lack of any plumbing. (people used chamber pots instead of toilets.)
Disease from lack of plumbing and hygiene. (people didn't know they needed to wash their hands)
Dense population not much personal space. Contagious disease spreads easily.
In the early 1900's there were factories in cities that caused lots pollution. Air pollution and water pollution. Both types led to shorter life expectancy and health problems.
The city residents who worked in the factories faced possible death from the dangerous machine conditions. People lost body parts and could burn themselves
