Or do health care providers just tell you that so you get tested/
Herpes can take YEARS to show up. for example, up to 80% of the US population tests positive for HSV-1 (oral herpes/cold sores/fever blisters) but never have an outbreak! Recently, a widow of 20 years had her first outbreak of HSV-2, genital herpes, with no sexual contact since her husband died. Often, the infection remains silent and does not present itself unless a person is stressed, ill, undergoes an operation, etc. Many men remain symptomless and continue to spread the disease without knowing it. One of the big issues here is that STD tests do NOT automatically include herpes–you must specifically request they perform that test. if you are infected, it can take up to 4 months to show up in your blood.
Syphilis is another STD that can remain silent for many years–even though it can be detected in STD tests and successfully treated. there has been a recent increase in syphilis because people are not being tested as they should, and it can be fatal if it goes untreated.
HIV/AIDS also can go undetected for years–which is why sexually active people should be routinely tested for STDs. even with testing, HIV often is not detected in the blood for up to six months after exposure.
Many STDs (gonorrhea, chlamydia) cause Pelvic Inflammatory Disease in women, which can result in sterility. That is why it is very, very important if you are sexually active to have routine STD tests.
If you are NOT sexually active, then you are fairly safe not to have the tests, though many doctors will perform them during routine annual exams. BUT if you are sexually active, you should take a new test each time you take on another sexual partner–and demand to see their test as well. never, ever, ever take their word that they are STD-free. they may have been–a year ago. may not be true now!
Yes some stds can take a while to show up because your body can naturally suppress symptoms. they can lie dormant for months or years before showing symtpoms and even then some times the symptoms can be vague. It's not some thing to scare you into getting tested. but you should get tested regularly if you are sexually active because you never know who could have an std out there.