Flu and cold are distinct diseases, caused by different viruses, but share several common symptoms, which is why many people think both are synonyms. They are not. Although they are similar, influenza is the flu and the cold is cooled.

Let’s look at the similarities:

– Flu and cold are extremely common infections.
– Flu and cold are caused by viruses.
– Flu and cold can cause high respiratory symptoms such as coryza, cough and sneezing.
– Influenza and cold present similar form of contagion.
– Flu and cold are easily transmissible from one person to another.

There, the similarities stop there. Influenza is a stronger infection than the cold, usually lasts less and has a higher rate of complications, such as lung and heart problems. Flu can be dangerous in the elderly, infants and people with low immunity. The cold, on the other hand, rarely causes complications.

In this article we will stick only to the differences between cold and flu.

Influenza is a respiratory infection caused by viruses of the family Influenza. There are several subtypes of Influenza, which can cause more or less severe colds. The cold is also a viral respiratory infection, but there are dozens of different viruses that can cause the cold, such as Rhinovirus, Adenovirus, Parainfluenza, etc. Later on we will talk in detail about these viruses.

Two of the major differences between the flu and the cold are fever and the general condition of the patient. While the cold usually does not cause a fever (except in young children), in influenza the fever is common and is usually above 38 ° C, especially in children. In influenza, the patient is more prostrate, with a headache, and often with pain in the muscles and joints. In the cold, the patient has coryza, cough and sneezing, but is more or less well disposed, just bothered with these symptoms.

The table below summarizes the main differences and similarities between the flu and the cold:

Features Cold The flu
Type of virus Rhinovirus in most cases, but can also be caused by Adenovirus, Respiratory syncytial virus, Coronavirus, Parainfluenza, among others. They are caused by the Influenza virus family.
Fever Uncommon in adults, but common in young children. Usually low. Very common, usually above 38º.In children, the fever can pass from 40ºC.
Headache Rare. Very common.
Body aches Rare, when presents are light. Common and usually very uncomfortable.
Nasal coryza Very common. There may or may not be.
Sneezing Very common. There may or may not be.
Sore throat Very common and usually arises on the first day of illness. There may or may not be.
Weakness Uncommon. Very common and can last for several days.
Cough Mild to moderate dry cough. Common, there may be expectoration.
Incubation Time 24 to 72 hours. 24 to 96 hours.
Duration of illness 3 to 7 days in most cases, but in 1/4 of the patients, the disease persists for up to 14 days. 2 to 5 days, but coughing and tiredness may last for weeks to disappear.
Contagious period It begins 12 to 24 hours after the first contact with the virus, but the peak occurs between the 2nd and 4th days of symptoms. It begins 12 hours after the first contact with the virus, but the peak occurs between the 1st and 6th days of symptoms.
Opening of the board Gradual worsening over the first 2-3 days. Sudden onset, with peak of symptoms in a few hours.
Common complications Otitis media and sinusitis. Otitis media and pneumonia.

Based only on the clinical picture, we get an idea of ??what virus we are dealing with. For example:

  • Rhinovirus : is the main cause of common colds. It is a mild disease, which rarely causes fever in adults and usually lasts for 5 to 7 days. It can cause problems only in asthmatic patients by triggering exacerbations of the condition. There are more than 100 different rhinovirus serotypes.
  • Coronavirus – It also causes symptoms of cold, in addition to being able to cause diarrhea in some people, mainly in immunosuppressed patients. Asian pneumonia, which received much media attention in the early 2000s, is caused by a coronavirus serotype.
  • Parainfluenza – A cause of tracheobronchitis and pneumonia, it is usually more severe in young, immunocompromised children. In adults it causes a mild, cold-like picture.
  • Adenovirus – Usually causes a slightly richer picture, with fever, pharyngitis, hoarseness and conjunctivitis. It can be cause of pneumonia, diarrhea and viral meningitis. It is a virus that causes a slightly stronger cold.
  • Respiratory syncytial virus – Causes a more symptomatic picture, with sinusitis, otitis, conjunctivitis, cough. In the elderly, children and immunodeficients can cause pneumonia and lead to death. It is the most aggressive type of cold, but usually does not cause problems in adults or healthy older children.
  • Influenza – It is the agent that causes the flu. It causes a fairly symptomatic high respiratory infection. May be cause of viral pneumonia or facilitate the onset of bacterial pneumonia. Eventually, mutations in the virus lead to major epidemics, such as the Spanish flu in the early twentieth century, avian influenza and swine flu (influenza A subtype H1N1). Even so, in healthy adults, it does not cause major problems in most cases.

The clinical picture of viruses that affect the upper respiratory tract, be it influenza or cold, is very similar. Because these infections are usually self-limiting and do not require specific treatment, in most cases, it does not make sense to perform expensive tests and cause disruption to the patient only to know exactly which virus is responsible. In most people, the flu and the cold heal spontaneously without causing major problems.


The cold (called constipation in Portugal) is a mild infection of the airways. As already explained, it can be caused by several types of virus, with Rhinovirus being the most common. It is extremely contagious and transmission is through cough or sneeze sprays and by contact with infected hands.

Symptoms appear from 24h to 72h after virus transmission. It usually lasts 5 to 7 days, but in 25% of cases, the symptoms persist for up to 2 weeks. Most people have 3 to 5 colds a year.

The most common symptoms are rhinitis, cough and sneezing. Sore throat may occur in the first few days. Dry cough may last up to weeks after symptoms end. In adults, fever rarely occurs.

The cold is contagious for only the first 3 days of symptoms.

Complications are rare and include exacerbation of asthma and the presence of associated bacterial infection such as sinusitis


The flu is caused by the Influenza virus and has a healthier picture than the cold, with a high fever, body aches, headache, malaise, loss of appetite, sore throat and cough. In influenza, the symptoms usually appear suddenly unlike the cold, where they appear gradually. Cough and fever are early symptoms.

The mode of transmission is the same as that of the cold. The disease time can be up to 2 weeks, but usually lasts 4 to 7 days. The time the patient remains contagious lasts 1 to 2 days after the resolution of the fever.

Influenza also has a higher rate of complications, such as pneumonia from Influenza itself or from opportunistic bacteria , which take advantage of the patient’s weakened state to attack his or her lungs.

Both common and influenza A (H1N1) have similar clinical picture and complication rates, making it impossible to distinguish them without laboratory tests

In addition to the flu vaccine, there are already specific remedies against influenza, which when indicated, should be administered within the first 48 hours of illness. The best known is Tamiflu®. Specific treatment is indicated in children, the elderly, and people with compromised immune systems. Tamiflu® does not immediately cure the flu, but it greatly reduces its duration and helps prevent complications.

Despite the image of mild illness, influenza is responsible for thousands of deaths every year in all countries. People in the risk group described above are the most likely to have complications. Indeed, it is a disease with a very low mortality rate, around 0.3%, but because it is highly contagious (it infects more than 1 billion people every year) it causes many deaths, even if numbers are low.

It is important to remember that the vast majority of people will have multiple episodes of influenza throughout their lives without ever developing complications. Antiviral treatment should only be done after medical evaluation, since 99% of the flu is not indicated to be treated with Tamiflu®.



The signs of seriousness of the flu are:

– Difficulty breathing.
– Chest pain to breathe.
– Low pressure.
– Changes in consciousness.
– Disorientation.
– Persistent vomiting.

pneumonia and tuberculosis chest x rays

Difference between pneumonia and tuberculosis