Cold vs. flu: What’s the difference?

Cold vs. flu causes | Prevalence | Symptoms | Diagnosis | Treatments | Risk factors | Prevention | When to see a doctor | FAQs | Resources

You open your eyes one morning; your throat is scratchy, your head hurts, and although you just woke up, you feel tired. All you want to do is pull the covers up over your head and go back to sleep. You know that if it’s a cold, you will probably feel better in a few days, but if it is the flu, you should call your doctor—after all, medicines for the flu work best if you take it within a day or two of symptoms. But right now, you aren’t sure what to do because your symptoms fit both.

The common cold and influenza (the flu) are both respiratory illnesses. Although it can sometimes be difficult to tell them apart, generally, the flu is more serious. In this article, we explain the symptoms of cold versus flu, what causes these viral infections, and when to see a doctor. 

Causes

Cold

There are more than 200 different viruses that cause the common cold; rhinoviruses cause 50%. Some other viruses that cause colds include respiratory syncytial virus, human parainfluenza virus, adenovirus, and human metapneumovirus.

Some colds are caused by types of coronaviruses (such as 229E, NL63, OC43 andHKU1), according to the Centers for Disease Control and Prevention (CDC), the same type of virus that causes COVID-19. But COVID-19 is different from these coronaviruses in that it generally causes more severe illness, and is entirely new. Symptoms of COVID-19 include fever, chills, shaking, loss of taste or smell, shortness of breath, and diarrhea. 

Colds are easily spread to others through airborne droplets from a cough or sneeze by an infected person. These droplets can remain in the air even after you have left the area. When someone inhales them, they can catch your cold. If the droplets land on a surface, they can survive on the surface and remain infectious for several hours. Touching that surface and then touching your face can transfer the virus to you. That’s why it is essential to wash your hands frequently. 

Many people think colds are caused by being in cold weather, but they are not. Colds occur more frequently in the fall and winter. One reason the virus spreads more quickly in the colder months is because people spend more time indoors and in closer proximity to one another. 

Flu

While there are several hundred viruses that cause colds, there is only one that causes flu: influenza. Influenza is further categorized into four different types: A, B, C, and D. Influenza viruses A and B cause seasonal epidemics, and type A is the only one known to cause pandemics. Type C causes only mild symptoms, and type D is primarily found in cattle. 

As with the cold, the flu virus is passed from person to person through inhaling droplets in the air or touching a surface that someone with influenza recently contaminated. The flu can spread starting the day before symptoms appear and for up to seven days after the start of symptoms.

RELATED: How long is the flu contagious?

Prevalence

Cold

The cold virus is often referred to as the “common cold” because, well, it is common. There are more than 1 billion cases of a cold in the United States each year. It accounts for more doctor’s visits than any other health problem and is the most frequent reason for missing school or work.

Adults get an average of two to four colds per year, and children get an average of six to eight colds per year, according to the American Lung Association.

Flu

Because influenza is not a reportable disease, the CDC can only estimate how many people in the United States are affected each year. They develop estimates based on data from the U.S. Influenza Surveillance System—a collaborative effort between federal, state, and local health departments. 

Flu season, which is from October until May, is when most people develop the flu. During the season from October 2019 through April 2020, the CDC estimates:

• 39 to 56 million cases of influenza.
• 18 to 26 million doctor’s visits were the result of the flu.
• 410,000 to 740,000 people with the flu required hospitalization.
• 24,000 to 62,000 people died as a result of the flu or from complications. 

* Based on a study completed in 2015 by lead researcher Dr. Steven Riley

Symptoms

Cold

Common cold symptoms generally start one to three days after exposure to the virus and usually last seven to 10 days. You might feel sluggish, but the cold is relatively harmless and usually clears up without medical intervention. Over-the-counter medications help manage symptoms, which include:

• Stuffy or runny nose (thick yellow or green discharge) 
• Scratchy or sore throat
• Sneezing
• Watery eyes
• Low-grade fever
• Mild hacking (dry) cough
• Achy muscles
• Headache
• Mild fatigue
• Chills

Colds (a respiratory tract infection) can sometimes lead to a secondary infection, such as an ear infection or sinus infection. 

Flu

Flu symptoms are often more severe than those of a cold and can last one to two weeks. Symptoms include:

• Fever, feeling feverish, or chills 
• Cough
• Sore throat
• Runny or stuffy nose
• Muscle aches
• Body aches
• Headaches
• Fatigue

Some people might have vomiting or diarrhea, but this is more common in children.

The flu can also lead to moderate complications such as sinus or ear infections. Pneumonia is also a complication of the flu, which can be life-threatening. People with underlying health conditions may be more susceptible to complications from the flu. 

