanks to an ergonomic design with a side button that delivers a comfortable mist that unblocks in seconds.

Learn more about the differences between a cold, flu and allergies with this guide from Theraflu.

References

1. What Are Allergies. Penn Medicine. https://www.pennmedicine.org/for-patients-and-visitors/patient-information/conditions-treated-a-to-z/allergies#. Accessed 5/10/25.

2. Common Cold. Cleveland Clinic. https://my.clevelandclinic.org/health/diseases/12342-common-cold. Accessed 5/10/25.

3. Rhinoviruses. Center for Disease Control. https://www.cdc.gov/rhinoviruses/about/index.html. Accessed 5/10/25.

4. Cold or allergy: Which is it? Mayo Clinic. https://www.mayoclinic.org/diseases-conditions/common-cold/expert-answers/common-cold/faq-20057857. Accessed 5/12/25.

How Do You Know if it’s a Cold or Allergies?

Key Takeaways