Although syphilis chancres are reasonably easy to spot on the external genitalia, as you can see in these syphilis pictures, there is a growing epidemic of syphilis being spread by oral sex. Because the sores are painless, chancres may go unnoticed or misdiagnosed if they occur in the mouth. As such, orally transmitted syphilis infections are more likely to go undetected and untreated.
A chancre will usually heal on its own in three to six weeks, but that does not mean the underlying syphilis infection is gone. If left untreated, syphilis can lead to systemic health problems and even death. That is why testing is essential if you believe you may have been exposed to syphilis.
It is particularly important for pregnant women to be screened for syphilis because of the possibility of congenital syphilis spreading to the newborn.