Some 4,000 years ago, Egyptians used lead and lead salts to produce their own make-up to darken and adorn eyes.
Philippe Walter, co-head of a team of scientists from France's Louvre museum and the CNRS national research institute, said the concoctions took up to a month to create.
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"We knew ancient Greeks and Romans too had noted the make-up had medicinal properties, but wanted to determine exactly how," he said.
Contrary to the widely held belief that lead is harmful, the team, using analytical chemistry, determined that "in very low doses lead does not kill cells".
Instead, it produces a molecule - nitric oxide - that activates the immune defence system which beats back bacteria in case of eye infection.
The research was carried out using a tiny electrode, a tenth of the size of a hair, to look at the effect of a lead chloride synthesised by the Egyptians - laurionite - on a single cell.
The study was released online in the journal Analytical Chemistry.
