What causes Flu like symptoms in healthy individuals?

Flu-like symptoms in healthy individuals can be caused by various factors, including viral infections (like the influenza virus or common cold viruses), bacterial infections, or even non-infectious causes such as Allergies or stress. These symptoms often include fever, fatigue, body aches, and cough, which result from the body's immune response to pathogens or irritants. Environmental factors, such as exposure to cold weather or pollutants, can also contribute. In some cases, these symptoms may appear in response to other illnesses or conditions not directly related to the flu.