I assume this statement applies primarily to Europeans. I recall the pre-modern natives of America thought the Europeans unhygienic. The natives bathed frequently, sometimes several times a day. The "dirty" Europeans ignored methods of personal care used by the natives. The Indian people were remarkably free of disease with the predominant disorders being external injuries, arthritis, digestive disorders and respiratory infections. Cancer, heart disease and nuerological problems were rare.
-Simply because life expectancy in those societies was something in the -range of 30-35 years, to few time to develop cancer and atherosclerosis. -Also remember that cancer diagnosis requires pathology facilities that -were completely unknown up to 1800´s, so pre industrial "low cancer rates" -maybe simply due to underdiagnosis....
Alexandre Fenelon