A sexually transmitted infection (STI) is an infection that is primarily spread through sexual contact. This includes vaginal, anal, and oral sex. Common STIs include chlamydia, gonorrhea, syphilis, and human immunodeficiency virus (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 certain infections, like human papillomavirus (HPV) and hepatitis B. Early detection and treatment are crucial to managing STIs and reducing their spread.