Diagnosis

Cold

Colds are diagnosed based on your symptoms. Because other conditions, such as bacterial infections, allergies, flu, can have similar symptoms, it is sometimes diagnosed by eliminating other conditions. There are specialized tests which can identify a handful of the common viruses causing the common cold, but these are generally reserved for very sick patients.

Flu

Influenza can also be diagnosed based on symptoms; however, there are laboratory tests to tell if you have the flu. This test is more accurate when taken within the first few days of symptoms. Therefore, if you think you have the flu, you should immediately contact your doctor. 

Treatments

Cold

There isn’t a cure for the common cold; however, over-the-counter medications reduce cold symptoms. These include:

• Decongestants (Sudafed, Advil Multi-Symptom Cold & Flu, Mucinex, Sinex)
• Antihistamines (Dimetane, Chlor-Trimeton, Tavist)
• Cough medicine (Delsym, Robitussin, Mucinex)
• Pain relievers (Tylenol, Advil, Aleve)

Also, you should rest and increase fluid intake. You might also find it helpful to gargle with salt water, use petroleum jelly for raw or chapped skin, and use warm steam to lessen congestion. 

Antibiotics do not work because viruses, not bacterial infections, cause colds. 

Precautions while treating a cold:

• You should never give aspirin to a child with a fever, as it is associated with Reye’s syndrome, which can be a serious or deadly disorder. 
• While a cold is not usually dangerous to pregnant women, some over-the-counter medications could be harmful during pregnancy. You should talk to your doctor if you have a fever, as fevers during early pregnancy could cause congenital disabilities, according to the Cleveland Clinic. 

Flu

If you have the flu, it is advisable to stay home, get plenty of rest, increase your fluids, and take over-the-counter medications to relieve discomfort. There are also four antiviral drugs recommended by the CDC and approved by the FDA for the treatment of influenza: Tamiflu, Rapivab, Relenza, and Xofluza. Xofluza is also now approved to prevent the flu after exposure to the virus.

You should discuss any present medical conditions with your doctor before taking these medications. Relenza is not recommended for people with lung diseases, and Xofluza is not recommended for pregnant women or those who are breastfeeding.

RELATED: Does the flu shot or Tamiflu prevent COVID-19?

Risk factors

Cold

Everyone is at risk of getting a cold. Children tend to get colds more often because their immune systems are immature, meaning their exposure to viruses is limited. Because they spend time close to other children in daycare or school, they are more likely to be exposed to cold viruses. As their immune system learns to recognize cold viruses, it starts to attack similar viruses, which is why the number of colds lessens as you get older, according to John Hopkins Medicine.

Colds are more common during the fall and winter months because people spend more time indoors where cold viruses can linger in the air and on surfaces. The atmosphere is also drier during these months, and the lack of humidity can dry out nasal passages, making them more susceptible to cold viruses, according to John Hopkins Medicine.

Flu

Everyone is also at risk of getting the flu. Some diseases may increase the risk of developing serious flu complications. These include: 

• Chronic lung diseases such as asthma, COPD, bronchiectasis, cystic fibrosis
• Heart disease
• Chronic kidney disease
• Diabetes
• Morbid obesity
• Anemia
• Immune disorders, such as HIV/AIDs
• Current treatments that suppress the immune system
• Liver disorders
• Children and adolescents receiving long-term aspirin therapy

Prevention

Cold 

There isn’t a vaccination that will prevent you from getting a cold or a cure if you get it, but there are steps you can take to reduce your risk:

• Thoroughly wash your hands using soap and water frequently. After applying soap, rub your hands vigorously for 20 seconds under warm water. 
• If soap and water are not available, use an alcohol-based hand sanitizer.
• Avoid close contact with people who have a cold. 
• Try not to touch your face, especially your nose and eyes, when you are around people who have a cold until you thoroughly wash your hands.

The best way to prevent spreading a cold to other people is to stay home if you are sick. If you must go out, avoid close contact with other people and refrain from hugging, kissing, or shaking hands. Actively work to reduce sharing cold germs with others by coughing or sneezing into facial tissue, and then promptly disposing of the tissue. After coughing or sneezing, thoroughly wash your hands to avoid touching objects and leaving germs behind. Rhinoviruses can survive up to three hours on surfaces, according to John Hopkins Medicine. Use disinfectants that kill viruses to clean surfaces. 

Flu

The best way to prevent getting influenza is to get a yearly flu vaccine. The effectiveness of the vaccine varies from year to year based, in part, on how well matched it is to the current flu that is circulating. However, it generally reduces your chance of getting the flu by 40% to 60%, according to the CDC. Even though it does not eliminate the possibility of getting the flu, it prevents millions of flu cases each year. Getting the flu vaccine can also reduce the severity of the flu if you do get it. 

