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What Is the Difference Between Cold and Flu? Symptoms, Causes, Diagnosis, Treatment, and Prevention

November 25, 2019

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Influenza, or the flu, and the common cold can be tricky to tell apart. Both are respiratory illnesses caused by viruses, and they share many symptoms.

The common cold and the flu are both contagious, but cold symptoms tend to be milder and improve within a week to 10 days, according to Mayo Clinic.While most people who get the flu recover in less than two weeks, the symptoms are more severe, and serious complications, such as pneumonia, bronchitis, and sinus or ear infections, can develop, notes the Centers for Disease Control and Prevention (CDC).

Since colds and the flu are caused by viruses, rather than bacteria, antibiotics are not an effective treatment option.

Signs and Symptoms of Cold and Flu

Both the flu and colds affect the respiratory system, though flu symptoms are typically more severe than those of the common cold.

“There are many different viruses that can cause a cold, but most of these viruses cause very similar cold symptoms,” says Aaron E. Glatt, MD, chief of infectious diseases at South Nassau Communities Hospital in Oceanside, New York.

Symptoms that the common cold and flu share may include:

body aches
headache
sore throat
cough
nasal congestion
sneezing

Unlike a cold, the flu is usually accompanied by fever and influenza symptoms tend to come on more suddenly. Chills are common with the flu but not with a cold, per the CDC.

"Run-of-the-mill colds usually make you feel lousy but should not interfere with daily activities," says Stephen Russell, MD, an associate professor of medicine at the University of Alabama in Birmingham.

While most colds don’t require a visit to the doctor, they can turn into something more serious. According to the American Academy of Family Physicians, some warning signs to look for include high fever, shortness of breath, and symptoms that last more than 10 days, continue to worsen, or get better initially but then get worse again.

Learn More About Cold and Flu Signs and Symptoms

Causes and Risk Factors of Cold and Flu

The flu is caused by influenza viruses, but many distinct viruses (most commonly rhinoviruses) can cause a cold.

Common cold symptoms typically develop about one to three days after exposure to cold-causing viruses. These viruses can be spread through the air, personal contact, and respiratory secretions — encounters such as a handshake, touching contaminated objects, and exposure to an infected person’s sneezes or coughs, notes Mayo Clinic.Shouting, singing, or even simply talking can also release contaminated droplets into the air, which can then be inhaled, transmitting the virus, according to Houston Methodist.

Certain populations are more susceptible to getting a cold or the flu, including the very young, older adults, and people with a compromised immune system.

Factors that can increase your risk of becoming infected include:

Age

Children younger than 5 and adults over 65 are at higher risk for developing complications from the flu, according to the CDC.

Season

Seasonal flu activity typically occurs between October and May (flu season), although flu viruses are around all year, per the CDC.

Similarly, most people develop colds in the winter and spring, but they can occur anytime, notes the CDC.

Weakened Immune System

Viruses can more easily infiltrate the body if you have a weakened immune system. Certain chronic illnesses, such as cancer, HIV or AIDS, and autoimmune diseases raise the risk of catching a cold or the flu, according to the CDC.

Smoking

Chronic smoking makes your respiratory system more vulnerable to cold and flu viruses and complications. The American Lung Association reports that cold symptoms tend to be more severe in smokers.Smokers also have a higher risk for severe illness from a flu infection, per the CDC.

Pregnancy

Women in their second or third trimester are particularly susceptible to complications from the flu. “We’re not exactly sure why, but there has always been a question of whether or not the immune system changes during pregnancy,” says Laura Riley, MD, the chair of obstetrics and gynecology at Weill Cornell Medicine and obstetrician-gynecologist in chief at NewYork-Presbyterian Hospital in New York City.

RELATED: 8 Ways to Keep Your Immune System Healthy

What Types of Flu Are There?

There are four types of influenza viruses: A and B, which are most commonly associated with seasonal flu activity and epidemics; C, which is relatively rare and causes mild respiratory illness; and D, which primarily affects cattle, according to the CDC.

Influenza A

There are many subtypes of influenza A viruses, based on two proteins — hemagglutinin (H) and neuraminidase (N) — found on the surface of the viruses. Two strains of influenza A found in human beings are the H1N1 strain and the H3N2 strain.

