Communicable diseases are illnesses that can be transmitted from one person to another, often caused by pathogens like bacteria, viruses, or parasites. These diseases can spread through various means, including direct contact, airborne transmission, or contaminated surfaces. Common examples include influenza, tuberculosis, and COVID-19. Preventing communicable diseases involves practicing good hygiene, such as regular handwashing and vaccination. Public health measures, like quarantines and health education, also play a crucial role in controlling outbreaks. Understanding how these diseases spread helps individuals and communities protect themselves and reduce transmission risks.