Flu is a common cold like condition but only severe and is generally caused by virus. Symptoms Symptoms of flu are like those observed during common cold but more severe.These include fever,body aches,cough which are the more common symptoms.In some situations,headaches and nausea is also observed. Root causes Flu is caused by a virus that spreads through coughs and sneezes. It could also be caused due to living an unhygienic environment and faulty eating habits.