Flu vs. Allergies: What Are the Differences?

A number of bacteria, viruses, and allergens can cause respiratory symptoms. Unfortunately, every breath you take contains a mixture of all of these, plus other irritants like pet dander, pollution, and mold.

Your nose, throat, and airway are coated with mucous membranes, the body’s natural barriers, which detect, identify, and eliminate these irritants and microorganisms. Reactions like coughing or sneezing are the body’s natural way of propelling bad things out.

Since there are so many particles in the air you breathe, it can be difficult to trace the culprit when it comes to respiratory symptoms like a cough. Instead, you must rely on other symptoms and tests to tell the difference.

Symptoms

Symptoms of the Flu

Symptoms of the flu can vary based on the strain of influenza you are infected with. Viruses don’t just affect your respiratory system. They mount a wide-scale attack on your entire body, typically causing more symptoms than a simple cold or allergic response.

Some of the most common flu symptoms include:

• Fever
• Headache
• General body aches and pains
• Fatigue
• Cough
• Chest pain or discomfort
• Shortness of breath

Nasal congestion, runny nose, and sore throat can sometimes appear with the flu, but these symptoms are more likely to develop with a common cold. Other less common symptoms may include diarrhea and nausea or vomiting.

Symptoms of Allergies

There are many types of allergic reactions, but respiratory allergies—sometimes called seasonal allergic rhinitis or hay fever—are most often compared to cold and flu symptoms.

Common symptoms of respiratory allergies include:

• Stuffy nose
• Runny nose
• Sneezing
• Coughing
• Itchy eyes, nose, or mouth
• Red or watery eyes
• Swollen eyelids

In severe cases, allergies may cause problems like shortness of breath, dizziness, increased heart rate, and other symptoms of anaphylaxis, a severe allergic reaction.

In very rare cases, allergic reactions can lead to nausea and vomiting, but this is more common in food allergies than respiratory allergies. Allergies almost never cause a fever, and if you do have a fever with allergies, it’s most likely from a bacterial or viral infection that’s unrelated to your allergies.

Causes

More than 200 viruses alone are known to cause colds, but there are specific viruses to blame for some infections. Allergies, on the other hand, are not caused by any viruses at all.

Causes of the Flu

Four main types of viruses cause influenza:

• Influenza A and B viruses are the most common cause of human illness and seasonal flu outbreaks. There are numerous subtypes of both influenza A and influenza B, and the most common varieties that are circulating can change from one season to another.
• Influenza C viruses cause milder illness and rarely cause epidemics, a sudden outbreak of a disease in a certain geographic area.
• Influenza D usually affects livestock like cattle, not humans.

Causes of Allergies

Allergies are caused by a variety of allergens. Allergens can be any foreign substance that the body has an unusual reaction to. Those that can trigger respiratory allergies typically include:

• Pollens
• Mold
• Dust mites
• Pet dander

Allergies are not contagious or caused by an infectious organism like a virus.

Diagnosis

Diagnosis of any of these conditions begins with an assessment of your symptoms. If you have a cough or other respiratory symptoms that are severe or won’t go away, see a healthcare provider for an accurate diagnosis. Colds are usually diagnosed based on symptoms alone, but flu, COVID, and allergies all have specific tests that can be done.

Diagnosis of the Flu

The flu may be diagnosed in many cases by symptoms alone. If the flu is circulating heavily in the area you live, your healthcare provider may diagnose you with the flu because of your symptoms. Clinical assessment for respiratory complaints may include taking your temperature, measuring your oxygen level, and listening to your lung sounds.

Your healthcare provider may also perform a test for the flu. Rapid tests can provide a result in around 15 minutes, while lab tests take longer but are more exact. Both types of test use a swab to sample secretions in your nose or throat. Some tests can identify the exact strain of the influenza virus that is causing your infection.

