metals are a public health concern, where especially lead may cause negative health impacts to human fetal and infantile development, a study in Pakistan of pregnant women's nails in 2016, showed thirteen nail samples out of 84 nails analyzed, contained lead higher than the concentration (13.6 μg/g) of the fatal lead poisoning case, with the possibility of an external contamination. The observations showed that lead-containing surma consists of fine particle of galena (ore of lead sulfide) in respirable dust range (less than 10 μm) and relative in vitro bioavailability of lead in the surma was determined as 5.2%. Thus, lead-containing surma consists of inhalable and bioavailable particles, and it contributes an increased risk of lead exposure. "Blue" kohl is a dark-bluish black pigment composed of both lead-based compounds as well as a compound of antimony. The lead-based compounds in kohl are galena (PbS) – dark grey and gloss laurionite (PbCl(OH)) – white phosgenite ((PbCl)2CO3); cerussite (PbCO3) – blue. The antimony-based compound in kohl is stibnite (Sb2S3) – blue. In January 2010, French researchers reported that the particular heavy eye makeup that ancient Egyptians wore may have had medical benefits. At submicromolar concentrations, the specially made lead compounds can elicit overproduction of nitric oxide (NO), which in turn can trigger an enhancement of the immune response. The ancient Egyptians, documented in the Ebers Papyrus ( 1550 BCE), discuss these compounds within kohl as protective for the eyes. Indeed, kohl was used an eyeliner and cosmetic. There are a number of endemic ocular diseases in the Nile region including trachoma – which is caused by a chlamydial bacterium and can cause corneal scarring – and conjunctival cicatricial disease, with visual loss. Kohl was used not only as a cosmetic but also as a medicinal collyrium (from Gr. kollurion). Two of kohl's lead compounds – the lead chlorides laurionite and phosgenite – were not natural to the Nile valley. It is believed they were intentionally synthesized by the ancient Egyptians for this purpose. The widespread use of kohl across the Mediterranean and the Middle East attests to its ability to protect the eye from infectious disease and be used as a cosmetic. Legal status In the United States, kohl is not on the list of color additives approved by the Food and Drug Administration, which considers kohl unsafe for use due to its potential lead content. It is illegal to import into, or