If you feel fine in the morning but are suddenly hit by a fever of around 38 degrees, chills, and body aches starting in the afternoon, it is easy to confuse whether it is a cold or the flu. While colds and the flu cause similar symptoms like coughing and a runny nose, there are distinct differences in the causative viruses and the way symptoms begin.
The key is not to make a judgment based solely on a runny nose or fever. In this article, I will compare the causes, onset sequence, and patterns of cough, phlegm, and muscle pain associated with the common cold and the flu, as well as summarize the points to look for when distinguishing them from COVID-19 and the signs that require medical attention.
Why Colds and Flu Are Different from the Start
The common cold can be caused by over 200 types of respiratory viruses. Influenza, on the other hand, is a distinct infectious disease caused by the influenza virus, with types A and B being the representative types.
Colds often start gradually in the nose and throat, whereas the flu is characterized by the sudden onset of systemic symptoms. In a cold, sneezing, runny nose, nasal congestion, and sore throat occur first, often leading to coughing or phlegm.
A runny nose and a cough are not symptoms exclusive to a cold, and whether a sudden high fever, chills, and muscle pain occur together is an important clue to suspecting the flu.
Comparison of symptom onset order and intensity
Cold symptoms can be most pronounced around 2 to 3 days after infection. It is common to start with a sore throat or a stuffy nose, followed by a runny nose, sneezing, and coughing as time goes by.
If you experience postnasal drip, where mucus flows down the back of the throat, you may find yourself clearing your throat frequently, and your coughing may worsen at night. The formation of phlegm is also a result of increased secretions from the airway mucosa or continued postnasal drip.
Influenza often begins suddenly with a rising fever and chills. Severe fatigue, headaches, and generalized muscle pain may appear before or simultaneously with a runny nose, making it difficult to carry out daily activities.
| division | cold | flu | covid-19 |
|---|---|---|---|
| cause | various respiratory viruses | Influenza virus | covid |
| Starting pattern | Nose and throat symptoms progress gradually | Sudden systemic symptoms | Various symptoms such as sore throat, fatigue, and cough |
| Common symptoms | Runny nose, sneezing, nasal congestion, cough | High fever, chills, muscle pain, severe fatigue | Sore throat, mild fever, cough, fatigue |
| High fever and body aches | It is relatively rare in adults. | May appear strongly | There is a big difference from person to person. |
Why it is difficult to distinguish based on fever, cough, and runny nose alone
You cannot conclude that you have the flu simply because you have a fever. Children, in particular, tend to develop fevers even from a common cold more often than adults, so distinguishing between a cold and the flu based solely on body temperature can lead to an incorrect diagnosis.
Conversely, the flu does not always manifest only as a high fever and muscle aches. A runny nose and cough can occur with the flu, and COVID-19 can also start with symptoms like a sore throat or a runny nose, similar to a common cold.
COVID-19 manifests primarily as a sore throat, mild fever, cough, and fatigue, and lethargy or muscle pain may be more pronounced than with a common cold. It is worth noting that while a cold often begins with a runny nose and sneezing, a sore throat is sometimes felt first with COVID-19.
It is difficult to completely distinguish between the common cold, the flu, and COVID-19 based on symptoms alone. Influenza tests are conducted at medical institutions, and it is suggested to retest after 24 hours if symptoms persist even if the COVID-19 self-test comes back negative.
Do not delay medical treatment in such cases.
If you experience shortness of breath, difficulty breathing, or chest pain, you should not dismiss these as simple cold symptoms. You also need to seek medical attention if you have a persistent fever of 38 degrees or higher, find it difficult to drink water, or experience impaired consciousness.
If a child becomes lethargic, sluggish, or complains of severe generalized pain, their condition must be carefully monitored. Early intervention is also crucial for the elderly and those with underlying conditions such as diabetes and hypertension, as symptoms can worsen rapidly.
Influenza can progress to complications such as pneumonia in some patients. A persistent high fever or a resurgence of cough and breathing symptoms that had been improving are signs that you should seek medical attention sooner.
Things to take care of in daily life while sick
If you have a fever and a cough, it is safer to reduce outings and gatherings, and to avoid sharing towels, dishes, and other items with others. Washing your hands with soap and running water for at least 30 seconds helps prevent respiratory infections.
Replenish fluids in small amounts frequently rather than drinking a large amount at once. Getting enough rest while monitoring your body temperature, breathing status, and water intake helps you avoid missing the progression of worsening symptoms.
Cold medicine is used to reduce symptoms such as a runny nose or cough, but it does not directly treat the influenza virus. If you experience a sudden high fever and muscle pain severe enough to suspect the flu, it is necessary to identify the cause through medical examination and testing rather than trying to endure it on your own.
A runny nose, sneezing, and sore throat that start gradually resemble a common cold, while a sudden high fever, chills, muscle pain, and severe fatigue are more common symptoms of the flu. However, since the symptoms overlap, do not rely solely on body temperature; first check for shortness of breath or severe lethargy.