Cleopatra, as famously portrayed by Elizabeth Taylor

The heavy eye make-up favoured by ancient Egyptians such as Cleopatra may have had medical as well as aesthetic benefits, French research suggests.

The study, published in the journal Analytical Chemistry, suggests it helped to protect against eye disease.

The key appears to be lead salts contained in the make-up.

At very low levels, salts produce nitric oxide, which boosts the immune system to fight off bacteria which can cause eye infection.

The make-up used by the ancient Egyptians to darken and enhance the eyes sometimes took up to a month to concoct.

In theory, because it contained lead it might actually have posed a risk to health.

But an analysis by scientists from the Louvre Museum and the CNRS research institute found that in very low doses lead could actually have a positive effect.

Lead researcher Philippe Walter said: "We knew ancients Greeks and Romans too had noted the make-up had medicinal properties, but wanted to determine exactly how."

The researchers used a tiny electrode, 1/10th the thickness of a human hair, to look at the effect of lead chloride salt synthesised by the Egyptians - laurionite - on a single cell.

Writing in the journal, they said: "In stimulating nonspecific immunological defences, one may argue that these lead compounds were deliberately manufactured and used in ancient Egyptian formulations to prevent and treat eye illnesses by promoting the action of immune cells."