Why your body struggles to distinguish a cold from the flu

Science · Published 25 October 2026 Swipe more like this →

In short: Both illnesses are contagious respiratory infections that can leave you feeling miserable, but they aren't the same beast. While they share many overlapping symptoms, understanding the underlying viral mechanics and intensity of the onset is key to knowing when a simple rest is enough or if medical intervention is required.

While both common colds and influenza (the flu) are contagious respiratory illnesses, they originate from entirely different viral families. The flu is caused exclusively by influenza viruses. In contrast, the common cold is more diverse, triggered by a variety of different viruses including rhinoviruses, parainfluenza, and seasonal coronaviruses. It is important to note that these seasonal coronaviruses are distinct from SARS-CoV-2, the virus responsible for COVID-19. These pathogens are all highly contagious and spread between people. The diversity of cold-causing viruses makes it a complex respiratory landscape.

Because they share many symptoms—such as cough, sore throat, runny or stuffy nose, headaches, fatigue, and muscle aches—it can be difficult or even impossible to tell them apart based on physical sensations alone. However, there are general patterns of intensity. Flu symptoms typically begin more abruptly and are generally more intense than those of a cold. While people with colds are more likely to experience a runny or stuffy nose, the flu is often characterized by more significant systemic effects like fever or chills. Patients with the flu may feel feverish or experience significant body aches alongside their primary symptoms. These sensations often occur simultaneously during the initial onset.

The most critical distinction lies in the potential for severe complications. Serious medical issues like hospitalisations, pneumonia, or bacterial infections are rarely caused by common colds. The flu, however, can lead to serious associated complications. Because of these differences in severity and risk, special tests are available to confirm if a person is specifically sick with the flu, allowing for more targeted management during peak illness seasons. Healthcare providers use specific diagnostic tests to differentiate these illnesses accurately. This information was last reviewed by subject matter experts on August 8, 2024.

General information, not professional advice. Spotted an error? Flag the card or see corrections and complaints.

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