Final answer:
The most effective habit to prevent the spread of communicable diseases is regularly washing hands with soap and water for at least 20 seconds, which removes pathogens that can cause illness.
Step-by-step explanation:
The most effective habit for preventing the spread of communicable diseases is washing hands regularly. This practice is crucial because microbes, or pathogens, are prevalent on various surfaces like door handles, desks, and even on our own hands. By washing our hands with soap and warm running water for at least 20 seconds, we remove many of the germs that can cause illnesses like the flu, the common cold, and COVID-19. It is important to wash hands often, especially after coughing, sneezing, or touching common surfaces, to prevent microbes from entering our bodies via the mouth, nose, or eyes.