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Colds and the flu are very common seasonal infections. They can have similar symptoms, but there are key differences.
The main difference between a cold and the flu is that the flu generally has more severe symptoms and possible complications.
According to the Centers for Disease Control and Prevention (CDC), more than 35.5 million people caught the flu during the 2018–2019 flu season, resulting in close to 34,000 deaths.
This article looks at the differences between a cold and the flu, along with ways to treat the symptoms and prevent these seasonal infections.
There are several key differences between these two illnesses.
Influenza viruses are responsible for the flu, with three main types affecting humans: influenza A, B, and C. The most common types during flu season are A and B.
As the common cold and the flu have similar symptoms, it can be tricky or even impossible to know which of these illnesses a person has.
In general, the flu is worse than a cold. While the symptoms of a cold come on gradually, flu symptoms begin abruptly, and they tend to be more intense.
A runny or stuffy nose is more common with a cold. On the other hand, the following symptoms are common with the flu but uncommon with a cold:
- fever — a temperature of 100°F (37.8°C or higher) — that lasts 3–4 days
- muscle aches, particularly in the lower back
- fatigue or weakness
- a headache
Neither vomiting nor diarrhea is usually associated with the common cold, but both can be present in the flu.
People may have the flu without key symptoms such as fever. To know for sure whether they have a cold or the flu, a person can get a special diagnostic test within a few days of their symptoms starting.
The symptoms of a cold or the flu are also similar to those of other respiratory illnesses, including COVID-19, which the SARS-CoV-2 virus causes.
Colds do not usually lead to any further issues, although they can increase the chance of people with asthma having an asthma attack. Conversely, the flu can lead to severe complications, such as pneumonia or bacterial infections. Each year, flu-related complications cause thousands of hospitalizations and deaths.
People can catch colds and flu in the same way. Both viruses are contagious and can transfer to a person who:
- has close contact with someone who has the virus
- breathes in respiratory droplets that contain the virus
- touches a contaminated surface
Colds are very common respiratory illnesses that are usually due to infections with rhinoviruses.
Colds are one of the most frequent reasons for people missing work or school, with the average adult in the U.S. having more than one each year. Most people will have had many colds from infancy all the way through to later life.
Viruses that cause the cold typically enter the body through the nose and sinuses. In response, the nose creates clear mucus to wash the virus away.
The symptoms of colds appear gradually and peak within 2–3 days. The most common symptoms include:
- a stuffy or runny nose
- sore throat
- mucus dripping down the throat
- watery eyes
There is no cure, but colds will get better on their own. People can manage the symptoms by resting as much as possible, drinking plenty of fluids, and using over-the-counter (OTC) cold medicines if necessary.
Complications are rare, and there is normally no need to visit a doctor. However, people with a weakened immune system and those with asthma or another condition that affects the airways could become seriously ill from a cold.
The flu is a common respiratory illness resulting from an infection with an influenza virus.
The flu is less common than colds, but when it does arise, it is more severe and can have serious complications.
One of the key symptoms of flu is feeling feverish or having a temperature of 100°F or above. However, not everyone with the flu will have a fever.
Common symptoms of the flu include:
- fever or feeling feverish
- a cough
- sore throat
- muscle or body aches
- runny or stuffy nose, though this is more common with a cold
- vomiting or diarrhea, especially in children
It is possible to prevent the flu to a certain extent. The seasonal flu shot protects to a significant degree against complications due to influenza A and influenza B, which are the types that usually cause seasonal epidemics.
Antibiotics do not work against either colds or the flu. Most people who have a cold or the flu will recover within 2 weeks without medical treatment. During this time, they can relieve their symptoms using home remedies.
If a person is at risk for severe flu complications, the CDC recommend prompt treatment with antiviral medications. These drugs can reduce symptoms, shorten the illness by 1–2 days, and prevent serious complications.
OTC drugs can relieve uncomfortable symptoms, including pains, aches, and fever, helping the person feel more comfortable while they recover. Drinking plenty of fluids and getting lots of rest can also speed up recovery.
The following home remedies can also help:
- saline nose drops can help clear a blocked nose
- vapor rubs can make it easier to breathe
- a vapor bath with eucalyptus can ease congestion
- gargling with salt water or sucking on a lozenge can ease the pain of a sore throat
- acetaminophen (Tylenol) and similar medications can relieve aches and pains
People should seek medical help if they notice any emergency warning signs.
Warning signs in children include:
- fast breathing or difficulty breathing
- bluish lips or face
- chest pain
- dull reactions
- fever above 104°F
Warning signs in adults include:
- shortness of breath or difficulty breathing
- bluish skin color
- persistent chest or abdomen pain or pressure
- dizziness or confusion
- a lack of urination
- severe muscle pain or weakness
- fever or cough that improves then worsens
The CDC provide a full list of warning signs.
The best way to protect against the flu is by having an annual vaccination, as this helps the body build immunity against influenza viruses so that it can fight them off more easily.
The CDC recommend that everyone over the age of 6 months get a flu shot every year, with rare exceptions.
The flu shot has a good safety and effectiveness record. Learn more here.
People can take steps to avoid catching viruses that cause respiratory illnesses and to reduce the risk of them spreading. These steps include:
- avoiding close contact with others when either person is sick
- covering the mouth and nose when sneezing or coughing
- washing the hands regularly and using an alcohol-based hand rub when this is not possible
- avoiding touching the eyes, nose, or mouth
- disinfecting surfaces regularly, especially when someone is ill
- getting plenty of sleep, staying active, and reducing stress, if possible
- drinking plenty of fluids and eating nutritious foods
Due to the COVID-19 pandemic, reducing the spread of respiratory illnesses, including the flu, during flu season is more important than ever.
Shop for flu remedies
People can find a wide range of cold and flu remedies in drugstores, supermarkets, and online.
The common cold and the flu are seasonal respiratory illnesses that occur as a result of different viruses. The main difference is that the flu can have more severe symptoms and is more likely to cause serious complications and hospitalization.
In most cases, the symptoms of both a cold and the flu are relatively mild, and people can usually manage them at home. However, it is important to look out for warning signs, especially in people with a higher risk for complications.