The common cold, influenza (the flu) and COVID-19 are all caused by respiratory viruses and share some of the same symptoms, but they can lead to very different outcomes.

The common cold can be caused by a variety of viruses, including coronaviruses and adenoviruses. Typical symptoms include nasal congestion (a stuffy or runny nose), sneezing, a sore throat and a cough; fever is uncommon. Nasal discharge and phlegm may be thick and white, yellow or greenish in color.

Influenza can cause these symptoms too, but more often it presents with fever or chills, fatigue, headache and muscle or joint aches. Some people, especially children, may have gastrointestinal symptoms, such as nausea or diarrhea. Flu symptoms tend to come on more suddenly and are typically more severe than cold symptoms.

Common symptoms of COVID-19, caused by a new coronavirus named SARS-CoV-2, include fever or chills, a dry cough and shortness of breath. But COVID-19 can be marked by a wide range of other symptoms as well. One of the most distinctive signs of COVID-19 is loss of the sense of taste or smell. Many people have no symptoms.

Common colds usually resolve in about a week without treatment. Most people with influenza or COVID-19 recover within a couple of weeks, but these diseases are more likely to lead to severe complications. Older people are more likely to have severe flu or COVID-19; young children are more likely to have severe flu but are at low risk for severe COVID-19.

People with mild illness can usually manage their symptoms at home with supportive care, including drinking plenty of fluids, getting enough rest and taking over-the-counter medications. These viral illnesses cannot be treated with antibiotics. Seek medical care if you or your child develop a high fever, have difficulty breathing or experience mental confusion.

If you have any of these symptoms, stay home from work or school, avoid close contact with other people, cover coughs and sneezes and take other recommended precautions. Testing is the only way to know for sure whether you have a cold, influenza or SARS-CoV-2. Getting a flu vaccine is more important than ever during the COVID-19 pandemic.