Soap and water and common sense are the best disinfectants.

The line distills a practical, early–public-health ethos: the most effective protections against infection are not exotic remedies but basic hygiene and clear judgment. “Soap and water” points to handwashing and cleanliness as frontline measures, while “common sense” underscores behavioral choices—avoiding needless exposure, maintaining sanitary surroundings, and not being misled by fads or false assurances. Attributed to Osler, the sentiment aligns with the late-19th/early-20th-century medical shift toward germ theory and preventive medicine, emphasizing that everyday practices can outperform complex interventions when consistently applied.