The common cold and flu (influenza) are very common infections of the upper respiratory tract (nose, throat, ears and sinuses). Symptoms include a sore throat, a runny or blocked nose, headache, chesty cough, fever, body aches and pains. Colds are one of the most common illnesses in the world.

Colds and flu are caused by viruses. The infections are contagious, passed on by tiny droplets and hand contact. There are hundreds of different types of virus that can cause a cold, which explains why children get repeated colds. Flu is caused by the influenza virus. There are three major types: A (often the cause of flu epidemics), B and C. The flu virus is constantly changing its structure, so new strains appear each year. We don't have immunity to the new strains, which is why we can catch flu repeatedly.

Your bodies first line of defense is the mucus in the nose and throat. This helps to trap the 'invaders' before they have entered the blood system, allowing you to get rid of them by coughing or sneezing.

Anyone can catch a cold or flu. The peak season for colds is the colder winter months, not only because of the weather but because central heating dries out the normally moist nasal mucosa - an important defense against invading viruses. Some children are at particularly high risk from the complications of flu, for example those who are immunosupressed or have chronic lung or heart disease.