Millions of people throughout the world suffer from them every year. Children and the elderly are the groups most likely to contract them. The two diseases are very similar; both are viral infections of the respiratory tract, and both share common symptoms. Therefore, it can be difficult to tell the difference between them.

The main difference between influenza, or flu, and a cold is that flu symptoms are more severe. Symptoms may appear suddenly, at an already rather severe stage (high fever, extreme fatigue, etc.). Cold symptoms are less severe and come on gradually.

Influenza may lead to more serious illnesses such as bronchitis or pneumonia. This usually happens in people at higher risk, such as the elderly or those with existing chronic conditions. With a cold,  there are generally no serious complications; the most frequent is the development of sinusitis.

Both colds and influenza are recurrent diseases, and they can reappear more than once in the same year. Adults may have from one to three bouts of flu a year, and the same amount for colds. Children can contract even more, from six to ten a year.