Soap , Deforestation and Plagues .
The use of solid bar soap played a significant role in the fall of the Western Roman Empire .
Up to about 100 AD , every person in the Empire was inspected once a day in the baths by their peers . Anybody with anything funny about them was subjected to increasing peer pressure . Contagious systems were picked up quickly .
Personal cleansing was by olive oil and strigil .
Then mass soap arrived . The emphasis is on mass .
Soaps until then were mostly soft soaps used for clothing . This was made of lye (from wood-ash) and animal fats . Solid soap ( ie bars of soap) needed the addition of salt . All these components were expensive , and became more so as the deforestation expanded around the Italian peninsula .
Ironically , the Empire made possible the trade in salt , which made possible that every person in the Roman empire could have a alkaline , salty bar of solid soap . This would first be noticed in the Gallic and Germanic provinces , (woods for the lye , cattle for the fat , salt trade for the salt) .
The poorer classes (ie most of the population) used more and more soap instead of expensive olive oil .
(Olive oil was used for cooking , lighting , personal hygene,lubrication , etc . Typical capitalist overstretch)
The bar soap in the baths and the laundries stripped the protective layer of skin-oils .
The alkali (lye) caused deep cracks in the skin of those using it .
Pathogens which had evolved over thousands of years to face a barrier of oil and super-surface-antibodies suddenly had a free hand . Plagues resulted as pathogens used the newly opened pathways.
The irony is that the Christian fundamendalists around 1200 AD who thought that cleanliness was the problem , was correct . Dirty was better than washing in a communal pool with bar-soap .
We still do not have communal hot-baths in the West .
It was the soap that killed them .And the dirty barbarians on the borders survived .