Natural infections occur when harmful microorganisms, such as bacteria or viruses, invade the body and multiply. This can happen through various routes, including inhalation, ingestion, or direct contact with contaminated surfaces. The body's immune system responds to these infections by activating defenses to fight off the invaders. These infections can lead to various illnesses, ranging from mild conditions like the common cold to more severe diseases such as influenza or COVID-19. Natural infections can also provide immunity, as the body learns to recognize and combat the specific pathogens, which can help protect against future infections.