Colds are caused by flu symptoms. Flu or influenza is caused by a virus that attacks the respiratory system.The virus enters the body of living things and then use it as a place to breed. The virus is transmitted to others through a granular fluid of saliva or mucus are expelled when someone coughs, sneezes, or speaks. The virus quickly spread along with fluids are expelled. Air as a medium for the spread of the virus and if you breathe air with the condition of the body that do not fit can make you the flu. That is why the spread of flu is very easy. Comment not allowed in this page.