Gloios was the matter scraped off the skin with a
strigil after a person was massaged with olive oil at the ancient Greek or Roman
bath house. A
slave would wipe the gloios off into a container with his hands, and it would be collected by a concessioner who would heat and filter it and sell the thick, purified liquid for medical use. In addition to olive oil, it must have contained sweat and
sebum, as well as dirt, hair, and dead skin.
In its purified form gloios was prescribed for toothache and for dyeing the hair blond in ancient times (for the latter you are supposed to add the lees of wine and let it stay on your hair all night). The efficacy of these treatments has not been confirmed in modern times, but many of the "home remedies" described by Pliny the Elder seem totally outlandish. Gloios, however, was the basis of a substantial business in the classical world, and may have had legitimate uses. It is not the only ancient medicament made of what we would probably consider dirt, such as verdigris from copper statues and spearheads, and suint from wool. Guano (bird dung) was put in unguents used on the hair, and that makes some sense since it is rich in urea, an exfoliant still found in some anti-dandruff shampoos. There is another sustance called patos about which I have been able to learn little - it seems to be another name for scrapings from the body.
The word gloios is apparently related to the English word glue.
I would be grateful to receive corrections from people more knowledgeable than myself.