Many have no clothes and are forced to wear the same set for months. They sleep on the floor, only the luckiest have a mat to sleep on. Soap is a luxury that they receive only once or twice a year. The amount of food they receive is scarce. If one's family lives far or if it's too poor to bring clothes or food, one runs the risk of severe under-nourishment.
Hygienic conditions are very bad as well.
To Fall sick in jail Life in jail heavily undermines one's health. Under-nourishment is a first and immediate cause of the weakening of one's body and so it also opens the way to many kinds of illnesses. But also the lack of room and of adequate hygienic conditions facilitate the upcoming of severe pathologies, tuberculosis, cholera, which often bring to death. So, for a small crime one risks one's life. Freedom, at the right time, doesn't only mean to improve one's existence, often it means to save it.