Contagious diseases are illnesses that can spread from one person to another, often through direct contact or airborne transmission. Common examples include influenza, measles, and COVID-19. These diseases are caused by pathogens like bacteria and viruses, which can be transmitted through sneezing, coughing, or touching contaminated surfaces. Preventing the spread of contagious diseases involves practicing good hygiene, such as regular handwashing and using hand sanitizers. Vaccinations are also crucial, as they help protect individuals and communities from outbreaks. Public health measures, like wearing masks during epidemics, can further reduce transmission rates and keep populations safe.