Before 2020, you might not have worried much about a tickle in your throat or a little tightness in your chest. But that’s changed.

Now even slight signs of a respiratory bug might make you wonder if it’s the start of COVID-19, the illness that has become a pandemic.

How do you distinguish one illness from another? It’s complicated.

“Many of the symptoms overlap. For example, it’s very hard for me clinically, as a physician, to be able to look at someone and say it’s COVID-19 or it’s influenza,” says Dr. Ashish Jha, former director of the Harvard Global Health Institute and now dean of the Brown University School of Public Health.

Don’t jump to conclusions if you start to feel sick. Learn the hallmarks of common illnesses and how they differ from COVID-19, so you can take the appropriate action.


COVID-19 is an extremely contagious respiratory illness caused by a type of virus (a coronavirus) called SARS-CoV-2. It’s a cousin of the common cold, but its potential consequences are far more serious: hospitalization, lasting complications, and death.

Hallmarks: Loss of taste and smell (in the absence of nasal congestion), fever, cough, shortness of breath, and muscle aches.

Other potential symptoms: Sore throat, diarrhea, congestion, runny nose, chills, shivering, headache, fatigue, and loss of appetite.

Note: Some infected people don’t have any symptoms of COVID-19, but they’re still contagious.


Influenza (flu) is a highly contagious respiratory infection caused by the influenza A, B, or C virus. The U.S. flu season typically lasts from October to March, but flu is present year-round.

Hallmarks: Fever, muscle aches, and cough.

Other potential symptoms: Sore throat, diarrhea, congestion, runny nose, chills, shivering, headache, fatigue, loss of appetite.

Different from COVID-19: Flu usually does not cause shortness of breath.

Common cold

The common cold (viral rhinitis) is an upper respiratory infection that can be caused by any of hundreds of different viruses (including coronaviruses or rhinoviruses). It’s usually mild and resolves within a week.

Hallmarks: Congestion, runny nose, cough, and sore throat.

Other potential symptoms: Fever, muscle aches, and fatigue.

Different from COVID-19: A cold does not cause shortness of breath, body aches, chills, or loss of appetite, and it usually doesn’t cause fever.

Seasonal allergies

A seasonal allergy isn’t a virus; it’s caused when the immune system responds to a harmless non-human substance, like tree pollen, as if it were a dangerous threat. Allergies are typically seasonal, lasting for weeks or months, depending on the allergen in the air (mold is the common allergen in the fall and winter).

Hallmarks: Runny nose, itchy eyes, sneezing, congestion.

Other potential symptoms: Loss of smell from congestion.

Different from COVID-19: Allergies do not cause fevers, coughing, shortness of breath, muscle aches, sore throat, diarrhea, chills, headaches, fatigue, or loss of appetite.


Asthma is a chronic lung condition caused by inflammation in the air passages. Airways narrow and make it harder to breathe, which can cause concern that it might be COVID-19. “Asthma can be triggered by a cold or influenza, but it’s a separate condition,” Dr. Jha says.

Hallmarks: Wheezing (a whistling sound as air is forcibly expelled), difficulty breathing, chest tightness, and a persistent cough.

Other potential symptoms: A severe asthma attack can cause sudden, extreme shortness of breath; chest tightness; a rapid pulse; sweating; and bluish discoloration of the lips and fingernails.

Different from COVID-19: Asthma does not cause a fever, muscle aches, sore throat, diarrhea, congestion, loss of taste or smell, runny nose, chills, shivering, headache, fatigue, or loss of appetite.

What you should do

Don’t be a hero and try to tough out an illness. Call your doctor to report any concerning symptoms, especially those of COVID-19 or flu; you may need a test and treatment.

“It’s a different era from when you didn’t want to bother your doctor,” Dr. Jha says. “Don’t deny yourself care. Your doctor would never want that. And the earlier you call, the sooner you can be treated if you need it.”


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