How do you tell a cold from the flu?

Both are respiratory viral infections but they are caused by different viruses and typically present differently. Colds are most often rhinoviruses and develop gradually over a day or two, with sore throat, runny or stuffy nose, and cough dominating, fever uncommon in adults, and body aches mild. Influenza tends to begin abruptly, with fever, chills, pronounced muscle aches, headache, and fatigue that is disproportionate to the respiratory symptoms, and people frequently describe being able to name the hour it began. Both can produce cough and sore throat, so overlap exists and testing is the only definitive answer.

The distinction matters mostly because of consequences and treatment. Colds resolve on their own and are managed symptomatically. Influenza causes substantial hospitalization and death each year, particularly among older adults, young children, pregnant people, and those with chronic conditions, and antiviral medications including oseltamivir can shorten illness and reduce complications but work best when started within about 48 hours of symptom onset, which is why early testing matters for high-risk people. Annual influenza vaccination reduces both illness and severity and is recommended for nearly everyone over six months.

Two practical points. Neither is treated with antibiotics, which act on bacteria and do nothing for viruses, and unnecessary antibiotic use drives resistance while exposing you to side effects. And warning signs warranting prompt care in either illness include difficulty breathing, chest pain or pressure, persistent dizziness, confusion, inability to keep fluids down, severe weakness, and symptoms that improve and then return with worsening fever, which can indicate a secondary bacterial infection such as pneumonia. In children, add fast or labored breathing, bluish lips, dehydration, and unusual lethargy.