There is much more to eyeliner than meets the eye. Ancient Egyptians believed that eye makeup was not only worn and ‘blessed’ by gods, but also had the power to fight off evil and ward off infections — and it appears they may have been right about the makeup’s capacity to be protective.

Green and black makeup was used extensively in ancient Egypt on various occasions for aesthetic and therapeutic purposes. After extensive study, chemists have concluded that the alluring and mesmerizing eye makeup used by ancient Egyptians — including queens like Nefertiti — was not only for beauty but also for protection against infections and ophthalmic diseases.

In a 2010 study published in the journal Analytical Chemistry, researchers analyzed samples of ancient Egyptian makeup found in the Louvre museum. Using electron microscopy — used to view magnified images of specimens — and X-ray diffraction — used to determine a material’s structure by the scattering angles and intensities of reflected rays — the authors found that many of these makeup items, especially items designed for the eyes, had significant amounts of lead-based chemicals in varying compounds.

Researchers identified four recurring lead compounds, two of which can only be made synthetically. When tested on human cells, these two compounds yielded surprising results: the makeup boosted the production of nitric oxide in the cultured cells by over 2.4 times the original production. In other words, the cells treated with the two lead compounds began pumping out more nitric oxide than cells not treated with lead!

These lead compounds contain lead ions, which induce lab-grown human skin cells to overproduce nitric oxide. Nitric oxide is an essential component in our bodies because of its role as a messenger in the immune system, relevant for signalling to various physiological systems. Thus, the boost in its production following the application of lead compounds found in ancient Egyptian eye makeup might have been essential for different systems within the body like the nervous system, the immune system, and the cardiovascular system. According to Christian Amatore, a chemist and one of the study’s investigators, nitric oxide is also responsible for setting off a biochemical chain reaction that eventually recruits immune cells which engulf and destroy foreign microorganisms at the site of infection.

On the other hand, Martin Olivier, an immunologist at McGill University, proposes either that nitric oxide itself directly severs bacterial protein or bacterial DNA — or both — or that lead stimulates immune cells already in the eyelid. Though modern scientists have dismissed lead’s potential for protection, since the substance is more famously known for its toxicity, lead does offer some health benefits when applied to the skin. As such, in this case, lead can serve as an example of  “hormesis,” which is a term for cases where low doses of exposure to a substance could be beneficial while consistent levels of exposure could be harmful.

Whether it is nitric oxide or lead that stimulates immune cells to attack bacteria, or nitric oxide itself that deals with bacterial components, it is fair to presume that the eyes of ancient Egyptians adorned with this black liner would have had good protection from bacterial contamination!

Chemists under Nefertiti’s reign may have figured out that makeup with lead compounds, like laurionite, had more health benefits than makeup without it. Still, it must be noted that long-term exposure to a substance like lead is bound to have severe detrimental effects on cells and the human body, with the dangers of lead poisoning outweighing their antibacterial properties.

Our present-day eyeliners contain not only lead but also other metallic compounds like arsenic, mercury, and aluminum, and while they may not have severe detrimental impacts in the short term, significantly prolonged uses can be dangerous. Thus, it is important to understand the long-term impacts of such products and to take necessary precautions. As such, you shouldn’t sleep with your eyeliner on or continue to use that eyeliner at the bottom of your makeup bag for years.

Still, the next time you are rushing to class, don’t underestimate the importance of a bit of eyeliner: not only is it Nefertiti-esque, it is also an immunostimulant!