A novel strain of influenza A (H1N1) virus, known as swine flu because it’s typically spread among pigs, led to a flu pandemic in 2009. Between April 2009 and April 2010, the CDC estimates that there were 60.8 million swine flu cases in the United States, which led to more than 274,000 hospitalizations and nearly 12,500 deaths.The influenza pandemic of 1918 was an H1N1 virus of avian origin.

H3N2 mutates more rapidly than other strains, which can make it particularly resistant to the flu vaccine.

Influenza B

Less common than influenza A, these viruses cause similar symptoms and can lead to seasonal outbreaks. Influenza B is not categorized by subtypes, but there are two strains of the virus: Yamagata and Victoria.

Influenza C

Like influenza A and B, these viruses are found in humans. But influenza C viruses are milder and are not thought to cause epidemics. Seasonal flu vaccines, which contain strains of influenza A and B, do not protect against influenza C viruses.

Influenza D

This strain of influenza is not known to cause illness in humans. A relatively new strain, it primarily affects cattle, though a report published in October 2020 in Current Opinion in Virology notes that it could eventually pose more of a threat to humans.

Duration of Cold and Flu

The duration of a cold or the flu varies depending on the virus involved and your immune system’s ability to fight off infection. That’s why the very young, the elderly, and people with chronic illnesses are most susceptible to viral infections and possible complications.

“The best weapon we have is our own immune system,” says Donald W. Novey, MD, a family and integrative medicine specialist in Poulsbo, Washington. Good nutrition, adequate sleep and exercise, and low levels of stress can bolster the immune system. “A failure on any one of these four points can weaken the immune system and either prolong an existing cold or lead to more frequent ones,” Dr. Novey says.

Cold symptoms typically subside within 7 to 10 days, while the flu typically lasts three to seven days with severe symptoms subsiding after a few days. But some symptoms, like fatigue and cough, can linger for weeks.

People with the flu are most contagious during the first three to four days after their illness starts, but some adults may be able to spread infection one day before their symptoms start and up to seven days after, notes the CDC.

RELATED: How Long Does a Cold or Flu Last?

Complications of Cold and Flu

Most common colds are not severe, but they can worsen or lead to health complications.

“Enteroviruses that are often the culprits in the common cold can cause brain lining inflammation that causes severe headaches, difficulty looking at bright lights, neck stiffness, high fever, and confusion,” says Cameron Wolfe, MBBS, an infectious-disease specialist at Duke University School of Medicine in Durham, North Carolina.

If cold or flu symptoms persist or worsen, the patient may have a secondary or bacterial infection. That can lead to sinus or ear infections, bronchitis, and pneumonia. The flu can also worsen preexisting medical problems, such as triggering asthma attacks in people with asthma.

More rarely, severe flu complications can include heart infections such as myocarditis, and brain inflammation illnesses such as encephalitis.

Learn More About Complications of Cold and Flu

Research and Statistics: Who Gets Cold and Flu?

Most people feel the effects of the common cold or flu every year. Adults average two or three colds each year, per the CDC;and young children may get sick as many as 8 to 10 times a year before they turn 2.

Between 3 and 11 percent of the U.S. population gets a symptomatic flu infection annually, according to the CDC.There is a wealth of data available to track seasonal flu activity, including the CDC and World Health Organization websites, as well as local public health offices. (See the Resources We Love section below.)

Related Conditions of Cold and Flu

Some conditions are related to colds and the flu, meaning you may develop them after being sick, or they may make you more susceptible to catching a virus. These include:

Asthma
Bronchitis
Pneumonia
Ear infections
Sinus infections
Strep throat

What Is the Flu Season Like Where You Live?

The Everyday Health flu map predicts flu severity county by county across the United States so you can plan ahead and take precautions to avoid the flu — both at home and in places where you plan to travel.
By entering your ZIP code, you can find out what influenza conditions may be like in your county in the weeks ahead.

Resources We Love

Favorite Organizations for Essential Information

American College of Obstetricians and Gynecologists (ACOG)

ACOG’s Immunization for Women program provides patients, including those who are pregnant, with up-to-date recommendations and guidelines on treating seasonal influenza and other vaccine-preventable diseases. This trusted source also provides a searchable ob-gyn directory.

Centers for Disease Control and Prevention (CDC)

The CDC’s website presents weekly updates on flu activity nationwide. The site details how the flu may be spreading in each state and which strains of the virus are most prominent. It also contains useful guidelines for the most current treatments and vaccinations.

