The common cold and the flu share many features: They’re both caused by viral infections, have similar symptoms, and usually can be treated at home. They also typically develop in stages, with certain symptoms emerging as the infection progresses. But there are differences in the onset, severity, and duration of the typical cold or bout of influenza.
How to Tell the Difference Between a Cold and the Flu
A cold and the flu are both respiratory infections, but they’re caused by different viruses. A cold can be caused by more than 200 distinct viruses, according to the Centers for Disease Control and Prevention (CDC), while there are only a handful of viruses that cause the flu. The flu is usually more intense than the common cold, says the CDC. (1)
Cold symptoms tend to develop gradually, while flu symptoms can come on suddenly, without warning. (2)
What Are the Stages of a Cold?
Cold symptoms can differ from person to person, but they generally appear about one to three days after exposure to a cold-causing virus. In most cases, cold symptoms will peak within two to three days. (1)
The signs that you have a cold usually develop slowly. The most common cold symptoms include fatigue, sore or scratchy throat, nasal congestion or stuffiness, and a runny nose, followed by sneezing and coughing. Fever is not typical with a cold, but a low-grade fever isn’t out of the question. (3)
The mucus discharged by a runny nose may change color over the course of the illness, starting out clear and becoming thicker, yellow, or green.?Postnasal drip, in which mucus accumulates or drips in the back of the throat, can further aggravate a sore throat or cough. (1)
Symptoms usually disappear in 4 to 10 days, although a cough often lasts into the second week. (3) A cold may last longer or be more severe in people who have chronic health issues. (1)
If your symptoms persist more than 10 days or keep coming back, then something else may be going on, such as?allergies,?sinusitis, or a secondary infection.
“Fever is an important sign,” says?Norman Edelman, MD, a professor of medicine at the State University of New York at Stony Brook. Adults with a fever of 102 degrees F or higher and children with a fever of 103 degrees F or higher should see a doctor.
The contagious period for the common cold has its own life span. A cold is most contagious during the first day or two after symptoms develop. (3).
RELATED: 7 Home Remedies to Stop a Bad Cough
What Are the Stages of the Flu?
Flu symptoms usually start within one to four days after infection. Unlike a common cold, the effects of an influenza virus infection can come on very suddenly. (2)
The first signs of the flu are often a fever or chills, accompanied by headache, sore throat, dry cough, runny nose, muscle aches, and fatigue. (2)
As the illness progresses, a person may have warm, flushed skin, watery or bloodshot eyes, a severe cough that produces phlegm, and nasal congestion. Nausea and vomiting may also occur, especially among children. (4)
A bout of the flu typically lasts for several days or occasionally weeks, with severe symptoms subsiding in two to three days. However, weakness, fatigue, dry cough, and a reduced ability to exercise can linger for six to eight weeks. (4)
How Long Is the Flu Contagious?
A survey conducted by the National Foundation for Infectious Diseases revealed that 41 percent of people think the flu is only contagious after symptoms start. (5) That’s not true.
An adult infected with?influenza may be contagious from one day before symptoms start until five to seven days after becoming sick. Children may continue to be contagious for longer than seven days, according to the CDC. (2)
Staying home until your contagious period has likely passed will help you avoid passing germs on to other people.
Other simple steps can keep you from spreading infection to others or picking up a virus from other people around you at school, work, or at home. Covering your mouth and nose when coughing or sneezing, using tissues to contain respiratory secretions, and in certain cases wearing a mask are also effective, according to the CDC.
“It’s really basic public health practices,” says?Catherine Troisi, PhD, an associate professor at the University of Texas School of Public Health in Houston. “You should wash your hands, stay home if you’re sick, get enough sleep, and eat well.”
What if a Cold or the Flu Won’t Go Away?
When?complications?develop, a person will likely be sick for longer than a week or two, depending on the severity of the complication, how quickly a person receives treatment for it, and how well the patient responds to treatment. Other factors that may affect recovery time include the presence of comorbidities like asthma, chronic obstructive pulmonary disease (COPD), certain cardiac conditions, and immunocompromising conditions like diabetes.
