Sexually transmitted infections (STIs) are infections that are primarily spread through sexual contact. They can be caused by bacteria, viruses, or parasites and may affect anyone who is sexually active. Common STIs include chlamydia, gonorrhea, syphilis, and HIV. Many STIs can be asymptomatic, meaning individuals may not show symptoms but can still transmit the infection to others. Preventing STIs involves practicing safe sex, such as using condoms and getting regular health check-ups. Vaccines are available for some infections, like human papillomavirus (HPV) and hepatitis B. Early detection and treatment are crucial to managing STIs and reducing their spread.