The symptoms of the flu are more severe than the symptoms of a cold, according to WebMD. They also last longer and can lead to serious and even life-threatening complications in some people. Pneumonia is one complication of the flu.
The first sign of a cold is often a sore throat that lasts for up to 48 hours, according to WebMD. Following it are a runny nose, cough and congestion. Fever is not usual in adults but more common in children. At first, the nasal secretions are thin and watery but become darker and thicker over the days. The symptoms usually last about a week, and the person is contagious for the first three days. If the cold lasts longer than a week, the person might have an allergy, sinusitis or a bacterial infection.
Flu also presents with a sore throat, notes WebMD, but other symptoms include fever, head and muscle aches, congestion and cough. Vomiting and diarrhea are also associated with some strains of flu. These symptoms usually improve after a few days, but the person may feel a general malaise for some time. Flu can be dangerous for people who have weakened immune systems or people who are very young or elderly. It also poses a risk for people with pulmonary or heart problems.