Infectious diseases are illnesses caused by microorganisms such as bacteria, viruses, fungi, and parasites. While many of these microbes live harmlessly in our bodies, certain conditions can cause them to trigger sickness. Some infectious diseases can also spread from one person to another, making awareness and timely prevention important. They can range from mild infections to life-threatening conditions, depending on the organism involved. Early detection, proper hygiene, and vaccination play a crucial role in reducing their impact.