Flu: sudden onset, high fever, chills, body aches, exhaustion, dry cough. Cold: gradual build, runny nose, sore throat, sneezing, mild or no fever, and you can still function.
The stakes split them: flu hospitalizes and kills, especially the elderly, infants, pregnant women, and the chronically ill; colds are a nuisance. Action follows the answer: flu plus high-risk or severe means call a doctor within 48 hours of onset, because antivirals work best in that window; otherwise home care, rest, fluids, acetaminophen or ibuprofen, and distance from vulnerable household members during the first 3 days, when contagiousness peaks. Flu's ER flags: trouble breathing, chest pain, confusion, severe vomiting, standing dizziness, or fever that returns with a worsening cough (post-flu pneumonia). The prevention note: the annual flu shot does not stop every case, but it turns truck-hits into grazes, which is the entire case for getting it.
What to do
Common questions
Flu vs cold: how to tell?
The speed and the body slam separate them, per the CDC's flu guidance. Flu: sudden onset (people often name the hour it hit), fever usually 100.4 to 104 F, chills, significant body aches and headache, and exhaustion that puts you in bed for days, plus a dry cough; colds: gradual build, dominated by nose and throat (runny or stuffy nose, sneezing, sore throat), mild or no fever, no real aches, and you can still work through it, annoyed but upright. The stakes differ, which is why the distinction matters: flu lands hundreds of thousands of Americans in the hospital in heavy seasons and kills, especially the elderly, infants, pregnant women, and people with chronic conditions, while colds are a nuisance with no mortality. What to do with the answer: if it is flu and you are in a high-risk group (65-plus, pregnant, chronic conditions, immunocompromised) or symptoms are severe, call a doctor within 48 hours of onset, because antivirals like oseltamivir work best started in that window; for everyone else with flu, the care is home-based: rest, aggressive fluids, acetaminophen or ibuprofen for fever and aches, and isolation from the household's vulnerable members for the contagious window (most contagious the first 3 days). Colds get the same home care minus the urgency. The flu-specific red flags for the ER: trouble breathing, chest pain or pressure, confusion, severe or persistent vomiting, dizziness on standing (dehydration), or fever that improves then returns with a worse cough (a bacterial pneumonia pattern after flu). The prevention note that outranks all of this: the annual flu shot will not stop every case, but it turns truck-hits into grazes, and that is the whole argument for getting it.