Cold vs. Flu: Similarities and Differences

A cold and the flu differ in their causes, severity, and potential complications.

Different Viruses Cause Them

More than 200 viruses can lead to a cold, with rhinovirus being the most common. Other cold-causing viruses include coronavirus (the common cold strain), parainfluenza, human metapneumovirus, and adenovirus.

The influenza virus, primarily types A and B, including strains like H1N1, causes the flu.

The Flu Is More Severe

One of the most notable differences between the cold and the flu is the timing and severity of symptoms. Colds develop gradually and cause mild discomfort, making you feel unwell but not severely ill. In contrast, flu symptoms usually appear suddenly and are much more intense.

Cold symptoms typically peak on the second or third day and resolve within 5-7 days. The flu lasts 1-2 weeks, but the fatigue can linger for several weeks.

The Flu Has a Higher Risk of Causing Complications

Colds rarely lead to complications, though they can occasionally trigger asthma attacks or cause ear or sinus infections. While most people recover from the flu without serious issues, it can lead to more dangerous health problems, some of which can be life-threatening.

Flu complications might involve:

• Bronchitis—swelling and mucus buildup in the airways
• Pneumonia, a lung infection
• Sepsis, a life-threatening response to infection
• Swelling of the brain, heart, or muscles 

Despite their differences, colds and the flu share similarities in who they affect, how the viruses spread, and how to prevent the illnesses.

They Primarily Affect the Same Groups

Colds and the flu can affect anyone, but certain groups are more likely to get sick or have a more challenging time recovering from either illness.

People at higher risk for getting sick or having a more severe illness include:

• Adults 65 years or older
• People who are pregnant
• People with chronic health conditions like asthma or heart disease
• People with a weakened immune system
• Children under 5 (and especially those under 2)

They Spread the Same Way

Both colds and the flu spread through respiratory droplets when someone coughs, sneezes, or talks. You can also get infected by touching surfaces contaminated with the virus (e.g., phones, doorknobs, light switches) before touching your mouth, nose, or eyes. 

Viruses that cause colds and the flu tend to survive longer and spread more efficiently in cool, dry conditions. This is why both conditions are more common in the fall and winter when temperatures drop and humidity levels are lower.

The Prevention Strategies Are Similar

The following tips can help reduce your chances of getting or spreading the flu or a cold:

• Avoid close contact (like kissing or sharing cups) with others when sick
• Avoid crowded places, especially if you’re in a high-risk group
• Avoid touching your eyes, face, nose, or mouth with unwashed hands
• Clean and disinfect surfaces you touch often
• Cover your mouth and nose when coughing or sneezing
• Stay away from people who are sick
• Stay home when you’re sick
• Wash your hands often with soap and water for at least 20 seconds

Healthy lifestyle choices can also help prevent the cold and flu. Maintaining a healthy lifestyle involves getting enough sleep, drinking lots of water, eating a balanced diet, avoiding smoking, and staying active. These steps can strengthen your lungs and immune system, helping you fight colds and the flu.

Some people also take supplements like elderberry, vitamin C, vitamin D, or zinc to boost their immunity and help prevent illness.

While the cold and flu share many preventative measures, only the flu has a vaccine for treatment and prevention. There’s no vaccine for the common cold because various viruses cause it. An annual flu vaccine can help protect you against the most common flu strains, like influenza A and B.

Since different viruses cause colds and the flu, it is possible to catch both. However, a co-infection is rare because viruses like influenza and rhinovirus compete—with one virus typically growing faster in the body.

You might not realize if you contract a cold and the flu simultaneously, but you’ll likely feel worse than you would with just one infection.

A cold resolves in about a week, and the flu typically resolves within a couple of weeks with rest, hydration, home remedies, and over-the-counter (OTC) medications. You should notify your healthcare provider if you or a loved one experiences a cough that worsens while other symptoms improve, a fever that lasts more than three days, dehydration, or worsening chronic conditions.

In more severe flu cases, your primary care provider may refer you to a specialist, such as a pulmonologist for lung-related issues or an infectious disease specialist for flu complications.

Go to an urgent care clinic if you or someone you know experiences:

• Breathing that feels a bit more difficult
• Persistent vomiting or diarrhea that doesn’t improve
• Moderate dehydration (a sign of which might be producing no urine for eight hours)
• Persistent high fever that doesn’t respond to medicine of over 102 degrees Fahrenheit (38.9 degrees Celcius) in children or 103 degrees Fahrenheit (39.4 degrees Celcius) in adults
• Symptoms that worsen after initially improving

Seek emergency care if you or someone you know experiences:

• Bluish or gray lips or face
• Chest pain 
• Confusion
• Fainting
• Retractions (ribs pulling in with each breath in young kids)
• Seizures 
• Severe dehydration (dizziness, hallucinations, no urine output)
• Severe weakness 
• Shortness of breath
• Temperature above 104 degrees Fahrenheit (40.0 degrees Celcius)

Colds and the flu are common respiratory illnesses, but different viruses cause them. Both share symptoms like runny nose, congestion, cough, and sore throat. However, flu symptoms tend to be more sudden and severe and also cause fever and body aches.

Prevention strategies include practicing good hygiene, avoiding sick people, and cleaning frequently touched surfaces. While there is a vaccine for the flu, there is no vaccine for the common cold. Knowing the differences between the two illnesses can help you manage your symptoms and seek medical care when necessary.