What's the difference between a cold and the flu?

Colds and the flu are two incredibly common respiratory infections. Each calendar year, the average American adult gets around two to three colds, while approximately 8% of the population catches the flu as it circulates between about October and May.

In some ways, it is easy to confuse the common cold with the flu. After all, they're both contagious respiratory illnesses, and they share many symptoms, such as headache, sore throat and cough. However, there are important distinctions between these two illnesses, and the differences affect how each is diagnosed and treated.

So how is the common cold different from the flu?

First, colds and the flu are caused by different viruses. More than 200 respiratory viruses can cause colds. These include rhinoviruses, adenoviruses and non-rhinovirus enteroviruses, as well as some types of coronaviruses. The flu, in contrast, is caused only by influenza viruses. Most commonly, it's caused by the two main types of viruses that cause seasonal flu epidemics in humans: influenza A and B.

The commonly used nickname for the infection — "the flu" — is short for "influenza."

Related: How do people die of the flu?

The viruses that cause colds and the flu also vary slightly in the regions of the body they infect. A cold is a type of upper respiratory infection, Dr. Angela Branche, an associate professor of medicine at the University of Rochester, told Live Science. This means it affects the top portion of the respiratory system: the nose, mouth, sinuses and throat.

When you get a cold, you'll most likely experience a blocked or runny nose, a cough and sneezing. These symptoms are generally mild, and they come on gradually and often go away on their own within a week, without the need for medication. During that time, you may feel unwell but you can usually continue with daily activities. That said, the Centers for Disease Control and Prevention advises avoiding other people while your symptoms persist, to avoid spreading your cold to them.

Flu, on the other hand, usually affects both the upper respiratory tract and the lower respiratory tract, which includes the windpipe and the lungs, and it can also impact other organs. Symptoms of the flu are generally more intense than those associated with colds, and they come on more abruptly.

Patients with the flu may experience additional symptoms, such as fever, chills and body aches, and in severe cases, the infection can lead to serious health problems, including pneumonia and other complications that require hospitalization. Such complications can also happen with colds, but they are much less likely.

Colds and the flu also differ in the way they're diagnosed. Typically, doctors only need to conduct a physical exam and gather the medical history of a patient to determine if they have a cold. A specific test, such as one that requires a nasal swab, is needed to definitively diagnose the flu. In this case, samples of fluid from the nose are analyzed to see if they are laden with influenza viruses.

What's more, some products can now test for the flu and the virus behind COVID-19 at the same time. This is useful because COVID-19 and the flu can also cause some of the same symptoms, but they require different treatments.

Neither the flu nor a cold can be cured with medicine. However, specific drugs can help alleviate a patient's symptoms and shorten the length of time a person has them.

People with a cold may take nasal decongestants or pain relievers, such as ibuprofen (Advil or Motrin) or acetaminophen (Tylenol), Branche said. For the flu, antivirals like oseltamivir (Tamiflu) can reduce the duration of infection by about a day. For people with very severe flu infections, Tamiflu can also lower the risk of death if provided early in the infection.

There is no vaccine against colds, but there is a seasonal vaccine against the flu. With rare exceptions, the CDC recommends that everyone ages 6 months and older get vaccinated every flu season. This vaccination reduces the risk of developing serious complications or dying from the disease, especially for groups vulnerable to the illness, such as very young children, older adults and pregnant people.

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