Personal care, including washing hands often and avoiding close contact with others who are sick, can also reduce your risk of getting the flu. 

When to see a doctor

Cold

Most of the time, you don’t need medical care for a cold. Over-the-counter medicines can reduce symptoms and make you more comfortable. However, there are times when you should see your healthcare provider for a cold:

• If your symptoms don’t go away within 10 days.
• If you develop new symptoms.
• If a child under three months of age has a cold.

Flu

The best time to see your doctor for the flu is to get your annual flu shot before you get it. If you do get the flu, you should contact your doctor within the first day or two. There are antiviral medications that can help reduce the intensity and duration of symptoms, but they work best if taken within the first few days. 

You should also contact your medical provider if:

• You have trouble breathing, experience chest pain, or are coughing up yellow, green, or bloody phlegm, according to the American Lung Association.
• Your cough doesn’t go away or is preventing you from sleeping.
• You have a high risk of complications, such as young children under five years old, people over 65 years old, pregnant women, and people with certain medical conditions such as asthma, diabetes, and heart disease.

If you are experiencing severe symptoms, you should seek medical attention.

Severe symptoms in children include:

• High fever (above 104°F)
  • In children less than 12 weeks of age, any fever
• Fever that lasts for more than three days
• Trouble breathing, fast breathing, or wheezing
• Ribs pulling in with each breath
• Bluish skin color (lips, face)
• Chest pain
• Earache or ear drainage
• Difficulty waking up, not alert
• Dehydration
• Irritability
• Seizures
• Symptoms that improve and then return with a fever or worse cough
• Worsening of chronic medical conditions (such as diabetes or heart disease)
• Vomiting or stomach pain

Severe symptoms in adults include:

• A high, prolonged fever (above 102°F) with fatigue and body aches
• Symptoms that last longer than 10 days or get worse
• Trouble breathing or shortness of breath
• Chest pain or pressure
• Fainting or feeling like you are going to faint
• Confusion or disorientation
• Severe or persistent vomiting
• Severe sinus pain in your face or forehead
• Swollen glands in the neck or jaw
• Seizures 
• Worsening of chronic medical conditions (such as diabetes or heart disease)

Frequently asked questions about cold and flu

How can you tell the difference between a cold and the flu?

Because they share many of the same symptoms, it can be challenging to know the difference between these respiratory infections based on symptoms alone. First, there is a laboratory test to see if you have the flu, which is most accurate within a couple of days of symptoms first appearing. Cold symptoms are generally milder and more gradual, lasting seven to 10 days. Flu symptoms are more severe and sudden, lasting one to two weeks.

What are the symptoms of the flu versus the symptoms of a cold?

The main differences between the cold and flu are that you are more likely to have a fever and chills with flu and symptoms are more severe. Some potential differences:

• A fever and chills are common with the flu but not with a cold.
• Sneezing is expected with a cold but not usually associated with the flu.
• Runny and stuffy noses are more common in a cold than with the flu.
• Headaches are common with the flu but are not necessarily associated with a cold.

What is more dangerous: the coronavirus disease or seasonal influenza?

The severity of COVID-19 and influenza symptoms are both considered mild to severe, and similar groups are considered “high risk” for severe symptoms and/or complications with both illnesses. As of October 2020, the CDC reports more than 7.5 million coronavirus cases and 200,000 coronavirus-related deaths in 2020 whereas preliminary data estimates up to 56 million flu illnesses and up to 62,000 flu-related deaths for the 2019-2020 flu season.

Is it possible to have the flu and COVID-19 at the same time?

You can have both the flu and COVID-19 at the same time, according to the CDC. Many health experts worry that the U.S. will face two epidemics simultaneously, according to Scientific American Magazine, which could stretch our healthcare system more than it has been with COVID. It is possible that mitigation efforts, such as limiting time indoors with others outside your household members, wearing masks, social distancing, and increased handwashing, can lower the number of people who get the flu. 

Resources

• Common cold: Protect yourself and others, CDC
• Flu symptoms and complications, CDC
• Common cold, Cleveland Clinic
• Common human coronaviruses, CDC
• Cold and flu viruses: How long can they live outside the body? Mayo Clinic
• Common cold, MedlinePlus
• Facts about the common cold, American Lung Association
• Influenza surveillance system, CDC
• 2019-2020 U.S. flu season: Preliminary in-season burden estimates, CDC
• Estimating the life course of influenza A(H3N2) antibody responses from cross-sectional data, PLOS Biology
• Common cold, Johns Hopkins University
• COVID data tracker, CDC
• Coronavirus FAQs, CDC
• Coronavirus and the flu: A looming double threat, Scientific American