Colds tend to develop slowly over a day or two and mainly cause a runny or blocked nose, sneezing, and a sore throat. You can usually carry on with most daily activities. Fever is uncommon or mild in adults with a cold.
Influenza typically hits hard and fast. Within hours you can have a high fever, marked muscle and joint aches, headache, dry cough, and overwhelming tiredness that often forces you to rest in bed. These whole-body symptoms are the main clue that points to flu rather than a cold.
The distinction is not always clear-cut, and only a test can confirm influenza. What matters more is how unwell you are. Seek urgent care for difficulty breathing, chest pain, confusion, bluish lips, or symptoms that rapidly worsen, regardless of the label.