The symptoms? A blocked nose, sore throat, constant coughing and the shivers. Surely it can mean only one thing - you've got the flu.

Not necessarily, say the doctors. In fact the chances are you've come down with something far less menacing - a common cold.

All too often the two very similar, yet very separate, illnesses are confused as the same. Specifically, cold victims tend to overstate their ailment by claiming they've been struck down by the flu.

To an extent, they can be forgiven, says Professor Ron Eccles of Cardiff's Common Cold Centre.

The elderly are most at risk from flu

"I'm not surprised people tend to get them mixed up. It's impossible for the average person to separate a severe cold from a mild flu," he says. "They are both generally referred to as 'flu-like illnesses'."

But he agrees victims often plump for the more drastic option because it "tends to sound more serious" and generate "more sympathy".

"Undoubtedly people tend to tell the boss they've got flu when they only have a cold. It sounds better if they want time off work.

"But not everything that causes red spots on the skin is chicken pox."

Key symptoms

Both are caused by viruses, says Prof Eccles, but these are as "different as a cat from a dog".

Common cold symptoms are:

• A scratchy, sore throat
• A blocked or runny nose
• A cough

Whereas common flu symptoms include:

• Spells of high fever (hovering above 101°F) and chilliness
• Severe muscle aches and pains
• Followed later by the traditional cold symptoms
  (Flu also tends to have a more sudden on-set)

Both tend to last for about five or six days in a normally healthy person, and are transmitted in similar ways - cough, sneezing and fingers made dirty from being poked in the nose and eyes.

Killer virus

The effects of flu can also be far more serious. It can cause pneumonia and kill its victims.

"Historically, influenza has killed far more people than any other viral disease, including the likes of the black death," said Prof Eccles.

And it's not just the elderly and young babies who are at risk, he says, pointing out that many of the 20 million killed in the 1919 flu epidemic were young men and women.

Vaccine available

More severe it may be but the flu does have one advantage. There is a vaccine against flu but not for the common cold.

Colds are caused by the huge family of viruses called rhinoviruses. With more than 80 different constantly mutating rhinoviruses, vaccination is impossible.