11. Headache
Another common symptom of the flu is headache, which can be caused by a number of factors that arise along the duration of the illness. The body’s inflammatory response to an invading pathogen such as a virus triggers the release of substances known as cytokines, infection-fighting chemicals that help the body get rid of sickness. These cytokines have been known to cause some amount of swelling, which explains the headache felt during the flu.
Another reason for flu headaches is pressure which builds up within the sinus cavities of the head. This increase in pressure is brought about by the swelling and inflammation of the nasal passages and the increased production of mucus brought about by the viral infection.
