Sexually transmitted infections, or STIs, are sometimes also called sexually transmitted diseases or STDs but they mean the same thing. Did you know that about half of sexually active teens and young adults will get an STI before their 25th birthday – and many of them will have no idea? Abstaining from sex is the only 100% way of protecting yourself from getting an STI – or giving one to someone else. But if you are having any kind of sex, or thinking about getting started, learn about STI prevention and transmission below and use condoms to protect yourself and your partner. Since the most common symptom of STIs is having no symptoms at all, it’s important to get tested and treated as soon as possible. STIs are easy to treat, but if left undetected, they can cause long-term health problems. Teens in CA can get STI prevention and treatment services for FREE.