National Foundation for Infectious Diseases (NFID)

Founded in 1973, the NFID is a nonprofit dedicated to educating the public and healthcare providers about infectious diseases. Its influenza web page provides basic information about the flu and links to sections about influenza in vulnerable segments of the population, such as children and older adults.

State Health Departments

Thanks to this search function on the CDC's website, you can locate your state health department, which can then help you find direct access to your county’s health department. Your local health department will likely provide updated information on flu activity in your area, as well as information on how to access vaccinations.

World Health Organization (WHO)

The WHO’s global influenza website provides worldwide surveillance information on flu outbreaks and what prevention efforts are taking place. It also provides information from its conferences regarding future strategies to combat the flu.

Best Flu Vaccination Information

CDC — Vaccine Safety

The CDC’s flu vaccine page provides up-to-date information on approved influenza vaccines, along with potential side effects.

National Vaccine Information Center

This independent nonprofit provides extensive information on vaccine science and includes research on the effectiveness of specific vaccines.

Vaccines.gov

This U.S. Department of Health and Human Services site educates the public on various vaccine-preventable illnesses, including influenza. The flu section of the site includes basic information about the flu vaccine and a search tool to help you find places to get vaccinated in your area.

Best Information for Colds

Mayo Clinic

This website offers information that will help you determine whether your symptoms are related to a cold and when you need to see a doctor, and offers preventive tips that may help you avoid getting sick.

National Library of Medicine

The common cold section of the MedlinePlus website provides comprehensive information on the causes and symptoms of the common cold, as well as links to information on how to determine whether you are suffering from a cold, the flu, or an allergy. It also includes information on potential treatments and therapies.

Best Resources for Parents

Healthy Children

This American Academy of Pediatrics site focuses on how to identify flu symptoms in your children, the potential treatments, and preventive tips.

KidsHealth — Flu

This website’s flu section offers basic educational and preventive information on keeping your family healthy and how to treat a child’s flu symptoms.

KidsHealth — Colds

The KidsHealth site also has a page dedicated to providing general information on common cold treatments for kids and potential complications.

Best Apps for Combating the Flu

FluView

The CDC’s FluView app allows you to track flu activity by region, which can also be helpful if you plan on traveling.

Zocdoc

Type in your location, your reason for seeing a doctor, and your insurance carrier and Zocdoc will help you book a doctor’s appointment in your area.

Find more apps to help you fight the flu in our article, 7 Apps to Help You Fight the Flu.

Editorial Sources and Fact-Checking

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Flu Symptoms and Complications. Centers for Disease Control and Prevention. September 21, 2021.
Cold Versus Flu. Centers for Disease Control and Prevention. September 16, 2021.
Fashner J, Ericson K, Werner S. Treatment of the Common Cold in Children and Adults. American Family Physician. July 15, 2012.
People at Higher Risk of Flu Complications. Centers for Disease Control and Prevention. October 12, 2021.
Flu Season. Centers for Disease Control and Prevention. September 28, 2021.
Common Colds: Protect Yourself and Others. Centers for Disease Control and Prevention. October 7, 2020.
How (Not) to Catch a Cold. Houston Methodist On Health. December 21, 2020.
Facts About the Common Cold. American Lung Association. October 23, 2020.
Breathe Easier — Quit Smoking. Centers for Disease Control and Prevention. September 30, 2021.
Types of Influenza Viruses. Centers for Disease Control and Prevention. November 18, 2019.
Past Pandemics. Centers for Disease Control and Prevention. August 10, 2018.
Liu R, Sheng Z, Huang C, et al. Influenza D Virus. Current Opinion in Virology. October 2020.
Rapid Influenza Diagnostic Tests. Centers for Disease Control and Prevention. October 25, 2016.
Key Facts About Influenza (Flu). Centers for Disease Control and Prevention. August 26, 2021.
Common Cold: Diagnosis and Treatment. Mayo Clinic. June 11, 2021.
What You Should Know About Flu Antiviral Drugs. Centers for Disease Control and Prevention. August 31, 2021.
Who Should and Who Should Not Get a Flu Vaccine. Centers for Disease Control and Prevention. August 24, 2021.
Colds in Children. Pediatrics and Child Health. October 2005.
Similarities and Differences Between Flu and COVID-19. Centers for Disease Control and Prevention. June 7, 2021.