How Does the Body React Differently to Cold and Flu Viruses?

01/24/2026

What is the common cold?

A common cold, or cold, is a contagious upper respiratory infection that primarily affects your throat, nose, windpipe, and sinuses. There are more than 200 viruses that can result in a common cold, and among them, rhinoviruses are the most common. Colds are referred to as common because they are widespread and affect you more than any other illness. In your life, you will have more colds than any other condition. On average, adults catch 2 to 3 colds a year, and children may catch 4 or more. Symptoms of the common cold occur in three stages: early, active, and late.

Symptoms of the common cold:

The common cold usually progresses through three stages: early, active, and late.

Stage 1:

Stage 1, also known as the early stage, begins on the day you catch the cold and may last up to 3 days. Within 1 to 3 days, you may experience a tickle in your throat. The first symptom that most people notice is a tickly or sore throat.  In addition to this, you may also experience other signs such as a runny nose, hoarseness, cough, and a stuffy nose.

Stage 2:

Stage 2, commonly known as the active stage, refers to days 4 to 7, when symptoms usually worsen. You may experience the following symptoms in addition to the symptoms of stage 1:

• Body aches

• Fatigue

• Fever (common in children)

• Runny eyes and nose

• Headache

Stage 3:

Stage 3, known as the late stage, covers days 8 to 10. In this stage, symptoms usually start to resolve, making you feel better and at ease. However, a few symptoms may persist for a while but will resolve over time. After a respiratory infection, many people can develop a nagging cough that may last up to 2 months.

If you experience new complications or a return of cold symptoms, consult a doctor. You have probably developed a new infection.

What is the flu or influenza?

The flu is an infectious illness caused by influenza viruses. It causes a vast range of symptoms, ranging from body aches to respiratory symptoms that are usually serious. This condition is more common in winter than any other season, affecting a myriad of masses at once. The highest number of flu cases occurs between December and February in the US. It affects 20 to 40 million people every year in the US, standing out as one of the common infectious diseases. The flu and the common cold usually share comparable symptoms, such as a runny nose and cough. However, the common cold’s symptoms are mild while the flu’s symptoms can be severe, increasing the chance of further complications.

Symptoms of the flu:

Unlike the common cold, flu symptoms develop quickly and range from mild to severe. The following are the common symptoms of the flu:

• Fever

• Chills

• Headache

• Sore throat

• Body aches

• Runny or stuffy nose

• Tiredness

• Diarrhea or vomiting (common in kids)

You won’t experience all of the aforementioned symptoms. The symptoms can differ from one patient to another depending on the influenza virus. The most common influenza viruses are influenza A, B, and C.  Among them, influenza C causes mild symptoms and is not seasonal, while influenza A and B usually cause severe symptoms and are seasonal.

Does the body react differently to both of them?

Yes, the body reacts differently to the common cold and flu in many ways, including the speed of onset, the intensity of the immune response, and the areas of the respiratory system affected. The difference is mainly because influenza results in a more systemic and aggressive inflammatory response, while colds usually cause more localized inflammation in the nasal passages.  Let’s dig into how the body reacts differently to both viral respiratory infections:

Onset and progression:

As mentioned above, the symptoms of a cold usually develop slowly over a period of 1 to 3 days, with a sore throat as the first symptom. On the other hand, symptoms linked to the flu strike suddenly, typically within a few hours.

Immune response intensity (fever and aches):

In flu cases, the immune system causes an intense and rapid response, resulting in a high fever that may last 3 to 4 days. In addition to the high fevers, it may also cause body aches, headaches, and extreme fatigue. On the other hand, fever is rare in adults with a common cold, but common in children. Body aches and fatigue are usually absent or very mild in nature.

Respiratory impact:

In common colds, the immune response is typically focused on the upper respiratory tract, causing symptoms such as a sore throat, a stuffy or runny nose, and sneezing. On the other hand, the flu affects the whole body and mainly causes a severe, dry, and nagging cough.

Duration and complications:

The common cold typically lasts for 7 to 10 days, with no serious symptoms, and is manageable at home. On the other hand, the flu can last 1 to 2 weeks, with fatigue continuing for several weeks. Additionally, it also increases your risk of other complications, for instance, sinus infections, bronchitis, and pneumonia.

Are the common cold and the flu contagious?

Yes, both are highly contagious and can easily spread from one person to another. You may end up catching a cold if you come into contact with a surface or breathe moist air that contains the common cold virus. An infected person can release droplets of fluid containing the cold virus into the air while sneezing and coughing. If you breathe in those droplets or touch them, the virus can get into you and make you ill. You and other infected people can spread the virus to other people if precautions are not exercised.

The flu is also contagious, as mentioned above. According to reports, every infected person spreads this illness to 2 or more people. You may develop symptoms 2 to 4 days after exposure to the virus. This illness can spread directly or indirectly through contact with the infected person. Some of the common ways of catching the flu:

• Sitting close or next to someone who is infected.

• Touching the surface that may be contaminated.

• Touching the hands or face of the infected person.

The takeaway:

The common cold and the flu are common conditions that affect millions of people worldwide every year, with symptoms ranging from mild to intense. The common cold can affect anyone who comes into close contact with an infected person or touches a contaminated surface, with symptoms lasting 7 to 10 days and are localized. On the other hand, the flu is an infectious disease that is caused by influenza viruses, with the highest cases reported in the winter season. The body reacts differently to both conditions primarily because of the speed of onset, the intensity of the immune response, and the area of the respiratory system affected. If symptoms of any condition worsen, kindly let your doctor know about it to prevent further complications. If we compare colds vs flu, flu symptoms are more severe.