What are the symptoms of the flu?

Generally speaking, flu refers to influenza. Symptoms of influenza include fatigue, headache, nasal congestion and runny nose, cough, high fever, etc. The specific analysis is as follows:

1. Fatigue

Influenza virus infection causes the body's immune system to consume a large amount of energy to fight against the virus. Meanwhile, viral replication and inflammatory responses can also lead to a decline in physical function, making patients feel fatigued.

2. Headache

Influenza virus infection can cause increased intracranial pressure or inflammatory responses, resulting in headaches. Additionally, high fever and muscle pain may also indirectly cause headaches, typically presenting as pain near the temples or throughout the head.

3. Nasal Congestion and Runny Nose

When the influenza virus attacks the upper respiratory tract, it causes an inflammatory response in the nasal mucosa, leading to mucosal congestion, edema, and increased secretions. These changes can cause symptoms such as nasal congestion and runny nose.

4. Cough

The influenza virus mainly affects the upper respiratory tract, including the nasal cavity, pharynx, and larynx. When the virus replicates in these areas, it causes mucosal inflammation and edema, stimulating the cough reflex and resulting in coughing.

5. High Fever

When the influenza virus replicates in the body, it triggers an immune response that causes the body's temperature set point to rise, leading to a rapid increase in body temperature, which may exceed 39°C and last for several days.

However, it should be noted that the severity and duration of influenza symptoms may vary among individuals. Elderly people, pregnant women, infants, young children, and individuals with chronic diseases should seek medical attention promptly when experiencing symptoms of influenza.