Ancient Egyptians are known for their elaborate dark-rimmed eyes, courtesy of lead and arsenic-based makeup. Today, experts are well-aware of the dangers of such poisons in makeup. But a recent study published in Analytical Chemistry, the semimonthly journal of the American Chemical Society, shows the lead-based makeup used by the Egyptians had antibacterial properties that helped prevent common infections at the time.

Christian Amatore is a chemist at the École Normale Supérieure in Paris and one of the paper’s authors. As lead and arsenic famously causes brain damage, Amatore tells The  New York Times, “It was puzzling; they were able to build a strong, rich society, so they were not completely crazy.” But as it turns out, it is the dose that makes the poison. A low dose would have killed bacteria. A high dose would have killed the wearer.

The Times reports that the study, conducted by Dr. Amatore and his fellow researchers, used X-ray diffraction and electron microscopy to analyze 52 samples from containers of Egyptian makeup preserved at the Louvre. They discovered that the makeup was primarily based on four different lead chemicals which, when mixed, provided gloriously rich colors. However, because of disintegration over the centuries, scientists were unable to determine the percentage of lead in the makeup.

Evidence exists that the Egyptians thought their makeup was magical. Dr. Amatore points out that the Egyptians sang incantations while they were mixing the makeup. Since eye infections caused by particles were common in Ancient Egypt, this “magical” lead makeup may have acted as a toxin, killing bacteria before it spread.

While small doses of lead continue to be found in modern makeup, (much to the bane of clean beauty advocates,) don’t start adding it to your eyeliner. According to Neal Langerman, a physical chemist and health safety advocate, “You probably won’t want to do this at home, especially if you have a small child or a dog that likes to lick you.”

For further reading: Ancient Egyptian makeup fought bacteria, researchers say.

Toxic lead makeup in ancient Egypt may have fought infections
New research shows early Egyptian makeup had antibacterial properties.