Like an Egyptian

Too much lead isn’t good for you and it can cause serious conditions such as brain damage, nevertheless Egyptians used lead salts in their typical black eyeliner. These salts aren’t found in nature and are quite difficult to make, so why did they go trough so much trouble making these components? Ancient manuscripts gave an answer to this question, Egyptians used them as a treatment for eye diseases and scars.
Scientists tested the theory by adding lead salts to skin cells and saw that they started to produce nitric oxide, a compound involved in the body’s immune system, that can kill the bacteria near the eye by breaking down the DNA or other cell structures but it’s not clear yet if it is the nitric oxide that did the job or if it is the lead that directly kills the bacteria.
The fact that it can have a positive effect in small amounts and a negative one in large amounts, fits the hormesis model. Egyptians just didn’t live long enough to experience the harmful consequences of long-term exposure to lead.