An STD can show up anywhere from a few days to several weeks after exposure. Some STDs present no symptoms, making them harder to detect, states Mayo Clinic.
The only way to verify the presence of a sexually transmitted disease is through appropriate testing. This can be performed at most doctor offices and clinics. If an STD is detected, a doctor can diagnose it and administer proper treatment. Most STDs clear up with medicine, although there are exceptions. The only guaranteed way to prevent an STD is to abstain from sex completely, according to the Centers for Disease Control and Prevention.