Kohl was used in Egypt since pre dynastic times to protect the eyes from disease (presumably trachoma, which is spread by flies. Ever see those photos of starving babies whose eyes are covered with flies? Maybe the poisonous kohl did discourage this from happening).
this has been known since antiquity, but science has confirmed this only recently:
From the NIH:
In trachoma endemic areas, flies are frequently seen clustering around the face and eyes of children where they feed on mucus and discharge (Fig.(Fig.1).1). This association of flies with the faces of infected children has not gone unnoticed, and they have been considered as vectors of trachoma for at least 400 years.1
Everted upper eyelid of a Gambian child with follicular trachoma and a feeding female bazaar fly (Musca sorbens)Flies act as mechanical vectors of disease by picking up pathogens from infectious material and transferring them to an uninfected host. Flies have taste receptors on their front feet and when feeding they dip these into the food source as well as their proboscis. Thus, flies may be transferring Chlamydia trachomatis from the eyes of infected children to the eyes of uninfected people, on their feet and proboscis. However, the transmission of trachoma is poorly understood and there are other suggested routes which may be important in different places and at different times. Trying to prove that a particular route is operating, and establishing the relative importance of one route over another, is difficult. Until a recent intervention trial in The Gambia2 there has been little strong evidence to prove that flies actually are important in the transmission of trachoma.
Factoid: Kohl in India is made from a lead compound, but kohl in Egypt is Stibnite, an antimony based compound.
The NIH points out that lead based kohl puts the user at danger of lead poisoning.
This article from a tourism website notes that both antimony and lead based kohl were used in ancient Egypt.
In ancient Egypt, preparations were a little more extensive. The cosmetic material had to be powdered on a palette and then this powder mixed with a substance, (analysis indicates that these were usually ointments derived from animal fat) to make the powder adhere to the eye.
Eye makeup equipment (palettes, grinders, applicators) has been found among the earliest burials of the pre-dynastic period and seem to have been essential items for the afterlife.
Even the humblest graves consistently contain at least a simple palette. Small containers of galena have been found in tombs alternately stored in leather or canvas pouches, small jars, conch shells or within hollow reeds. What separated rich from poor was not the existence of makeup but the expense and luxury of containers and applicators. Everyone had galena powder however while the poor resorted to sticks to apply it, the wealthy had intricately carved and bejeweled containers of ivory or other precious materials.
That the Egyptians decorated their eyes with great aesthetic care is immediately obvious. Eye cosmetics bestowed beauty and style as well as other gifts, perhaps less immediately apparent to modern eyes.
Galena possesses disinfectant and fly-deterrent properties. It is believed to offer the eyes protection from intense sun. The medical papyri frequently prescribe mesdemet for assorted complaints of the eye.
Eye make up provided psychic protection as well. The Egyptian word for eye-palette seems to derive from their word for "protect." An unadorned and thus unprotected eye was believed vulnerable to the Evil Eye. Outlining the eyes thus became a personal protective amulet drawn right upon the skin; an amulet that once applied could not be lost or misplaced.
Arsenic pesticides didn’t arrive in the United States until the 1860s, when they were used to fight the Colorado potato beetle. Lead arsenate wasn’t introduced until the 1890s when it was used against the gypsy moth. ... In 1919, the Boston Health Department destroyed arsenic contaminated apples because people were getting sick. The follow year, it had to do it again.
and this is worrisome:
Rice is an exception to that. Scientists have discovered that the rice plant, because it’s designed to pull silicon out of the soil (it strengthens the grain) does the same with the structurally similar arsenic. Researchers at Dartmouth College’s Toxic Metals Superfund Research program note that rice has been described as a natural arsenic accumulator. Most of this accumulation, of course, is due to naturally occurring arsenic in soil and water.this book discusses the ancient use of Kohl in Egypt as a fly repellant. LINK Alas, unlike many of the books published by the Metropolitan museum, it isn't a free download.