Syphilis - Causes of syphilis
NHS Choices Medical Reference
Syphilis is caused by bacteria called Treponema pallidum. The bacteria can enter your body if you have close contact with an infected sore, normally during vaginal, anal or oral sex or by sharing sex toys.
It may also be possible to catch syphilis if you are an injecting drug user and you share a needle with somebody who is infected.
Pregnant women can pass the condition on to their unborn babies, which can cause stillbirth or death of the baby shortly after labour.
It is extremely rare for syphilis to be spread through blood transfusions as all blood transfusions in the UK are routinely tested for syphilis.