An infection occurs when microorganisms—bacteria, viruses, fungi, or parasites—enter the body, multiply, and cause illness. The body's immune system typically fights infections, but when pathogens overcome defenses or the immune system is compromised, illness results. Infections spread through various routes: respiratory droplets (colds, flu, COVID-19), contaminated food or water (foodborne illness), direct contact (skin infections), sexual contact, blood exposure, or insect bites. Symptoms vary by infection type and severity but commonly include fever, fatigue, and localized symptoms at infection sites. Treatment depends on the pathogen: antibiotics treat bacterial infections but don't work against viruses, while antiviral medications help with some viral infections. Prevention strategies include handwashing, vaccination, food safety practices, safe sex, and avoiding exposure to infected individuals. Public health systems monitor infections, investigate outbreaks, and implement control measures. Understanding infection basics helps individuals protect themselves and make informed health decisions.