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

Influenza, or the flu, can be tricky to tell apart from the common cold. 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 the 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.

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 Mount Sinai South Nassau 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 an article in American Family Physician, 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

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 the 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 groups of people are more susceptible to complications from 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 a 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 your risk of catching a cold or the flu, according to the CDC. As does the use of immunosuppressive medications such as steroids, biologics, chemotherapy, or transplant medications.

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.

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 the 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, according to the CDC.

A novel strain of H1N1 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, notes the CDC.

Influenza B

Less common than influenza A, these viruses cause similar symptoms and can lead to seasonal outbreaks. Per the CDC, 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 not thought to cause epidemics. Seasonal flu vaccines, which contain strains of influenza A and B, do not protect against influenza C viruses, cautions the CDC.

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 Current Opinion in Virology notes that it could eventually pose more of a threat to humans.

PCR-based tests can be done to look for common colds, but they’re not generally available to the public for routine use; they’re usually reserved for hospital patients with pneumonia or a severe respiratory tract infection. If your symptoms are more severe, your doctor may order tests or X-rays to rule out certain illnesses, such as strep throat or pneumonia.

To diagnose the flu, doctors sometimes use a rapid influenza diagnostic test, notes the CDC. Swab samples from the nose or back of the throat are tested for influenza viral antigens (substances that cause your immune system to form antibodies). Test results are usually ready in less than 15 minutes but are not always accurate. Other more reliable flu tests can be performed only in hospitals or specialized laboratories.

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, older adults, 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 the Flu Last?

There is no cure for either the flu or the common cold. Over-the-counter options can ease throat pain and cough, decongest the nose and sinuses, and lessen body aches and headaches.

Cold medicines and pain relievers can have side effects and pose health risks, especially for people who have preexisting conditions such as high blood pressure. The Mayo Clinic cautions that children and teenagers with flu-like symptoms should never take aspirin for pain or fever, because it has been linked to the potentially life-threatening condition Reye's syndrome.

Prescription antiviral drugs can be used to treat the flu, especially in patients at higher risk of complications (such as those with asthma, diabetes, or heart disease). According to the CDC, when taken within two days of the appearance of flu symptoms, these drugs can shorten the time you are sick, may reduce complications, and may lessen the severity of symptoms.

The U.S. Food and Drug Administration has approved four antiviral drugs: oseltamivir (Tamiflu), peramivir (Rapivab), zanamivir (Relenza), and baloxavir marboxil (Xofluza).

RELATED: 8 Ways to Keep the Flu From Spreading Through Your Household

Prevention of Colds and the Flu

To avoid getting the flu in the first place, the CDC recommends that everyone six months and older get a flu vaccine every year (unless you’ve had a severe allergic reaction in the past). These vaccines protect against the viruses that public health officials anticipate will be most common during the upcoming flu season.

There is no vaccine to prevent the common cold, but practicing good hygiene can reduce the risk of illness or spreading viruses to others. "Most colds stem from viruses that are spread from person to person through close contact," says William Schaffner, MD, a professor of preventive medicine at Vanderbilt University School of Medicine in Nashville, Tennessee. The CDC recommends washing your hands often for at least 20 seconds at a time and not touching your eyes, nose, or mouth with unwashed hands. Use alcohol-based hand sanitizer if soap and water aren’t available.

Wearing a mask can help decrease the transmission of common colds and the flu; masking, along with other precautions taken during the pandemic, is thought to be responsible for the large drop in flu cases during 2020 and 2021, notes the CDC. If you have a cold or the flu symptoms, mask up if you’ll need to be around other people.

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 doctor 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, says the CDC, severe flu complications can include heart infections such as myocarditis, and brain inflammation illnesses such as encephalitis.

Learn More About Complications of Colds and the 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, according to a report in the journal Paediatrics & Child Health.

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

COVID-19, the disease caused by the coronavirus SARS-CoV-2, and the flu are both contagious respiratory illnesses and share many symptoms, including fever or feeling feverish, chills, cough, difficulty breathing, fatigue, sore throat, runny or stuffy nose, body aches, and headache. You might even wonder, based on your symptoms, whether a severe cold is COVID-19.

Two differences: COVID-19 symptoms can take longer than flu symptoms before they appear after infection, and people can be contagious for longer.

According to the CDC, based on available information, COVID-19 spreads more easily than the flu.

COVID-19 and the flu are caused by different viruses. One doesn't cause the other, though it is possible to contract both at the same time. Diagnostic testing can confirm which virus you're dealing with, notes the CDC.

COVID-19 vaccines are now approved and recommended by the CDC for anyone 6 months and older.

RELATED: Is It a Cold, the Flu, or COVID-19?

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. According to the Mayo Clinic, these include:

• Asthma
• Bronchitis
• Pneumonia
• Ear infections
• Sinus infections
• Strep throat

Favorite Organizations for Essential Information

American College of Obstetricians and Gynecologists

The college'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

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

Founded in 1973, this nonprofit is dedicated to educating the public and healthcare providers about infectious diseases. Its influenza webpage 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

The organization'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

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.