In the Middle Ages, the average human life expectancy did not reach into the teen years, not only because of the extremely high perinatal mortality that heavily skewed the data, but also because Europeans (and much of the world during this time) lived in an unhealthy milieu of filth, poor hygiene, and nearly non-existent sanitation. Superstition and ignorance, along with pestilential diseases and vermin infestation, were rampant. Epidemic and endemic diseases such as the bubonic plague, typhus, variola (smallpox), and the White Death of tuberculosis (consumption) took a heavy toll on the population, both young and old.
During the Middle Ages until the mid-nineteenth century cleanliness was just not a priority. The streets in those days were dumping grounds for refuse, and domestic animals including hogs roamed the streets. According to medical historian Howard W. Haggard: "Refuse from the table was thrown on the floor to be eaten by the dog and cat or to rot among the rushes and draw swarms of flies from the stable. The smell of the open cesspool in the rear of the house would have spoiled your appetite, even if the sight of the dining room had not."(2)
There was little improvement in this dire, unhealthy milieu until the mid- to late nineteenth century when the advances of the aforementioned Industrial Revolution and the discovery of the germ theory of disease brought about public health measures that, building upon the importance of good hygiene and sanitation, culminated in the rise of the scientific era of medicine.