The flu is contagious starting about one day before symptoms appear and can remain contagious for up to five to seven days after becoming sick

. People are most contagious during the first three to four days after symptoms begin

. Children and individuals with weakened immune systems may remain contagious for longer periods, sometimes several weeks

. To reduce spreading the flu, it is advised to stay home until at least 24 hours after your fever has gone without the use of fever-reducing medications

. The flu virus spreads mainly through respiratory droplets when an infected person coughs, sneezes, or talks, and less commonly by touching contaminated surfaces and then touching the face

. In summary:

• Contagious period: from 1 day before symptoms to 5–7 days after symptoms start
• Peak contagiousness: first 3–4 days of illness
• Longer contagiousness: young children, immunocompromised people
• Isolation recommendation: stay home until fever-free for 24 hours without medication

This timeline explains why the flu spreads quickly and why preventive measures like vaccination, good hygiene, and staying home when sick are important to limit transmission