Diagnosis of Allergies

Allergies are best diagnosed and managed by your healthcare provider, preferably an allergist. Diagnosis involves a thorough personal and family history, as well as a physical exam. To get the most exact diagnosis, your doctor will perform a skin prick or blood test.

During a skin prick or patch test, you are exposed to a small amount of a particular allergen and observed for a reaction. Blood testing uses a small amount of blood drawn in a laboratory to test for antibodies to specific antigens.

Allergies Doctor Discussion Guide

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Treatment

Treating the flu and COVID involves similar tactics. Like most viruses, treating these infections focuses more on managing symptoms.

Allergy management is similar and focuses on symptomatic relief, although a healthcare provider can offer some options to provide you with a more effective solution.

Treatment of the Flu

Generally, the flu is treated with supportive care, including:

• Medications to reduce fevers
• Cough suppressants
• Lozenges
• Fluids
• Rest

There are also antiviral medications to treat the flu, but not everyone gets sick enough to need them. Sometimes your doctor will offer these medications to you if you are at a high risk of developing complications from the flu. This includes people over the age of 65 or those with weak immune systems.

Flu Doctor Discussion Guide

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Treatment of Allergies

The key to treating allergies is to reduce your exposure. The benefit of a specific allergy diagnosis is that you will find out what triggers your allergies.

You can follow your local pollen counts or avoid things like particular animals that could cause an allergic reaction.

If avoidance is not enough, there are a number of treatments used for allergies, including:

• Antihistamines
• Corticosteroids
• Decongestants
• Immunotherapy

Prevention

Preventing viruses like the flu focuses on the most basic elements of infection prevention:

• Practice good hand hygiene
• Avoid people who are sick
• Avoid going out if you are sick
• Get vaccinated

Masking is an effective measure for preventing the spread of respiratory droplets containing the coronavirus. It can also be helpful for preventing the flu.

While you can’t really prevent allergies, you can try to keep them at bay. If you have chronic allergies, your allergist may keep you on maintenance medications to control how your body responds to allergens.

You may also want to practice precautions like:

• Watch your local pollen counts
• Consider air filtration, and change filters as needed
• Use air conditioning instead of fans
• Keep windows closed when pollen counts are high
• Wash your hair before you go to bed
• Wear protective clothing when doing yard work or pet care
• Change clothes after exposures
• Consider wearing a mask during activities like mowing the lawn
  

Summary

Even though the flu, COVID-19, and allergies all cause similar symptoms, allergies are more likely to cause runny nose, and the flu and COVID-19 can cause symptoms that affect different parts of your body, such as body aches and fever.

The flu and COVID-19 are both caused by viruses, while allergies are triggered by certain substances that you are allergic to, such as pollen. Viral infections like the flu and COVID-19 are usually treated with supportive care, while the best way to treat allergies is to avoid your allergens.

A Word From Verywell

Colds, the flu, COVID, and allergies can be hard to tell apart—even for healthcare providers. This is why a number of tests have been developed to help accurately diagnose these conditions.

If you have a cough that is severe or won’t go away, or your symptoms get better and then return, see a doctor for an official diagnosis. Having a diagnosis will help you find a treatment that works best for your condition.

If you experience dizziness, shortness of breath, or chest pain with any of these conditions, you should seek immediate medical care.

Frequently Asked Questions 

Does COVID make you sneeze?

COVID can make you sneeze, but sneezing is more common with allergies than with viral infections like COVID.

Can you use cold and flu medicine for allergies?

Decongestant cold and flu allergies may be used to help treat allergies, but an allergist can recommend a more targeted treatment that may better manage your allergies without the side effects of cold and flu medications.

Are COVID symptoms different from allergies?

Allergies almost never cause a fever, but fever is a common symptom of COVID, along with a loss of taste and smell.

Can you have a fever with allergies?

Allergies really never cause fevers. If you develop a fever alongside your allergies, it is likely from another cause, like a secondary infection such as pneumonia.