Signs of severe complications that should prompt you to seek medical attention include the following, according to the CDC (6):
- Difficulty breathing or shortness of breath
- Purple or blue discoloration of the lips
- Pain or pressure in the chest or abdomen
- High fever
- Sudden dizziness
- Severe or persistent vomiting
- Flu-like symptoms that improve but then return with fever and worse cough
Even in healthy people who don’t develop complications, the flu can cause symptoms that persist for weeks, including:
- Low appetite
- Dry cough
- Airway irritation that affects how long you can be active
- Loss of sense of smell, which in rare cases becomes permanent (6)
How Long Does Immunity Last?
With some viral illnesses, once you have been infected with it or have been vaccinated against it, you’re immune for life.
With the flu, however, immunity doesn’t last that long.
A 2017 study confirmed that immunity declines over the months following vaccination or infection. (7)
Getting vaccinated every year is important to lower your likelihood of getting the flu, not only because of waning immunity prior to flu virus exposure, but also because of ongoing viral mutations, according to the CDC. It takes about two weeks to develop immunity to the flu, and experts recommend getting vaccinated before flu season is in full swing to ensure adequate protection. (4)
“I think part of the problem with getting people vaccinated is people don’t understand how serious [the flu] can be,” says Dr. Troisi. “They confuse it with the common cold. But if you actually have the flu, you can get very sick.”
When Is Cold and Flu Season?
While it’s possible to get the flu year-round, most people get sick in the fall and winter. Flu season generally peaks between December and February, and can sometimes stretch into May. (8)
Most people get colds in the winter and spring, according to the CDC, but it’s possible to catch a cold in the summer or fall too. (1)
Can the Same Home Remedies and Medicine Be Used for Both Cold and Flu?
There is no cure for a cold, the CDC says — it will get better on its own. (1) But prescription antiviral drugs may help with the flu, especially when taken within two days of the onset of symptoms. People with health conditions such as asthma, diabetes, or heart disease that put them at high risk for flu complications should seek treatment right away. (9) While these medications usually only shorten the duration of the illness by about one day, the CDC notes that they may also reduce the probability of serious flu complications like pneumonia.
As for home remedies, there is evidence that zinc, taken by mouth in the form of lozenges, tablets, or syrups, can help reduce the length of colds if taken within 24 hours of the onset of symptoms, according to the National Center for Complementary and Integrative Health (NCCIH). The NCCIH adds that zinc can cause nausea and gastrointestinal issues, and that it can interact with other medication, such as antibiotics. (10)
There is no strong scientific evidence that any natural product can cure the flu, says the NCCIH. (10)
Over-the-counter options like acetaminophen (Tylenol) and nonsteroidal anti-inflammatory drugs like?ibuprofen (Advil) are effective treatments for fever and aches caused by either a cold or the flu. People with either illness should also be sure to rest and drink plenty of fluids. (3,4)
Additional reporting by Pamela Kaufman.
Editorial Sources and Fact-Checking
- Common Cold. Centers for Disease Control and Prevention. October 6, 2021.
- Key Facts About Influenza. Centers for Disease Control and Prevention. August 25, 2022.
- Common Cold. Merck Manual. September 2022.
- Influenza (Flu). Merck Manual. September 2022.
- Flu Behaviors and Treatments Survey National Results [PDF].?National Foundation for Infectious Diseases. November 26, 2013.
- Flu Symptoms and Complications. Centers for Disease Control and Prevention. August 25, 2022.
- Ferdinands?J, Fry A, Reynolds S, et al.?Intraseason?Waning of Influenza Vaccine Protection: Evidence From the U.S. Influenza Vaccine Effectiveness Network, 2011–2012 Through 2014–2015.?Clinical Infectious Diseases. March 1, 2017.
- Flu Season. Centers for Disease Control and Prevention. September 20, 2022.
- What You Should Know About Flu Antiviral Drugs. Centers for Disease Control and Prevention. September 7, 2022.
- 5 Tips: Natural Products for the Flu and Colds: What Does the Science Say? National Center for Complementary and Integrative Health. September 22, 2022.
- Interim Guidance for the Use of Masks to Control Seasonal Influenza Virus Transmission. Centers for Disease Control and Prevention. March 5, 2019.
- Influenza (Flu): Background and Epidemiology. Centers for Disease Control and Prevention. August 26, 2021.
- Flu Treatment. Centers for Disease Control and Prevention. October 15, 2021.